LD400+LD400P Instruction Manual Iss2

User Manual:

Open the PDF directly: View PDF .
Page Count: 54

Download
Open PDF In Browser	View PDF

LD400 & LD400P
400W DC Electronic Loads

INSTRUCTION MANUAL

Table of Contents
Specification

EMC

Safety

Installation

Connections

Initial Operation
Organisation of this manual
Connecting the Load to the Source
Switching On

14
14
16
16

Front Panel Operation
Keys and ∆ Adjust
The Display and the Home Screen
General Numeric Entry of Parameters
Variation of Parameter Values using ∆ Adjust
Configuring the Load
Selection of Load Mode
Level A and Level B Setting and Range Selection
Dropout Voltage
Slow Start
Introduction to Transient Operation
Transient Menu
Voltage and Current Limits
Short Term or Intermittent Operation at up to 600 Watts
Store and Recall Facilities
Utilities Menu

17
17
17
19
19
19
20
20
20
21
21
22
24
24
25
26

Analogue Remote Control

Application Notes
Stability of Source and Load Combinations
Dynamic Behaviour in Transient Operation
Start-up transients
Characteristics of each Operating Mode
Multiple Unit Operation
Zero Volt Operation

28
29
29
30
30
33
33

Remote Interface Configuration
GPIB Interface
RS232 Interface
USB Interface and Device Driver Installation
LAN Interface

34
34
34
35
35

Status Reporting

Remote Commands

Maintenance
Troubleshooting

48
48
1

Full operating and programming instructions for this instrument can be found in the
appropriate product folder of the accompanying CD-ROM.
This information can also be downloaded from the support page of the Aim-TTi website.
This manual is 48511-1730 Issue 2.

Français
Sécurité

Les instructions complètes de fonctionnement et de programmation de cet instrument se
trouvent dans le dossier approprié du CD-ROM
d’accompagnement. Ces informations sont également téléchargeables depuis la page de
support du site Internet de Aim-TTi.
Numéro du manuel 48511-1730, 2 édition.

Deutsch
Sicherheit

Vollständige Betriebs- und Programmieranweisungen für dieses Gerät finden Sie im
entsprechenden Produktordner der beigefügten CD-ROM.
Diese Informationen können auch von der Support-Seite auf der Aim-TTi-Website
heruntergeladen werden.
Dieses Handbuch trägt die Nummer 48511-1730 Ausgabe 2.

Italiano
Sicurezza

Le istruzioni complete per il funzionamento e la programmazione dello strumento sono
incluse nella relativa cartella del prodotto del CD-ROM fornito.
È anche possibile scaricare queste informazioni dalla pagina dell’assistenza del sito Web
Aim-TTi.
Questomanuale è la versione 48511-1730 revisione 2.
.

Español
Seguridad
Las instrucciones completas de funcionamiento y programación de este instrumento
pueden encontrarse en la carpeta del producto correspondiente en el CD-ROM adjunto.
También es posible descargar esta información desde la página de asistencia de la web
de Aim-TTi.
Este manual es el 48511-1730 versión 2.

Introduction
This DC electronic load is intended for use in investigating the behaviour of many different types
of DC power sources such as batteries, solar cells, fuel cells or wind generators, as well as
electronic power supply units.
It is designed to have very low internal resistance to allow operation at high currents with low
voltage drop. The voltage of the source can be sensed either internally for convenience or
externally for better accuracy.
The unit provides five different operating modes: constant current, constant power, constant
resistance, constant conductance and constant voltage.
It operates over the current range 0 to 80 Amps and the voltage range 0 to 80 Volts with a
continuous power dissipation capability of up to 400 Watts. It also permits short term dissipation
up to 600W, for brief or intermittent testing of higher power sources.
A low voltage dropout facility is provided to protect sources such as batteries from damaging
levels of discharge by reducing the load current when the source voltage falls below the dropout
threshold setting.
An internal transient generator can repeatedly switch the load between two different operating
levels, level A and level B. The frequency and duty cycle of the transients can be set over a wide
range. The transients can also be initiated by an external logic signal. The transitions between
the levels have a true linear slewing characteristic in all modes, with the slew-rate being
adjustable over a wide range.
The unit meters and displays measured values of Volts & Amps and equivalent Watts & Ohms. A
monitor output providing a voltage proportional to the current flowing allows the behaviour of a
source to be viewed on an oscilloscope or external meter.
All adjustable system parameters can be set via numeric keyboard entry or via the digital remote
interfaces for quick and convenient instrument control.
Up to 30 non-volatile storage locations can be used to store and recall instrument parameter set
ups, ideal for test and calibration procedures.
An external control voltage can also be used to set the level of the load. Any desired waveform
can be applied, with the internal slew rate control circuit remaining active to provide additional
control.
The unit is fully protected against excessive current, power dissipation or internal temperature,
and minimises audible noise by automatically controlling the fan speed according to the power
dissipation.

Specification
Accuracy specifications apply for 18°C – 28ºC, using the rear panel terminals, at 50W load power
(in normal 400W mode), after 30 minutes operation at the set conditions; regulation specifies
variation at other powers. Setting accuracies apply with slew rate at the ‘Default’ setting.
Superscript references are to footnotes on page 7, which provide further clarification.

INPUT
Maximum Input Ratings
Current:

80 Amps max. through the rear panel terminals.
30 Amps max. through the front panel terminals.

Voltage:

80 Volts max. while conducting current.
Surge suppressors start to conduct at 120V (nominal),
Max. non-repetitive surge energy: 80 Joules.

Power:
(1)

continuous:
short term mode:

Minimum Operating Voltage:
Off State Leakage:
Reverse Polarity:
Isolation Voltage:

400 Watts max. up to 28ºC, derating to 360 watts at 40ºC.
600 Watts max. up to 28ºC, for up to 60 seconds on-time, with
off-time at least double the on-time.
<2V at 80A; typically equivalent to 25mΩ above 100mV (at 4A).
<10 mA (including voltage sense circuit input resistance).
Diode will conduct; 80 Amps max.
± 300Vdc max, either load input to chassis ground.

Input Terminals
Rear Panel Input:

Safety terminals accepting 5mm diameter wire, or 8mm spades, at
80 Amps max. or 4mm plugs at 30 Amps max.

Front Panel Input:

Safety terminals accepting 4mm diameter wire, 4mm plugs or 6·5mm
spades. 30 Amps max.

External Voltage Sense
Connection:
Input Impedance:
Max. Sense Voltage Offset:

Terminal block on rear panel. Sense selection by slide switch.
680kΩ each input to load negative.
6V (allowance for backing-off supply for zero volt operation).

OPERATING MODES
Constant Current Mode (CC)
Current Ranges:

0 to 8 A (1 mA resolution) and 0 to 80 A (10 mA resolution).

Setting Accuracy:

± 0·2% ± 30 mA.

Regulation:

< 30 mA for 90% load power change (V > 2 Volts).

Temperature Coefficient:

< (±0·02% ± 5 mA) per ºC.

(2)

(3)

Slew Rate Ranges:

8 A range:
80 A range:

Minimum transition time:

50 µs.

2·5 Amp per s to 250 Amp per ms.
25 Amp per s to 2500 Amp per ms.

Constant Power Mode (CP)
Power Range:

0 to 400 (or 600) Watts.

Setting Accuracy:

± 0·5% ± 2 W ± 30 mA.

Regulation:

< 2% over 5 V to 75 V source voltage change (using remote sense).

Temperature Coefficient:

< (± 0·1% ± 5 mA) per ºC.

(2)
(3)

Slew Rate Ranges:

40 W per s to 6000 W per ms.

Minimum transition time:

150 µs.

Constant Resistance Mode (CR)
Resistance Ranges:

0·04 to 10 Ω (0·01 Ω resolution) and 2 to 400 Ω (0·1 Ω resolution).

Setting Accuracy:

±0·5% ± 2 digits ± 30 mA.

Regulation:

< 2% for 90% load power change (V > 2 Volts, using remote sense).

Temperature Coefficient:

< (±0·04% ± 5 mA ) per ºC.

(2)

Slew Rate Ranges:

10 Ω range: 1 Ω per s to 100 Ω per ms.
400 Ω range: 40 Ω per s to 4000 Ω per ms.

Minimum transition time:

150 µs.

(3)

Constant Conductance Mode (CG)
Conductance Ranges:

<0·01 to 1 A/V (1 mA/V resolution)
and <0·2 to 40 A/V (0·01 A/V resolution).

Setting Accuracy:

± 0·5% ± 2 digits ± 30 mA.

Regulation:

< 2% for 90% load power change (V > 2 Volts, using remote sense).

Temperature Coefficient:

< (±0·04% ± 5 mA) per ºC.

(2)

(3)

Slew Rate Ranges:

1 A/V range: 0·1 A/V per s to >10 A/V per ms.
40 A/V range: 4 A/V per s to >400 A/V per ms.

Minimum transition time:

150 µs.

Constant Voltage Mode (CV)
Voltage Ranges:

V min to 8 V (1 mV resolution) and V min to 80 V (10 mV resolution).
V min depends on current: typically <100mV at 4A to <2V at 80A.

Setting Accuracy:

± 0·2% ± 2 digits.

Regulation:

< 30 mV for 90% load power change (using external sense).

Temperature Coefficient:

< (0·02% + 1 mV) per ºC.

(2)

(3)

Slew Rate Ranges:

8 V range:
80 V range:

Minimum transition time:

150 µs.

0·8 V per s to 80 V per ms.
8 V per s to 800 V per ms.

TRANSIENT CONTROL
Transient Generator
Pulse Repetition Rate:
Pulse Duty Cycle:
Setting Accuracy:

Adjustable from 0·01Hz (100 seconds) to 10kHz.
1% to 99% (percentage of period at Level A).
±1 %

Slew Rate Control
The slew rate control applies to all changes of level whether caused by manual selection, remote
control or the transient generator.
The level change is a linear slew between the two level settings. The range available in each
mode is shown above.
Setting Accuracy:

± 10% (on linear part of slope, excluding high frequency aberrations).

Variation in Level Settings:

± 5 digits of specified setting resolution for present mode and range.

Oscillator Sync Output
Connection:
Ratings:

Terminal block on rear panel. Opto-isolated open collector output
conducts during Level B phase of internal transient generator.
Max. off-state Voltage: 30V. On-state sink current: 2mA (typical).
5

DROPOUT VOLTAGE
The load will cease to conduct if the applied voltage falls below the Dropout Voltage setting;
active in all modes except Constant Voltage. The Dropout Voltage setting is also the threshold for
the Slow Start facility and acts as an offset voltage in Constant Resistance mode.
Setting Accuracy:

± 2% ± 20mV.

Slow Start
If Slow Start is enabled, the load will not conduct any current until the source voltage reaches the
Dropout Voltage setting; it will then ramp the controlled variable up (in CC, CP and CG modes) or
down (in CR and CV modes) to the Level setting at a rate determined by the Slew Rate setting.

METER SPECIFICATIONS
Display Type:

256 x112 pixel graphic LCD with white LED backlight.

Measured Values
Volts & Amps:
Watt & Ohms:
Voltage Accuracy:
Current Accuracy:

Measured values of current through and voltage across the load.
Power and equivalent load resistance, calculated from Volts and Amps.
± 0·1% ± 2 digits.
± 0·2% ± 3 digits.

CURRENT MONITOR OUTPUT
Output Terminals:
Output Impedance:
Scaling:
Accuracy:
Common Mode Range:

4mm safety sockets on front panel or terminal block on rear panel.
600Ω nominal, for >1MΩ load (e.g. oscilloscope).
50mV per Amp (4 Volts full scale).
± 0·5% ± 5mV.
(4)
± 3Vdc max. to load negative. A connection is required, see .

REMOTE CONTROL
Digital Remote Interfaces
The LD400P model provides LAN, USB, GPIB and RS232 interfaces for full remote control.
LAN:
USB:
GPIB:
RS232:

Ethernet 100/10base-T connection with auto cross-over detection.
1.4 LXI Core 2011 compliant.
Standard USB 2.0 connection. Operates as virtual COM port.
Conforming to IEEE488.1 and IEEE488.2.
Capabilities: SH1, AH1, T6, L4, SR1, RL2, PP1, DC1, DT0, C0, E2.
Standard 9-pin D connection. Baud rate: 9600.

External Control Input Characteristics
Connection:
Input Impedance:
Common Mode Range:

Terminal block on rear panel.
400kΩ each input to load negative.
± 100V to load negative.

External Analogue Voltage Control
Operating Mode:
Scaling:
Accuracy:
Common mode rejection:

The applied voltage sets the operating level within the selected range.
4 Volts full scale.
± 2% ± accuracy of selected range.
Better than –66dB.

External Logic Level (TTL) Control
Operating Mode:
Threshold:
6

The applied signal selects between Level A and Level B settings.
+ 1·5V nominal. A logic high selects Level B.

Remote Disable Input
Connection:
Threshold:

Terminal block on rear panel.
Input to the LED of an opto-isolator through 1kΩ resistor.
Apply >+3V to disable the load input. Max. Voltage 12V.

PROTECTION
Excess Power:

Protection Current:
Excess Current:
Protection Voltage:
Excess Voltage:

Temperature:
Sense Error:

The unit will attempt to limit the power to approx 430 Watts; if this fails
the unit will trip into the fault state at about 460 Watts. If intermittent
mode operation is enabled, these levels are 610 W and 630 W.
The input is disabled if the measured current exceeds a user set limit.
The unit will trip into the fault state at nominally 92 Amps.
The input is disabled if the measured voltage exceeds a user set limit.
The unit will conduct a current pulse (to absorb inductively generated
spikes) for 1ms at about 90V.
The unit will trip into the fault state at nominally 106V
Surge suppressors will start to conduct above 120V.
The unit will trip into the fault state if the heatsink temperature exceeds
safe levels.
The unit will trip into the fault state if the external voltage sense is more
than 6V below the internal sense.

GENERAL
AC Input:
Power Consumption:
Operating Range:
Storage Range:
Environmental:
Cooling:
Safety:
EMC:
Size:
Weight:
Option:

110V–120V or 220V–240V AC ±10%, 50/60Hz. Installation Category II.
30VA max. Mains lead rating: 6A minimum.
+ 5ºC to + 40ºC, 20% to 80% RH.
– 40ºC to + 70ºC.
Indoor use at altitudes up to 2000m, Pollution Degree 2.
Variable speed fan. Air exit at rear.
Complies with EN61010-1.
Complies with EN61326.
130mm H (3U) x 212mm W (½ rack) x 435mm D.
5.7 kg.
19-inch rack mount kit.

Specification Notes
(1)

In 600 Watt short-term operation mode the dynamic response is not specified, and both the
slew rate and the transient oscillator frequency range are restricted. The slew rate limitation
applies also to external voltage control. This mode is primarily intended for limited duration
operation at a fixed level setting.
(2)

Slew Rate Ranges refer to the theoretical slope of the transition between two levels,
regardless of whether that transition can be achieved when taking into account the level
difference, the set transition duration, the minimum transition time, and the characteristics of the
source.
(3)

Minimum Transition Time specification is an indication of the fastest available transition using
a benign source and low inductance connections, with a minimum terminal voltage of 5V and a
minimum current of 1A. The actual performance attainable with electronically regulated power
supplies depends on the combination of source and load loop bandwidths and interconnection
inductance.
(4)

The common mode capability of the current monitor is to provide tolerance of voltage drops in
cables. The monitor negative must be connected at some point to the load negative circuit.
7

EC Declaration of Conformity
We

Thurlby Thandar Instruments Ltd
Glebe Road
Huntingdon
Cambridgeshire PE29 7DR
England

declare that the

LD400 and LD400P DC Electronic Loads
Meet the intent of the EMC Directive 2004/108/EC and the Low Voltage Directive 2006/95/EC.
Compliance was demonstrated by conformance to the following specifications which have been
listed in the Official Journal of the European Communities.
EMC
Emissions:

EN61326-1 (2013) Radiated, Class B
EN61326-1 (2013) Conducted, Class B
EN61326-1 (2013) Harmonics, referring to EN61000-3-2 (2006)

Immunity:

EN61326-1 (2013) Immunity Table 1, referring to:
a)

EN61000-4-2 (2009) Electrostatic Discharge

EN61000-4-3 (2006) Electromagnetic Field

EN61000-4-11 (2004) Voltage Interrupt

EN61000-4-4 (2004) Fast Transient

EN61000-4-5 (2006) Surge

EN61000-4-6 (2009) Conducted RF

Performance levels achieved are detailed in the user manual.
Safety
EN61010-1 and EN61010-2-030 Installation Category II, Pollution Degree 2.

CHRIS WILDING
TECHNICAL DIRECTOR
10 September 2015

EMC
This instrument has been designed to meet the requirements of the EMC Directive 2004/108/EC.
Compliance was demonstrated by meeting the test limits of the following standards:

Emissions
EN61326-1 (2013) EMC product standard for Electrical Equipment for Measurement, Control
and Laboratory Use.
Test limits used were:
a)

Radiated:

Class B

Conducted: Class B

Harmonics: EN61000-3-2 (2006) Class A; the instrument is Class A by product category.

Immunity
EN61326-1 (2013) EMC product standard for Electrical Equipment for Measurement, Control
and Laboratory Use.
Test methods, limits and performance achieved are shown below:
(performance requirement shown in brackets):
a)

EN61000-4-2 (2009) Electrostatic Discharge: 8kV air, 4kV contact: Performance B (B).

EN61000-4-3 (2006) Electromagnetic Field:
3V/m, 80% AM at 1kHz, 80MHz – 1GHz: Performance A (A)
and 1.4GHz – 2GHz: Performance A (A);
1V/m, 2.0GHz – 2.7GHz: Performance A (A).

EN61000-4-11 (2004) Voltage Interrupt: ½ cycle and 1 cycle, 0%: Performance A (B);
25 cycles, 70%: Performance A (C); 250 cycles, 0%: Performance B (C).

EN61000-4-4 (2004) Fast Transient:
1kV peak (AC line), 0·5kV peak (Load connections): Performance B (B).

EN61000-4-5 (2006) Surge: 0·5kV (line to line), 1kV (line to ground): Performance B (B).

EN61000-4-6 (2009) Conducted RF: 3V, 80% AM at 1kHz, 150kHz – 80MHz:
AC line only (all other connections <3m, therefore not tested): Performance A (A).

According to EN61326-1 the definitions of performance criteria are:
Performance criterion A: ‘During test normal performance within the specification limits.’
Performance criterion B: ‘During test, temporary degradation, or loss of function or
performance which is self-recovering.’
Performance criterion C: ‘During test, temporary degradation, or loss of function or
performance which requires operator intervention or system reset occurs.’

Cautions
To ensure continued compliance with the EMC directive observe the following precautions:
a) After opening the case for any reason ensure that all signal and ground connections are
remade correctly and that case screws are correctly refitted and tightened.
b)

In the event of part replacement becoming necessary, only use components of an identical
type, see the Service Guide.

Safety
This instrument is Safety Class I according to IEC classification and has been designed to meet
the requirements of EN61010−1 (Safety Requirements for Electrical Equipment for
Measurement, Control and Laboratory Use). It is an Installation Category II instrument intended
for operation from a normal single phase supply.
This instrument has been tested in accordance with EN61010−1 and has been supplied in a safe
condition. This instruction manual contains some information and warnings which have to be
followed by the user to ensure safe operation and to retain the instrument in a safe condition.
This instrument has been designed for indoor use in a Pollution Degree 2 environment in the
temperature range 5°C to 40°C, 20% −80% RH (non−condensing). It may occasionally be
subjected to temperatures between +5° and −10°C without degradation of its safety. Do not
operate while condensation is present.
Use of this instrument in a manner not specified by these instructions may impair the safety
protection provided.
The unit does not have a fuse in the load circuit: if the source connected to the load is
capable of generating substantial currents in the event of a fault, users should assess the risks
involved and consider the inclusion of an appropriate fuse, circuit breaker or switch in the
connection between the source and this load.
Do not operate the instrument outside its rated supply voltages or environmental range.
WARNING! THIS INSTRUMENT MUST BE EARTHED
Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited. The protective action must not be
negated by the use of an extension cord without a protective conductor.
When the instrument is connected to its supply, terminals may be live and opening the covers or
removal of parts (except those to which access can be gained by hand) is likely to expose live
parts. The apparatus shall be disconnected from all voltage sources before it is opened for any
adjustment, replacement, maintenance or repair.
Any adjustment, maintenance and repair of the opened instrument under voltage shall be
avoided as far as possible and, if inevitable, shall be carried out only by a skilled person who is
aware of the hazard involved.
If the instrument is clearly defective, has been subject to mechanical damage, excessive
moisture or chemical corrosion the safety protection may be impaired and the apparatus should
be withdrawn from use and returned for checking and repair.
The instrument contains both encapsulated fuses and non-resetting thermal fuses; these are not
replaceable by the user. The short-circuiting of these protective devices is prohibited.
Do not wet the instrument when cleaning it.
The following symbols are used on the instrument and in this manual:−
Caution refer to the accompanying documentation,
incorrect operation may damage the instrument.
Alternating Current.
mains supply OFF.

mains supply ON.

Installation
Mains Operating Voltage
The operating voltage of the instrument is shown on the rear panel. Should it be necessary to
change the operating voltage from 230V to 115V or vice-versa, proceed as follows:
1.
2.
3.
4.
5.

6.
7.
8.

Disconnect the instrument from all voltage sources, including the mains and all inputs.
Remove the screws which hold the case upper to the chassis and lift off.
Unplug all cable connectors from the power supply PCB (don’t pull on the wires).
Remove the five nuts which hold the power supply PCB in place, and lift it off the studs.
Fit the soldered links (alongside the transformers) for the required operating voltage:For 230V fit only LK2 and LK5
For 115V fit only LK1, LK3, LK4 and LK6.
These links may be either tinned copper wire or zero-ohm resistors.
Refit the power supply PCB, ensuring that no wires are trapped. Check that all cables are
correctly connected and that all five nuts are sufficiently tightened.
Refit the case upper.
To comply with safety standard requirements the operating voltage marked on the rear
panel must be changed to clearly show the new voltage setting.

Mains Lead
Connect the instrument to the AC supply using the mains lead provided. Should a mains plug be
required for a different type of mains outlet socket, use a suitably rated and approved 3-core
mains lead set which is fitted with the required wall plug and an IEC60320 C13 connector for the
instrument end. This instrument requires a lead rated at 6A for all mains supply voltages.
WARNING! THIS INSTRUMENT MUST BE EARTHED
Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited.

Mounting
This instrument is suitable both for bench use and rack mounting. It is delivered with feet for
bench mounting. The front feet include a tilt mechanism for optimal panel angle.
A rack kit for mounting one or two of these half-width 3U high units is available from the
Manufacturers or their overseas agents; a blanking piece is also available for unused positions in
the rack.

Ventilation
The unit is cooled by a variable speed fan which vents at the rear. Take care not to restrict the air
inlets at the top, side and bottom panels or the exit at the rear. In rack-mounted situations allow
adequate space around the instrument and/or use a fan tray for forced cooling.
If ducting is applied to the air outlet, additional extraction is required.

Fuses
Most fuses in this instrument are not user replaceable. The exception is an internal fuse on the
power supply PCB, which is intended to protect the unit from the accidental connection of 230V
mains supply to a unit configured for 115V operation. Before replacing this fuse, ensure that the
unit is configured correctly, as described above.
The replacement fuse must be a 20x5mm 500mA (T) 250Vac rated HBC (ceramic tube) type.

Connections
Front Panel Connections
Load Input
The INPUT terminals for the load circuit on the front panel accept 4mm plugs into the end, 2mm
diameter wire into the cross hole, or ¼ inch spade connections. Their maximum current rating is
30 Amps. For higher currents (or lower circuit resistance) use the rear panel terminals; do not
use both simultaneously.
The load circuit is isolated from ground, and potentials up to ± 300 Volts DC to ground are
allowed, but it is essential to observe safe insulation practice.
Ensure that the source is connected with the correct polarity.
The maximum current through these terminals is 30 Amps.
The maximum voltage allowed across the load is 80 Volts.
The unit does not have a fuse in the load circuit: ensure that the maximum
prospective fault current is limited to a safe level, see below.

Current Monitor Output
The Current Monitor terminals provide a voltage proportional to the load current flowing with a
scaling factor of 50 mV per Amp (4 Volts for 80 Amps full scale). The output impedance is
nominally 600Ω and the calibration assumes a high impedance load such as an oscilloscope.
A differential driver allows a common mode range of ± 3 Volts between the negative
monitor terminal and the negative load terminal. The output will be inaccurate (and the
unit may be damaged) if voltages exceeding this are applied.
The common mode capability is intended to accommodate any voltage drop in the load circuit
cables and to avoid difficulties with current loops. There should be an external connection
between the monitor negative and the load negative at some point in the circuit, wherever is most
convenient, except this is not normally necessary for a battery powered portable DMM.

Rear Panel Connections
Load Input
The INPUT terminals for the load circuit on the rear panel accept 4mm plugs into the end (4mm
plugs have a current rating of 32 Amps or less), 5mm diameter wire into the cross hole or 8mm
spade connections (with a maximum blade width of 16mm).
The wiring and connection arrangement must be capable of supporting the current required; for
80 Amps, 16mm2 cable is needed.
The load circuit is isolated from ground, and potentials up to ± 300 Volts DC to ground are
allowed, but it is essential to observe safe insulation practice.
Ensure that the source is connected with the correct polarity.
The maximum current through these terminals is 80 Amps.
The maximum voltage allowed across the load is 80 Volts.
The unit does not have a fuse in the load circuit: ensure that the maximum
prospective fault current is limited to a safe level, see below.

Prospective Fault Current Protection
This unit is not intended to act as an overcurrent fault protection device for the source being
tested. If the source itself also does not include suitable overcurrent protection, and is capable of
generating substantial currents in the event of a fault, users should assess the risks involved and
consider the inclusion of an appropriate fuse, circuit breaker or easily accessible switch in the
connection between the source and this load.
12

Terminal Blocks
All other rear panel connections are made via the screw-less terminal blocks. To make
connections to the terminal blocks, use a flat screwdriver to press the spring-loaded orange
actuator inwards to open the wire clamp; insert the wire end fully into the hole and release the
actuator. Ensure the wire is properly gripped. Take care to observe the marked polarity.

Current Monitor Output
The top pair of terminals, marked CURRENT MONITOR, provide the current monitor output.
They are wired in parallel with the front panel Current Monitor sockets and the same
requirements apply, see above.

Remote Control Voltage Input
The CONTROL VOLTAGE terminals are used in two operating modes of the instrument:
In EXTERNAL VOLTAGE mode an analogue signal applied here sets the level of the load; the
scaling is 4 Volts full scale.
In EXTERNAL TTL mode, a logic signal applied here selects either the LEVEL A setting (logic
low) or the LEVEL B setting (logic high). The switching threshold is nominally +1·5V.
These terminals will tolerate a common mode voltage of up to ±100 Volts relative to
the negative terminal of the load input. The input impedance is 400kΩ from each
terminal to the load negative, so a common mode current will flow.

External Voltage Sense Input
To avoid errors in sensing the voltage of the source caused by voltage drops in the high current
wiring, connect the EXTERNAL SENSE terminals to the external circuit at the point where the
voltage needs to be measured (normally at the output terminals of the source under test). Move
the VOLTAGE SENSE SELECT slide switch on the rear panel to the EXT position.
Ensure that the source is connected with the correct polarity.
These terminals must not be connected to any voltage other than the source that is
connected to the load input.

Remote Disable Input
Apply greater than +3V (preferably +5V) to the DISABLE INPUT terminals to disable the load
input; these are the input to an opto-coupler, through 1kΩ, and are galvanically isolated from all
other terminals. The input current is less than 2·5mA at 5V.
The maximum input voltage is +12Vdc. Avoid reverse polarity.

Oscillator Sync Output
The SYNC OUTPUT is an open collector output of an opto-coupler driven by the signal from the
internal oscillator; it is galvanically isolated from all other terminals. A suitable pull-up resistor and
power supply (e.g. 4·7kΩ to +5V) are needed to generate a usable signal, which could be used
to trigger an oscilloscope. There is a 1kΩ series protection resistor.
The maximum collector supply voltage is +30Vdc. Avoid reverse polarity.
The load resistor should be chosen to source ideally 1mA, maximum 2mA.

Digital Remote Control Connections
The LD400P model provides full remote control capabilities through standard LAN, USB, GPIB
and RS232 interfaces. All of these are isolated from the load input terminals of the unit. The USB,
GPIB and RS232 interfaces are connected to chassis ground, and care must be taken to avoid
introducing ground loops. The LAN interface is isolated by standard network transformers.
Full details are given in the ‘Remote Interface Configuration’ chapter later in this manual.
13

Initial Operation
This instrument provides a controllable DC load (a power sink) intended for testing all forms of
DC power supply including batteries, photo-voltaic cells, fuel cells, turbines and generators as
well as electronic power supply units.

Organisation of this manual
The paragraphs below are intended to briefly introduce the particular features of this instrument
and the terminology used in this manual. More technical details are given in later chapters of the
manual.
The next chapter describes the general operation of the front panel and its display, followed by
full instructions for setting each parameter. A short chapter then describes the Analogue Remote
Control facilities, including level selection by a logic level signal.
Following that there is a chapter giving some application notes and implementation details, which
gives more information on some practical difficulties which may occasionally be encountered in
each operating mode, together with some advice on mitigating strategies.
Finally the digital remote control interfaces and command set of the LD400P programmable
version of the instrument are covered.

Load modes
The power dissipating stage in this load is fundamentally an adjustable current sink, which
conducts a current that does not depend on the voltage presently applied from the source being
investigated. This is known as Constant Current operation.
An analogue multiplier is used to offer other operating modes in which the current does depend
on the applied voltage in a known way, providing a choice of Constant Power, Constant
Resistance, or Constant Conductance characteristics. A fifth mode, Constant Voltage, operates in
a completely different manner to adjust the current to whatever value is needed to obtain the
desired voltage from the source.

Constant and Transient Operation
The load offers two independent level settings, referred to as Level A and Level B. Two keys
marked A and B in the LEVEL SELECT area of the front panel allow the choice of which level is
active.
Transient changes in the magnitude of the load are generated by switching between the two
levels. The transition between the two is a straight line at a slew rate that is specified by the user.
The switching between the two levels can be controlled either by an internal transient oscillator,
which has adjustable frequency and duty cycle, or an external logic (TTL level) signal.
There is no restriction on which of the two levels is the larger.

Dropout voltage
The primary purpose of the dropout facility is to protect batteries from being excessively
discharged. When the source voltage falls below the Dropout threshold voltage setting, the load
will reduce the current it draws, eventually to zero. This is a dynamic limit, not a latched state, so
if the source voltage recovers above the threshold (as batteries often do) then the load will
conduct current again.

Slow Start
The slow start facility causes the current taken by the load to rise gently, at the rate determined
by the slew rate setting, when the load is enabled or when the source voltage rises above the
Dropout Voltage threshold setting. It also causes the current to fall at the same rate when the
load input is disabled. This facility is particularly useful in Constant Power mode, to avoid a
latch-up condition when the source is started; see the ‘Application Notes’ chapter for details.
14

Short Term Operation up to 600 Watts
The instrument has provision for applications which require the dissipation of higher than normal
powers for a limited period of time. It imposes a limit on the combination of power and time by
first displaying a warning message and then disabling the input. Full details of the constraints that
apply to this mode are given later, on page 24.

Voltage and Current Limit Conditions
The unit has provision for the user to specify limits on the permitted measured value of voltage or
current. If either of these limits is exceeded then the input will be disabled.

Power Limit
The unit continuously monitors the internal power dissipation and varies the speed of the fan
accordingly. If the dissipation rises above about 430 (or 610) Watts, a hardware power limit circuit
will come into operation and attempt to constrain the load current to control the dissipation. The
unit is then operating in a non-linear mode, which will change the stability conditions. If the power
limit circuit fails to prevent the power rising above a slightly higher fault threshold (perhaps
because of instability) then the fault detector will be tripped and the load will cease to conduct.

Input Condition Lamps
Two lamps above the Input Enable switch indicate the operating state of the unit. They are both
off when the input is disabled. The green lamp lights when the input is enabled, and if the load is
operating normally then the yellow lamp will not be lit.
The yellow lamps lights if the load cannot conduct the required current, with a message on the
status line at the top right of the display distinguishing between the three possible reasons:
• High Power: the power limit circuit is operating as described above.
• Dropout: the voltage applied from the source is below the setting of the Dropout voltage.
• Low Voltage: the power stage is in the minimum resistance condition, because the
voltage available from the source is insufficient to maintain the current level required.
The minimum resistance condition will occur either if the source is switched off and is not
providing any voltage at all, or if the voltage drop across the connection leads is causing the
actual input voltage at the load to be below its minimum operating level. Note that if the source
voltage is suddenly applied while the load circuit is in this state, then a current transient will
probably occur.
If only the yellow lamp is lit, with the green lamp off, then a persistent fault condition exists.

Fault Conditions
The unit detects (in hardware) the following fault conditions:
• Current above about 92 Amps.
• Power in excess of about 450 (or 630) Watts (that the power limit circuit has not
succeeded in controlling to the lower threshold as described above).
• Voltage above about 106 Volts.
• Excessive difference between external and internal voltage sense values.
• Excessive heatsink temperature.
• Fan failure.
The fault detectors for excess current, power and voltage have filter networks with a
time-constant of a few milliseconds to allow brief transients to be handled.
When any of these fault conditions occurs, the input is disabled, so the unit will cease to conduct
current and a fault message will be displayed. An excessive current or power condition will
disappear as soon as the input is disabled, but any of the other conditions will cause the yellow
lamp only to remain lit, and the message Fault to show on the status line, until it is cleared.
15

Connecting the Load to the Source
The INPUT terminals of the load must be connected to the source to be tested using sufficiently
low resistance and low inductance connections. Inductance in the interconnection can have a
significant adverse impact on the stability of the source and load combination. The wiring should
be as short and as thick as possible. It is essential that the voltage drop across the connecting
leads is sufficiently less than the source voltage to leave enough working voltage across the load.
This requirement must be met at the load input terminals even if external sensing is employed.
The front panel terminals may be used for currents up to 30 Amps; for higher currents the rear
panel terminals must be used.
The load terminals of the instrument are floating from ground, and may be used at potentials of
up to ± 300 Volts DC from ground. Connection to any AC mains circuit is not permitted. Ensure
that all wiring is safely insulated for the working voltage involved.

Prospective Fault Current
The instrument detects any fault condition and responds by disabling the load by turning off the
power devices. However there is no internal fuse in the load circuit, so the possibility exists of a
high current passing if the external source applies a condition so far beyond the rating of the unit
that a power FET is destroyed, which can sometimes result in the device becoming a short
circuit. If the source is capable of supplying a dangerous level of prospective fault current, and
does not itself contain a fuse or circuit breaker, or cannot be easily turned off, users should
consider adding an external fuse to the circuit, particularly if unattended operation is likely.

External Voltage Sensing
When the load is conducting current there will be a voltage drop in the connecting leads. In order
to obtain the expected load characteristic in any mode other than Constant Current, external
voltage sensing leads should be connected from the terminals of the source to the external sense
inputs on the rear panel of the load. In Constant Current (CC) mode external voltage sensing only
improves the accuracy of the meter readings; it does not affect the behaviour of the load.
To avoid impact on the stability margin do not add phase shift in the sensing circuit; in particular,
the use of decoupling capacitors should be avoided. If the sensing connections are likely to be
subject to RF or magnetic fields, use twisted pair cable with an overall shield. The shield should
be grounded or connected to load negative.
The rear panel VOLTAGE SENSE SELECT switch selects between INT (internal) and EXT (external)
voltage sensing. Note that the internal sensing circuit is always used for the power and voltage
protection circuits.
Caution: The unit is designed to permit up to 6 Volts difference between internal and external
sensing (in order to permit zero voltage operation using an offsetting battery); if this switch is in
the EXT position, but the sense terminals are not connected, the unit will not detect the fault
condition until the source voltage exceeds this value. This can result in unexpected operation.

Remote Input Disable
This input is provided for remote override of the INPUT ENABLE function of the load, possibly for
safety reasons. It is available in all operating modes of the instrument. It is a fully floating input to
an opto-isolator: apply 3 to 12 volts (observing polarity) to disable the load. The load is only
enabled if this signal is absent and the input has been enabled with the front panel controls.

Switching On
The line POWER (
) switch is at the bottom left of the front panel. Before switching on ( l ),
check that the line operating voltage of the unit (marked on the rear panel) is suitable for the local
supply. After switching the power on ( l ) the LCD should light and display firmware version
information. Avoid turning off the power until the instrument is fully initialised and the home
screen is displayed.
16

Front Panel Operation
In this manual, front panel labels are shown as they appear, in capitals, e.g. LEVEL SELECT.
Individual key names are shown in bold, e.g. Transient, and the blue soft-keys are referred to by
their present function, as labelled on the bottom line of the display, shown in bold italics, e.g.
Recall. Text or messages displayed on the LCD are shown in bold, e.g. Enabled, Utilities.

Keys and ∆ Adjust
The front panel keys are divided into four areas. The numeric keys and the blue keys below the
display are used to configure the instrument through the menu structure described below. The CE
key cancels the last numeric keystroke while the Home key cancels an entire menu selection and
returns to the home screen. The Home key is also used for the ‘return to local’ request from
digital remote control.
The three LEVEL SELECT keys (A, B and Transient) determine which of the two level settings is
active, or engage the transient mode which switches between them. The associated lamps
indicate the presently active state; these keys are also used to return from external analogue
control to manual selection.
The ∆ ADJUST knob and its three associated keys (Levels, Off and Transient) are used to
choose and modify the existing value of any one of the numeric parameters of the instrument.
The ENABLE key in the INPUT section (referred to as the INPUT ENABLE key) controls the load,
with alternate presses switching between the conducting and non-conducting conditions. The
green lamp shows if the input is enabled; the yellow lamp reports if the power stage is saturated,
as described in the paragraph ‘Input Condition Lamps’ in the ‘Initial Operation’ chapter above.

The Display and the Home Screen
All parameter settings and meter readings are shown on the backlit liquid crystal display (LCD).
At power up the instrument initialises to the home screen, which is the normal display during
operation of the unit. This screen displays all of the load meter readings and the most important
load parameter settings as described below, and is also the top level of the soft-key driven menu
structure. The display changes to show other screens as selections are made to enter parameter
values and then returns to the home screen when entry is complete.

Status Line
The status line of the instrument is visible along the top of the display at all times except when
one of the store, recall or utilities menus is being shown. It indicates the current status of the
instrument as follows (in order, from left to right across the display):
•

The load mode field indicates the present load mode – CC, CP, CR, CG or CV.

•

Slow is displayed when slow start operation has been enabled.

•

Slew is displayed as a warning when the present slew rate setting is too slow with
regards to the level difference, transient frequency and duty cycle, see ‘Slew Rate Error
Conditions’ (on page 23 below).

•

Lim is displayed when either of the user defined current or voltage limits is enabled.

•

The level select field (in the centre) indicates which input level or control method is
currently selected – Level A, Level B, Transient, Ext V or Ext TTL.

•

The LAN field indicates the status of the Local Area Network (if fitted). When there is no
LAN connection the field displays . While a connection is being established the
and , and then while connected the field will show .
indicator will flash between
See the ‘Remote Interface Configuration’ chapter for more information.

•

The input status field (at the right hand end) indicates the instrument’s present load input
condition – Disabled, Enabled, Low Voltage, Dropout, Power Limit or Fault, as
described in the paragraph on ‘Input Condition Lamps’ (on page 15) above.
17

Home Screen Data
Below the status line are the meter displays which show the actual measured source voltage and,
once the load is enabled, the load current. Below this, the screen is divided into three areas. On
the left, under the heading METERS, the display shows the present power in the load and the
equivalent resistance; these values are computed from the measured voltage and current
readings. Any of these meter displays will show HIGH (or MAX for power) if the measured value
is beyond the capabilities of the unit.
In the centre, under the heading LEVELS, the display shows the present settings for Level A and
Level B (the units depend on the operating mode) and the Dropout Voltage setting.
On the right, under the heading TRANSIENT, the display shows the settings for the Frequency
and Duty cycle of the internal oscillator, and the Slew Rate of the transitions.
All six of these parameters can be modified either by direct numeric entry or by using the knob to
increment or decrement the present value as described below.

Soft-Keys
The soft-keys are the six blue keys found directly below the LCD. The function of each of these
keys changes as the instrument is operated. The available function is shown on the bottom line
of the display in a tab above each key. If any of the keys have no functionality in a particular
menu then the tab is lowered to show it is inactive.
On the home screen there are two sets of soft-key functions available; the right hand key,
alternately labelled More > or More < switches between the two. All additional menus are
accessed through the soft-keys in one of these sets.
The major parameters accessible in the first set are:
Mode

To select the operating mode.

Limits

To impose cut-off limits on the applied voltage or current values,
or to enter the 600 Watt short term operation mode.

Level

To enter numeric values for Level A and Level B.

Dropout

To enter a numeric value for the Dropout Voltage.

Transient

To access a second level to set-up the transient functionality.

The second set includes:
Store & Recall

To setup, review and use saved settings of the unit.

Extern

To enable or disable analogue remote control of the level, or logic (TTL)
level selection between the two levels, as described in the chapter on
‘Analogue Remote Control’.

Utilities

To configure some secondary facilities of the instrument and to set
parameters of the remote interfaces.

The Transient second level menu (when selected from the first set above) includes:
Freq

To enter a numeric value for the Frequency of the internal oscillator.

Duty

To enter a numeric value for the Duty cycle of the internal oscillator.

Slew

To enter a numeric value for the Slew Rate of the transitions.

Slow

To enable or disable the Slow start and stop facility.

On most of the lower level menus, the left hand key, labelled Back or Cancel, can be used to
return to the previous menu. This allows exploration of the various menus without risk of putting
the unit into unexpected configurations. Back returns to the previous menu, keeping any
changes that have been made in the current menu, while Cancel (if offered) will undo any
change made before reverting to the previous menu. The Home key reverts directly to the home
screen and the top level of the menu structure (also abandoning any incomplete value entry).
18

General Numeric Entry of Parameters
All user modifiable load parameters can be set using the numeric keypad. The desired parameter
is first selected from the menu using the soft-keys. The display then changes to show the
parameter entry screen which indicates the name of the parameter, its present value prior to
editing, and in most cases the entry limits and resolution. A message prompting for the entry of
the new value is shown. When any number key is pressed this prompt is removed and replaced
by the new value being constructed, and the soft-key labels change to show a list of units
applicable to the parameter being edited. The CE key deletes individual keystrokes; alternatively
the entire entry may be cancelled by pressing either the Home key or the Cancel soft-key.
Once the number entry is complete it must be terminated by pressing the required units soft-key
(choosing A or mA, for example). The value is then checked against the parameter limits and, if it
falls within the allowed range, it is accepted and immediately implemented as the new value for
that parameter. If the value does not fall within the permitted range then an error message is
displayed and the buzzer will sound. If applicable the entry may be rounded to fit within the
specified parameter resolution.
Paragraphs below describe particular features associated with each parameter.

Variation of Parameter Values using ∆ Adjust
The level and transient parameters of the load can be adjusted by incrementing or decrementing
the present value using either the knob or soft-keys.
Note: this adjustment mechanism is only available whilst the instrument is on the home screen.
Two keys above the knob, labelled Levels and Transient, select the parameter to be modified
and initiate the adjustment. Pressing the Levels key initially selects Level A; a second press
selects Level B and a third press selects the Dropout Voltage setting. The cycle can be repeated
if required. Similarly, multiple presses of the Transient key select between Frequency, Duty Cycle
and Slew Rate. A lamp above each of these keys blinks whilst adjustment is enabled and four
cursor soft-keys are shown.
The display of the selected parameter value is expanded to fill its edit box, with an adjustment
indicator ( ) positioned under the digit to be varied. The ◄ and ► soft-keys can be used to select
which digit position will be adjusted, and then either the knob or the ▲and ▼ soft-keys can be
used to increment or decrement the value at that position. Digits to the left of the one being
varied are automatically incremented or decremented when the decade overflow or underflow
point is reached. Digits to the right of the one being varied always remain unchanged unless a
point of decade resolution change is reached, in which case digits to the right may be lost
through truncation. If the least significant digit is being incremented and a decade resolution
change is reached, the new least significant digit becomes the one being adjusted.
Each change made is applied immediately, so long as the value remains within the permitted
limits of that parameter. If an increment or decrement of the current position would exceed a
range limit then the parameter value remains unchanged; partial adjustments are not made.
Pressing the Off soft-key or the Off key above the knob (or the Home key) ends the adjustment,
retaining the new value, and returns the display to the home screen. Pressing the Cancel softkey ends the adjustment and restores the last parameter to the value it had when it was selected
for adjustment.

Configuring the Load
The normal sequence of operation is to select the load Mode, set the required operating Level
and Dropout Voltage, and then Enable the input. If transient operation is required, the second
Level setting and the Slew Rate parameters must be set, as well as the frequency and duty cycle
of the internal oscillator if it is to be used.
The home screen shows all the parameter settings, which can be viewed before the input is
enabled. All parameters except load Mode and level Range can be adjusted as required while the
19

input is enabled. Changing either the load mode or the level range while the input is enabled will
trip a fault detector and cause the input to be disabled before the change is implemented.

Selection of Load Mode
The first action in configuring the unit for a particular application is to choose the load mode,
which determines how the current drawn by the load varies with the applied voltage (V). The
Mode soft-key on the home screen opens a menu offering the various modes listed in the table
below. More detailed descriptions of the properties of each mode are given in the ‘Application
Notes’ chapter later in this manual.
Changing the mode requires the load input to be disabled, which will be done automatically if not
already done by the user. The display returns to the home screen as soon as a mode is selected.
The available operating modes are:
CC

Constant Current

The current is the Level setting, independent of voltage.

Constant Power

Implements I = W / V where W is the Level setting.

Constant Conductance

Implements I = V * G where G is the Level setting.

Constant Resistance

Implements I = (V – V dropout ) / R where R is the Level
setting and V dropout is the Dropout Voltage setting.

Constant Voltage

The load sinks whatever current is necessary to maintain
the terminal voltage equal to the Level setting.

Level A and Level B Setting and Range Selection
Pressing the Level soft-key on the home screen initially opens the level setting prompt for either
Level A or Level B, depending on which was altered last. The right hand soft-keys, labelled
A SET and B SET, can be used to switch the prompt to the other level. If the level being edited is
not currently active in controlling the load, a Select soft-key will appear allowing it to be made the
active selection if required. A new numeric value can be entered as described above. Separate
settings for both level values are retained for each operating mode.
There are two ranges for level setting in each of the load operating modes except constant
power. These differ in both the range of values permitted and the entry resolution; the present
values are shown in the number prompt. Pressing the Range soft-key opens the range selection
menu, with the presently active range highlighted. The selection can be changed using either the
▲ or ▼ soft-keys or the knob. Pressing the OK soft-key implements the new selection. Changing
the range requires the load input to be disabled, which will be done automatically if not already
done by the user. Alternatively pressing the Cancel soft-key leaves the range unchanged. In
either case the instrument returns to the level setting menu. Changing from a high resolution
range to a low resolution range may result in the truncation of the set level. If the range is
changed and the set level value exceeds the limits for the new range, the value is updated to the
maximum or minimum of the new range.
The level setting menu remains on screen, allowing further changes to be made, until either the
Back soft-key or the Home key is pressed to return to the home screen.

Dropout Voltage
Pressing the Dropout soft-key on the home screen opens the Dropout Voltage setting prompt. In
the usual way this displays the present Dropout Voltage setting, the range in which the new value
can be set, and the maximum resolution of the setting. After entry of the number press either the
mV or V soft-key to implement the setting. Either the Back soft-key or the Home key returns the
display to the home screen.
The primary purpose of the dropout voltage setting is to protect batteries from excessive
discharge. The load will cease to conduct current when the applied voltage from the source falls
below this setting. Note that this is a dynamic limit, not a latching condition, so if there is any
wiring resistance between the source and the voltage sensing point of the load then there will be
20

a soft entry into the dropout condition – the series voltage drop will reduce as the current starts to
fall, so raising the voltage measured by the load. Batteries may also recover as the load is
reduced, raising the voltage back above the dropout threshold so the load resumes conduction.
There is a possibility of hunting or instability in this operating condition. The front panel lamp will
show yellow and the status line report Dropout when the dropout circuit becomes active.
The Dropout Voltage setting has a special effect in Constant Resistance (CR) mode, when it
provides a starting point for the constant resistance characteristic (see the description in the
‘Application Notes‘ chapter for more detail). The Dropout facility is not available in Constant
Voltage (CV) mode as it conflicts with the basic intention of that mode.
The Dropout Voltage setting is also used as the threshold for the Slow Start circuit (see below).
If the dropout facility is not required, set the Dropout Voltage to 0 Volts. The status line will show
Dropout as a warning whenever this setting is above 0V and no current is being drawn.

Slow Start
The purpose of the slow start circuit is to ramp the demand of the load up slowly from zero to the
final value. The rate of rise is determined by the Slew Rate setting. The ramp starts either when
the Input is Enabled, or when the voltage from the attached source passes the level of the
Dropout Voltage setting. When the Input is Disabled the demand will ramp back down to provide
a slow stop (assuming, of course, that the source voltage remains active).
The setting for this facility is on the Transient menu, so first press the Trans soft-key on the
home screen to enter the Transient menu, and then press the Slow soft-key on that menu to
access a soft-key to alternately enable or disable slow start. While it is enabled, Slow will appear
on the status line of the instrument. Press the Back soft-key to return to the transient menu or
the Home key to return directly to the home screen.
In CP (constant power) mode the slow start facility will almost always be needed, to avoid the
lock-up condition that will occur at low voltages (when attaining the desired power requires a high
current) if the source does not have sufficient current capability to reach the power level
demanded. See the ‘Application Notes’ chapter later for a discussion of some of the implications
of the fact that constant power mode causes the load to act as a negative resistance.
In CR (constant resistance) mode the load will start at the maximum Ohms level of the active
range and ramp down to the final Ohms value. Because the initial resistance is not infinite there
will be an initial current step before the ramp starts when the load becomes active. Note also that
a linear slew in Ohms is not a linear slew in Amps if the source voltage is constant.
In CV (constant voltage) mode the setting will start at the maximum Voltage level of the active
range and ramp down to the final Voltage value. The load will not start to conduct current until the
setting ramps down past the open circuit voltage of the attached source. After this the current will
increase at a rate determined by the characteristics of the source and its effective output
resistance, until the set-point voltage is reached. If the source enters a constant current mode
then the load cannot impose a slow current ramp.

Introduction to Transient Operation
The unit includes the capability of generating load transients, which are intended to help in
testing the transient response of a source. Transient operation is available in all operating modes.
A transient is an alternation between the Level A and Level B settings, with the transition between
the two levels being a straight line (in the controlled variable of the active mode) whose slope is
determined by the Slew Rate setting. Note that the transient is specified by setting the two
absolute levels, not the difference between them (as is the case with some electronic loads).
There is no limitation on which of the two levels is the larger.
Transients can be timed either by an internal oscillator or by an external TTL signal (see the
description of the Extern menu on page 27 below). Transient operation controlled by the internal
oscillator always starts with the Level A setting, including a transition from Level B if required. The
oscillator starts when the last of the three required conditions occurs: either when the input is
21

Enabled, or when the Transient level control key is selected, or (if the slow start circuit is active)
when the source voltage rises above the Dropout Voltage threshold.
It is also possible to use the External Analogue Voltage control mode to generate transients of
any required shape by using an external generator to produce the required waveform. This is
also controlled by the Extern menu (page 27). Note that the external signal still passes through
the internal slew rate control circuits, so appropriate Slew Rate settings need to be made.
To end Transient operation (whether internal or external) and return to a constant level press
either the A or B key (in the LEVEL SELECT section) as required.

Transient Menu
Press the Trans soft-key on the home screen to enter the Transient menu which gives access to
the controls for the Frequency and Duty Cycle of the internal oscillator and the Slew Rate
settings which apply to all changes in level, however caused.
These parameters can also be changed using the ∆ ADJUST facilities described previously, but to
do this the unit must be on the home screen not the Transient menu.
Note that changes to the transient frequency or duty cycle do not take effect until the end of the
present cycle, at the return to Level A. This is particularly noticeable at very low frequencies.
Disabling and then re-enabling the load input will also immediately start a new cycle.

Transient Frequency
The repetition rate of the internally timed transients can be set in terms of frequency or period.
Pressing the Freq or Period soft-key on the Transient menu opens the Frequency and Period
setting menu. A new value can be entered, in the present representation, in the usual manner.
Two soft-keys labelled Freq and Period allow the alternative representation to be chosen. Press
the Back soft-key to return to the transient menu or the Home key to return to the home screen.
The soft-key label on the transient menu will show either Freq or Period to reflect the most
recent choice of representation.

Transient Duty Cycle
Pressing the Duty soft-key on the Transient menu opens the Duty cycle setting menu. This
setting specifies the percentage of each repetition spent at the Level A setting, including the
transition from Level B to Level A; the transition back to Level B and the time stable at that
setting occupies the remainder of the cycle.
The available duty cycle range is 1% to 99%, but note that the time duration of each portion of
the cycle must be sufficient for the transition defined by the Slew Rate and Level settings to
occur; otherwise the load will never reach the steady state at the set value before the next
transition in the opposite direction starts. This error condition is discussed below. Press the Back
soft-key to return to the Transient menu or the Home key to return to the home screen.

Slew Rate
Pressing the Slew soft-key on the Transient menu opens the Slew Rate setting menu. This Slew
Rate setting sets the slope of the transitions between the two level settings. It applies to all
changes in level whether caused by manual setting, adjustment using the knob, the internal
transient generator or external voltage control. It is also used to determine the rate of rise and fall
when the Slow Start circuit is triggered.
The slew control circuit introduces a small additional error into the accuracy of the level settings,
which varies depending on the actual Slew Rate setting. If the dynamic facilities of the load are
not being used, then the Default soft-key sets the circuit to the calibrated state for best accuracy.
The circuit provides a linear transition in the control value of the active mode, so, for example, in
Constant Power (CP) mode the slew rate is expressed in Watts per microsecond, Watts per

millisecond or (at very slow rates) Watts per second. The shape of the current transition is
therefore not necessarily linear in any mode other than Constant Current (CC).
In addition to the usual numeric prompt this menu also shows the calculated theoretical transition
time considering the present Slew Rate setting and the difference between Level A and Level B.
This theoretical value takes no account of any dependency of the actual transition time on the
source and load characteristics, impedances and interconnection inductance which may occur,
particularly at fast slew rates. The user must ensure that the transition time which results from the
values entered is not shorter than the minimum attainable transition time in the present mode,
which is documented in the Specification. It is emphasised that severe overshoots can occur if
the slew rate is set faster than the combination of source and load is capable of supporting
(which may be slower than the value in the Specification, which applies to optimal conditions),
see the section on ‘Fast Slew Rate Limitations’ below.
Pressing the Range soft-key produces a display of the limits of available slew rate for the present
operating mode and range. If a slew rate value is entered that falls outside the parameter limit
range, an error message is displayed, followed also by a display of these range limits.
The bandwidth of the power stages of the load is reduced (by changing the compensation
networks) when the slew rate is set to less than 0·1% of the maximum slew rate for the given
load mode and range. For example, on the 80A range in constant current mode, the maximum
slew rate setting is 2.5A/us, so the bandwidth is reduced when the slew rate is set < 2.5A/ms.
This change is made even if the transient facilities are not being used, and alters the dynamic
behaviour of the unit. This may improve stability with some difficult combinations of source and
load characteristics.
Upon completion of the slew rate setting update, press the Back soft-key to return to the
transient menu or the Home key to return to the home screen.

Slow Slew Rate Limitations
There is a lower limit to the slew rate value that can be used, which is determined by the
combination of slew rate, frequency, duty cycle, and the difference between the two levels. If the
requested transition time (which is the difference between the level settings divided by the slew
rate) is longer than the available time (which is the oscillator period multiplied by the smaller duty
factor), then the transition will not complete before the oscillator initiates a return to the other
level. As a result, the intended level setting will never be reached. In this case, Slew is displayed
in the status line as a warning.

Fast Slew Rate Limitations
In practice there are a number of limitations on the fastest slew rate actually attainable. One is
the minimum transition time of the power stages of the load (which depends on the operating
mode – see the Specification). If a combination of a fast slew rate and a small change in level
imply a transition time shorter than this, then the settling time of the power stage will dominate.
The dynamic behaviour of a source and load combination at high slew rates depends on many
factors, particularly interconnection inductance and the damping factor of feedback loops. In
addition, the response of the power stages of the load is slower when operated at very low or
high currents, or at low voltages. In many circumstances, a lower slew rate setting will be needed
to avoid aberrations.
If an attempt is made to set a slew rate faster than is possible in the circumstances, then
significant overshoots and extended settling times can arise. When configuring fast transitions
approaching the limits of the capabilities of the unit, it is strongly recommended that the current
monitor output be viewed on an oscilloscope to verify the results actually obtained. Particular
care should be taken to avoid a fast transition down to a low current, as this may result in the
power stage entering the cut-off state, which incurs a long recovery time and possibly multiple
current pulses.
In CR (constant resistance) mode, where the current is inversely related to the resistance
transition, it is particularly difficult to predict the maximum useful slew rate setting.
23

Voltage and Current Limits
These limits specify values of source voltage and load current which will cause the load to
automatically disable its input if the actual measured voltage or current exceeds the set limit. This
is not an independent hardware trip, but a simple comparison against the meter measurements.
To access the Limits menu, press the Limits soft-key on the home screen. This menu also gives
access to the facility which allows the unit to dissipate up to 600 Watts under intermittent
operation, which is described below.
The V / I soft-key toggles the menu between setting up the two limits, allowing a numeric value
for each to be entered in the usual way. Pressing the None soft-key (or entering a value of zero)
disables that particular limit. Press the Back soft-key or the Home key to return to the home
screen.
While a value is specified for either limit, Lim appears on the status line of the display. Then, if
either of the limits is exceeded a fault message is displayed and the load input is disabled.

Short Term or Intermittent Operation at up to 600 Watts
For situations where the load is only required for short term or intermittent testing of a source, it
is possible for the unit to dissipate up to 600W subject to time and duty cycle limitations.
To enter this mode of operation press the Limits soft-key on the home screen and then press the
600W soft-key. A warning message is displayed outlining the limitations described here. Press
the Confirm soft-key to accept the warning and enter the high dissipation mode. The fan will run
at full speed for as long as this mode is enabled. Press the Back soft-key to return to the home
screen.
In the METERS panel of the home screen, below the calculated power value, the display now
shows a read-out of percentage of the permitted accumulated energy limit. This is calculated
from the product of actual power dissipation and elapsed time and is an indication of the
temperature stress being imposed on the power stage of the load. When this value reaches
100% a warning message is shown on the screen. To avoid unexpected behaviour the load input
is not immediately disabled, however the user must either manually switch off the source or the
load, or at least reduce the dissipation by switching to a lower level setting, otherwise the load will
automatically disable its input ten seconds after the warning is shown. If this trip is allowed to
occur then the input cannot be re-enabled for 60 seconds.
Once the high power condition is removed (or set to a low level) the percentage of limit count will
decrease, giving the user an indication of when it is safe to return to high power operation.
Provided the fault trip did not occur, it is possible to re-enable the input without waiting for the
value to return fully to zero, but the subsequent period of high power operation will be
correspondingly reduced.
This mode is primarily intended for use in situations where periods of high power operation for up
to about one minute are interspersed with periods at zero power for at least twice as long.
However it is also possible to configure transient operation between a high power condition and a
much lower power condition, subject to limitations on the repetition rate. Whilst in this mode, the
transient oscillator Frequency is limited to 1Hz or less, and the Slew Rate is limited to 0·1% of the
maximum available in normal operation. Within these restrictions the load can be set up as
required; if the average power is less than 200 Watts then the thermal duty cycle limitation is
satisfied and the configuration can be used continuously.
Important: it should be recognised that significantly exceeding the recommended duty cycle can
raise the junction temperatures of the power FETs beyond their rating and possibly reduce their
lifetime. Also, repeated rapid changes in dissipation can result in stress fatigue of both the bond
wires and the junction to mounting base interface, so avoid using external voltage control to
implement large dissipation changes at high frequencies. Successful use of this 600 Watt
capability requires the user to exercise a reasonable degree of caution.
To return to normal operation, access the Limits menu again and press the 400W soft-key.
24

Store and Recall Facilities
The instrument is able to store and recall up to 30 user defined sets of load parameters in
non-volatile memory. Each memory location holds all the parameter settings – load Mode, active
level, Level A value, Level B value, Dropout Voltage level, transient Frequency, Duty and Slew
Rate, the state of Slow start and the state of the 600 Watt option.
Both the store and recall menus display a preview of the parameters that are already stored
within each memory location. If a memory location is empty then (---) is displayed. A memory
location can be selected either by using the ▲ or ▼ soft-keys or the knob to step through the
locations in sequence, or by entering the location number directly using the numeric keypad (with
a leading zero if required). The currently selected memory location number (and user-specified
name) is highlighted on the display, and the location number is also displayed above the table of
previewed parameters (this copy of the location number also updates during numeric entry).
Note: the store and recall menus look almost identical, see the menu name in the top left corner
to distinguish between the two.

Store Menu
To access the Store menu, press the Store soft-key on the home screen. There are three
available options that can be applied to each memory location – store the present settings to the
memory location, delete the contents of the memory location and rename the memory location.
To store the present load configuration and settings to a memory location, select the desired
location and then press either the Confirm soft-key (if the location is presently empty) or the
Replace soft-key to overwrite the existing contents. Once stored, the parameters will be shown in
the preview table. If the location was empty prior to the store operation, then the location will
initially be given a default name of Store_nn, where nn is the location number.
To rename a memory location, press the Rename soft-key which opens the character entry
screen. Select a character using the knob, or alternatively the digits 0 to 9 and the decimal point
can be entered using the numeric keys. To enter the selected character, press the Enter soft-key.
To delete the previously entered character press either the CE soft-key or the CE hard-key.
Use the ◄ and ► soft-keys to select the character position. The maximum number of characters
in a memory location name is limited to 10. Upon completion of the character string entry, press
the Confirm soft-key to accept the changes and return to the store menu where the memory
location name will automatically be updated. Alternatively press the Cancel soft-key to reject any
changes and leave the memory location name unchanged.
To delete the contents of a memory location, select the desired location and press the Delete
soft-key. Delete will then be shown in the top left corner of the display and the soft-keys will list
the options of either Cancel (cancel the deletion) or Confirm (confirm that the location contents
are to be deleted). The contents of the memory location are not erased until the Confirm soft-key
is pressed. Pressing the Cancel soft-key will return to the store menu without deleting the
contents of the memory location. As soon as the deletion is confirmed the load parameters and
location name will be replaced with (---).

Recall Menu
To access the Recall menu, press the Recall soft-key on the home screen. To recall the load
parameters from a memory location, select the desired memory location using the ▲ or ▼ softkeys or the knob, and then press the Confirm soft-key. The instrument will then return directly to
the home screen with all the recalled load parameters updated, but the load input will be disabled
to avoid unexpected results. Alternatively press the Back soft-key or Home key to return to the
home screen without recalling the stored load parameters.
If it is required to recall a set-up which was stored when 600 Watt mode was active, then the unit
must be set into the 600 Watt mode from the Limits menu (including acknowledging the warning
message) before entering the Recall menu.
25

Utilities Menu
Pressing the Utilities soft-key on the home screen gives access to four sub-menus to configure
various instrument settings and preferences. Instruments fitted with Digital Remote Control
interfaces have a fifth sub-menu. The selection can be made using either the ▲ or ▼ soft-keys
or the knob. Press the OK soft-key to initiate the selection and enter the sub-menu, or press the
Back soft-key or the Home key to return to the home screen.

Optional Settings
There are two preferences that can be changed: the state of the input enable at power up and
whether the buzzer is enabled. Each preference has two mutually exclusive options, with the
active selection indicated by a . Select the required option using either the ▲ or ▼ soft-keys or
the knob and press the Confirm soft-key to initiate the selection.

Reset to Factory Defaults
Selecting this sub-menu opens a further sub-menu to determine whether to reset just the present
load configuration and parameters (which is useful if a problem is encountered), or just to clear
the contents of every store and recall memory location, or to reset everything.
Proceed with caution before confirming as this process cannot be undone. Press the Confirm
soft-key to accept the reset and return to the utilities menu. Alternatively, to abandon the reset,
press either the Cancel soft-key to return to the utilities menu or the Home key to return directly
to the home screen.
The default settings (which are also set by the *RST remote command) are:
Load Mode:
Constant Current, 80 Amp range.
Level A & Level B:
Zero for all modes, except maximum resistance for CR mode.
Dropout Voltage:
0V.
Slow Start:
Off.
Transient generator: 1 Hz at 50% duty cycle.
Slew rate:
The Default setting for best calibration of the Level settings.
Protection Limits:
Set to None.

Screen Contrast Adjustment
This sub-menu offers the choice of white-on-black or black-on-white display by using the Invert
soft-key. The screen contrast setting then allows the display to be optimised for viewing angle
and ambient temperature. Use the knob to change the setting, watching the screen preview.
Press Confirm to retain the new settings or Cancel to revert to the previous settings and return
to the Utilities menu, or Home to revert and return directly to the home screen.

Calibration
The calibration menu allows for the existing calibration settings to be adjusted and should only be
carried out by qualified personnel with access to the necessary calibrated test equipment. Entry
to the calibration menu requires a password which is published in the Service Guide, along with
details of the calibration procedure. Please contact your supplier if you require a copy.

Interface Settings
The interface settings menu only appears on the programmable version of the instrument. It
allows the setting of the GPIB address and gives an overview of the LAN connection status and
shows the IP address obtained by the unit once the connection is established.
The GPIB address can be adjusted by using the knob, and can be set to any value between
0 and 30, but must be unique on the bus. The unit does not offer a Listen Only capability. The
address is only changed when the Confirm soft-key is pressed; alternatively the address can be
left at its previous value by pressing the Cancel soft-key.
26

Analogue Remote Control
Two forms of voltage controlled remote operation are available: External Voltage Control, where
an analogue voltage fully defines the demanded level of the chosen operating mode, and
External TTL Control where an external logic voltage selects between the two levels set as
Level A and Level B. The same rear panel control voltage input is used for both of these modes.
The controlling voltage is applied to the two CONTROL VOLTAGE terminals on the rear panel.
Each terminal has an input impedance of nominally 400kΩ to the load negative terminal.
A differential line receiver allows common mode voltages up to ±100 Volts. The common mode
rejection is better than –66dB (50mV at 100V); although it is typically much better than this
(-80dB), the effect on the programmed level can be significant. Consideration should also be
given to the return path for the input currents.
Pressing the Extern soft-key on the home screen opens the external selection menu, where
either the knob or the ▲ and ▼ soft-keys can be used to highlight the desired external control
method. Pressing the Enable soft-key switches to the highlighted method; alternatively pressing
either the Back soft-key or Home key returns the instrument to the home screen leaving the level
select unchanged.
To return from external to internal control, use one of the three LEVEL SELECT keys.

Remote Voltage Control
When External Voltage Control is enabled, the Ext lamp will illuminate and Ext V will be
displayed in the status line. The internal Level A and Level B parameters no longer have any
effect. The load mode and full scale range can still be changed in the usual way if required. The
Dropout Voltage setting remains active, if it is set above zero.
The CONTROL VOLTAGE input has a scaling factor of 4 Volts full-scale. The conversion factors for
each mode and range are:
Operating Range Scale Factor
80 Amps 20 Amps per Volt
8 Amps 2 Amps per Volt
80 Volts 20 Volts per Volt
8 Volts 2 Volts per Volt
400 or 600 Watts 150 Watts per Volt
400 Ohms 100 Ohms per Volt
10 Ohms 2·5 Ohms per Volt
1 A/V (Siemens) 0·25 A/V (Siemens) per Volt
40 A/V (Siemens) 10 A/V (Siemens) per Volt
The slew rate circuit and setting remains in circuit and the required transient wave shape can be
obtained by adjusting these settings in combination with the shape of the signal applied to the
remote input, subject to the transition time limitations of the load circuit.

Remote Level Select
When External TTL Control is enabled, the Ext lamp will illuminate and Ext TTL will be displayed
in the status line. If the external signal applied to the CONTROL VOLTAGE input is below the logic
threshold (nominally + 1·5 V) then the level set by the Level A control is active; if the signal is
above the threshold then the level set by the Level B control applies. Any logic signal (TTL or
other) which crosses the 1·5V threshold is satisfactory. The transitions are defined by the setting
of the slew rate. All parameters can be changed as required in the usual way.
27

Application Notes
This chapter is intended to give helpful information concerning practical applications of the unit.
All electronic loads are subject to the impact of source characteristics, interconnection inductance
and feedback loop characteristics, which can give rise to unexpected instability or poor dynamic
behaviour. The information given here will assist in understanding the factors involved. The initial
sections below cover general considerations, while later sections provide greater detail on the
particular characteristics of each operating mode.

Grounding the Current Monitor Output
A scope will often be used to view the voltage and current waveforms, particularly when using the
transient capabilities of the load to investigate the behaviour of a source. Take care to select a
suitable point to connect the scope ground, as voltage drops on the interconnecting cables
(particularly transients caused by inductance) can give misleading results. The Current Monitor
Output from the load is designed to avoid multiple grounds, as it provides common mode
rejection for differences from the load negative terminal up to a few volts. The negative terminal
of the current monitor must be connected to the load input negative terminal somewhere in the
circuit. If there is already another ground connection, then use that same point, otherwise the
best ground point is usually the negative terminal of the source.
Note that if the load is used with a source having the positive terminal grounded, then any
instrument attached to the Current Monitor negative terminal (and therefore also to the load
circuit negative) must be fully floating, to avoid grounding both terminals of the source.

Sources
Batteries are a low impedance source and, apart from the possibility of inductance in the
interconnecting leads, they are generally easy to use in conjunction with an electronic load. The
dropout facility should be used to protect batteries from being damaged by excessive discharge.
Electronic supplies have active feedback networks whose dynamic characteristics often interact
with the load. When that load (like this instrument) also includes an active feedback controlled
network, whose dynamic characteristics in turn depend on the nature of the source, it will be
apparent that the behaviour of the resulting system can be impossible to predict.

Source resistance
If a source has significant resistance (including the resistance of the connecting leads), so that
the voltage falls as the current rises, it is important to ensure that the voltage across the load
terminals remains at all times above the minimum permissible operating voltage.
The particular considerations concerning source resistance which apply in Constant Power mode
are discussed in the section covering that mode below.

Source inductance
Source and interconnection inductance has a major impact on the behaviour of the load: the
fundamental characteristic of an inductance is that it generates an emf to oppose any change in
current. As the current rises, the emf generated by the inductance reduces the voltage across the
load terminals, perhaps to the point where the load saturates. Whenever the voltage falls below
about 3V the transconductance of the power stage changes considerably; this changes the
damping factor of the feedback loop and alters its dynamic behaviour, possibly giving rise to
overshoots or even oscillation.
Whenever the load current falls, the inductor will generate a voltage transient which might exceed
the voltage rating of the load. The unit is fitted with varistors designed to absorb non-repetitive
transients up to 80 Joules, but repetitive energy up to only 2 watts. Even if the overvoltage
detector disables the load input, these varistors remain connected, so if either of those energy
limits is likely to be exceeded then some form of external protection must be added, such as a
catching diode across the inductor in the source.
28

Shunt capacitance
The load can only sink current, so it can only pull the voltage at its terminals down. The source
must pull the voltage up, including providing charging current to any capacitance across the
terminals. If the total current available is more than sufficient to charge this capacitance at the
slew rate required, then the load will continue to conduct the excess current during the transition
and the behaviour will be as expected. However, if the source cannot charge the capacitor at the
required slew rate, then the load will cut-off until the final voltage is reached. There will then be
an overshoot as it starts to conduct, followed by a ringing as the source responds.

Stability of Source and Load Combinations
This instrument is optimised for accuracy under constant load conditions by using a high gain
feedback loop. Because of this, the possibility exists for combinations of source, interconnection
and load characteristics to give rise to instability. There are three major potential causes:
inductance in the wiring between source and load (or an inductive output impedance of the
source), capacitance in parallel with the connection between source and load (including an output
capacitor within the source) and the characteristics of active feedback circuits within the source.
In Constant Power, Conductance and Resistance modes, the system includes an analogue
multiplier used by the load to derive the current requirement from the instantaneous voltage. This
reduces the bandwidth of the loop and adds additional phase shift. In general, Constant Current
mode is the most likely to be stable, but in some cases instability can be avoided by using a
different mode. The conditions that affect the dynamic behaviour of the load in transient operation
also lead to instability, and some of the suggestions in the sections below may be found helpful.
Constant voltage mode operates in a completely different way, by integrating the voltage error to
create a value for the current demand. This results in a system with extremely high gain and
significant potential for instability.
Many supplies have L-C output filters to reduce noise; these introduce extra phase shift into the
overall source and load combination and can increase the possibility of instability. If there is no
damping across the inductor, a resonant circuit can be formed which allows oscillations to build
up to significant amplitude.

Remedial Actions
The compensation networks of the power stages in the load are changed when the Slew Rate is
set to less than 0.001 times the maximum slew rate for the given load mode and range. For
example if constant current mode is selected and set to its high settings range (up to 80A), the
maximum slew rate setting is 2.5A/us, hence the compensation networks are changed at slew
rates settings below 2.5A/ms. Even if the transient facilities are not being used, this change in
compensation reduces the bandwidth and may make the source and load combination stable.
If instability arises, observe the voltage waveform across the load with a scope: if at any point the
voltage rises above the open circuit emf of the source, then there must be an inductive element
present to form a resonant circuit. Some means must be found to insert damping into this circuit.
One technique is to use a network consisting of a capacitor and a resistor in series (sometimes
called a Zobel network), across the input terminals of the load. Many electronic loads have such
a network built-in; it is omitted from this load to maximise its versatility by offering the lowest
possible input capacitance. It can be added externally: values around 2·2µF and 5Ω are
common, but note that this must be a non-inductive power resistor capable of dissipating a few
watts. A flat film type is best – wire wound resistors are not suitable.

Dynamic Behaviour in Transient Operation
When the transient capabilities of the load are used, the dynamic behaviour of the source and
load combination during the transitions depends on similar considerations to those affecting
stability: series inductance, shunt capacitance and feedback loop characteristics. Proper
operation depends on the load neither saturating nor cutting off at any point in the cycle. The
faster the slew rate sought, the more likely it is that aberrations will occur on the transitions.
29

Because of changes in the transconductance of the FETs, the dynamic behaviour of the power
stages changes at both low and high currents, and also at low voltages when the inter-electrode
capacitance increases considerably. In general, behaviour is optimum in the middle of the current
range (5 to 60 Amps) and at voltages between about 3 volts and (if there is significant source
impedance) about 3 volts below the open circuit voltage of the source.
Attempting to achieve a slew rate beyond the capabilities of a source and load combination can
result in substantial overshoot and ringing. Reducing the slew rate, sometimes by just a small
amount, will often improve the response considerably.

Source Characteristics
The purpose of transient testing is to examine the behaviour of any feedback loops within the
source. If the response of the source is under-damped, then in general the use of an active load
will accentuate the effect. This is particularly true in the modes where the load responds to
changes in voltage. At particular transient frequencies (particularly higher frequencies) the load
may excite resonances in L-C filters or match the natural frequency of a feedback loop. This can
result in considerable reaction from the source, possibly to the extent of causing damage.
Mechanical generators have substantial inductance, mechanical inertia and slow response times.
Transient response testing of such sources should only be attempted at low slew rates.

Start-up transients
There are two different start-up conditions to consider depending on whether the source or the
load is switched on first.
If the source is switched on first and the load enabled afterwards then the start-up may have a
small transient, but this will not generally exceed the magnitude of the Level setting, except at
very low current settings (below a few Amps). This transient can be controlled by selecting Slow
Start and setting a gentle Slew Rate.
In the other case, when the load is enabled before the source is switched on, much larger
transients can be generated. The reason for this is that as soon as the load is enabled the
internal feedback loop will attempt to conduct the current demanded by the level setting. In the
absence of a source voltage this will result in the gate drivers applying maximum bias voltage to
the power FETs, reducing their resistance to minimum (<25mΩ) in an attempt to force a current
to flow. This is the condition that produces the Low Voltage warning on the status line of the
display. When the source is switched on and starts to produce a voltage it will initially see this
25mΩ load, which will cause a significant current transient until the feedback loop has time to
respond and reduce the bias on the FETs. There are two means to reduce this. One is to use the
Slow Start facility with a non-zero setting of the Dropout Voltage to ensure that the load does not
attempt to conduct until the source voltage is present, and then set the Slew Rate to control the
initial transient. The second is to use Constant Resistance (CR) mode, when zero source voltage
should cause zero current to flow. Because of the tolerance on internal offset voltages it may be
necessary to set the Dropout Voltage to a small value (a few tens of mV) to ensure that the unit
does not enter the Low Voltage saturation condition (the yellow lamp also indicates this).
If it is desired to test the start-up behaviour of a power supply, the best approach is to use a small
auxiliary supply to pre-bias the load into conduction, together with series isolating diodes to
cause the load current to transfer from this bias supply to the supply under test when it starts to
produce its output voltage.

Characteristics of each Operating Mode
The following sections give a brief description of the way each mode is implemented, and give
some guidance of the effect that has on the application of the load.
The unit has two power stages (each a large FET) in parallel. Local current feedback around
each stage ensures equal power sharing, with overall current feedback to an earlier stage used
to enhance accuracy. This architecture provides fundamentally a constant current sink. Ideally
the operation of the power stages would be independent of the applied voltage, but in practice,
30

both the gain and the inter-electrode capacitance of the FETs vary with operating point,
particularly at low voltages (below about 3V) and at either low or high currents. This results in
slower response and different stability conditions and dynamic behaviour in these regions,
whatever the operating mode.
The other operating modes first derive the current required according to the instantaneous
source voltage applied and then use the power stages to conduct that current.

Constant Current Mode
As described above, this is the fundamental operating mode of the power stages of this
instrument, so it has the simplest feedback loop and the widest bandwidth. The sensed voltage
signal is only used for the meters and protection. Constant current mode is normally used in
conjunction with low impedance power supplies, and will be quite stable unless there is significant
inductance in either the interconnections or the source. Because of the wider bandwidth it is
particularly critical to have low inductance connections in this mode.
Note that the load cannot be used in constant current mode to test a constant current power
supply, as this combination has only two stable conditions: if the load setting is below the supply
limit then the supply will not be in constant current operation and will deliver its maximum output
voltage, whereas if the load setting is above the limit of the supply then the load will saturate at
its minimum operating resistance with the supply delivering its designed current. The best way to
test a constant current supply is to use the load in constant resistance mode, with a suitable
setting of the Dropout Voltage offset, as described below.

Constant Power Mode
Constant Power mode is implemented by using an analogue divider to divide the specified power
setting by the actual sensed voltage to calculate the necessary current. The power stages then
adjust their conductivity in order to obtain this current. If the source voltage falls then the load will
seek to keep the same power level by reducing its resistance to raise the current. The fact that
the current rises as the voltage falls means that the load is acting as a negative resistance. This
behaviour is also exhibited by most switch-mode power supply circuits.
This characteristic raises the possibility of a latch-up condition if the source has a significant
output impedance. To explain this, consider the possibility that the source voltage falls slightly
(perhaps because of noise) – the load responds by increasing the current to maintain the power
level. This causes a further reduction in the terminal voltage of the source (because of its internal
impedance), so the increase in power is less than expected. The load responds to this by
reducing its resistance even more, in an attempt to increase the current and obtain the required
power. A cross-over point is reached when the fall in voltage outweighs the increase in current
and the load cannot draw the required power. This leads to the latch-up condition, with the load at
its minimum resistance (nearly a short-circuit), the voltage across it almost zero, and the source
is delivering its maximum current into the almost short-circuit load. The status line of the display
will be showing the Low Voltage warning.
If the source impedance is purely resistive then this condition will be triggered when the source
terminal voltage falls to half its open circuit voltage (this is the maximum power transfer condition
of classical electrical theory). More commonly, it will also be triggered immediately if the source
reaches a current limit, or enters constant current operation.
The only way to recover from this situation is to disable either the load input or the source output.
The vast majority of electronic sources will start in a current and power limited state at power-up,
so, to avoid immediately entering the latch-up condition, it is necessary to use the slow start
facilities of the load to constrain the power demand while the source builds up its output voltage.
As Constant Power mode has the characteristics of a negative resistance, the possibility always
exists of forming a negative resistance oscillator in combination with the output impedance of the
source. In practice, constant power mode normally operates well in conjunction with sources
designed to supply such a load.

In transient operation, if the source is constant voltage (with low source impedance), then the
current will follow the changes in power demand and the response will be very similar to constant
current mode. If the source voltage falls as the power demand increases, then (as described
above) the current has to increase more than proportionally and the current slew rate rises; this
will limit the maximum useful power slew rate.

Constant Conductance and Resistance Modes
In both these modes, the analogue multiplier-divider is used to derive the current required from
the sensed voltage. In Conductance mode the current required is calculated by multiplying the
sensed voltage by the specified conductance; in Resistance mode the current required is
calculated by dividing the difference between the sensed voltage and the dropout voltage setting
by the specified resistance.
In both cases, the current rises as the applied voltage rises. At equivalent resistance and
conductance settings, the path from the voltage sense input through to the power stage is the
same, so the two modes will exhibit similar stability characteristics.
In transient operation, the two modes are very different. In Conductance mode, the current
required linearly follows the changing conductance value and the behaviour is fundamentally
similar to constant current mode. In Resistance mode, the required current is inversely
proportional to the linearly changing resistance value, so the resulting current waveform is very
non-linear, changing rapidly at the low resistance part of the cycle. This rapid change
accentuates the effect of inductance in the interconnecting leads and can easily lead to
bottoming and overshoots. Resistance mode is best used at higher voltages and modest
currents.
Dropout Voltage and Resistance Mode
The use of the Dropout voltage setting as an offset in Constant Resistance mode allows flexibility
in constructing load characteristics for particular circumstances. For example, setting a low value
of resistance and a significant value of dropout voltage yields a characteristic similar to a string of
LEDs or a Zener diode and provides an alternative to Constant Voltage mode (see below) but
without the extreme stability problems of that mode.

Constant Voltage Mode
Constant Voltage mode is more likely to exhibit instability than any other mode, especially when
used in conjunction with electronically regulated sources. It is primarily useful with true wideband
current sources which maintain their high output impedance at all frequencies. It will also operate
satisfactorily with resistive sources of moderate impedance, such as photovoltaic cells.
The behaviour required in Constant Voltage mode is the opposite of the fundamental operation of
the power stages of the load, which are intrinsically a voltage independent current sink, so it is
implemented in an entirely different manner to all other modes. The difference between the
sensed voltage and the required voltage is applied to an integrator with a short time constant.
The output of this integrator (which is, in effect, a guess at the current required) drives the power
stages. The operation of this mode therefore depends entirely on feedback action.
The presence of the integrator means that the low frequency transconductance of the load (the
change in load current caused by a small change in sensed voltage) is very high: many
thousands of Amps per Volt. This combines with the output resistance of the source to produce a
system with extremely high loop gain. High frequency instability can result in the normal way if
the phase shift around the loop reaches the threshold for oscillation before the gain has rolled off
below unity. Generally such oscillations will be roughly sinusoidal, at a frequency of many kHz.
The addition of a series CR (Zobel) network across the load, as discussed above, may eliminate
such instability. Alternatively, series resistance between source and load might be helpful.
A more common instability arises from the transient behaviour of the source. The simplest
visualisation of this is to start with the load suddenly increasing its current (perhaps because the
source voltage has just risen above the set point). This increase in current causes a transient
reduction of the output voltage of the source (depending on its transient response) which causes
the voltage to fall below the setting of the load, which in response ceases to conduct current. This
32

in turn results in a transient increase in the output voltage of the supply, and then the process
repeats. This type of instability can be recognised by the characteristic short pulses of current
separated by longer periods of zero current. Sometimes this instability can be avoided by setting
the load threshold well below the open circuit output voltage of the source. Adding resistance in
the connection between source and load may also be helpful.
Another possible form of oscillation can arise if the source has a large output capacitor; this is
characterised by a sawtooth voltage waveform, and is often called a relaxation oscillation.
The operation of the Slow Start circuit is modified in Constant Voltage mode to implement one
common technique to avoid triggering instability. When the load is initially enabled with Slow Start
active, its effective voltage setting starts at 80V (which should be above the open circuit voltage
of the attached source) so no current flows. The slow start circuit progressively reduces the
voltage setting (as determined by the configured Slew Rate). No current flows until the setting
falls past the output voltage of the source. Depending on the output resistance of the source the
current will then gradually increase until the source has been pulled down to the final voltage
setting and the slow start circuit no longer has any effect, leaving stable operation at the desired
operating point.
If Constant Voltage mode cannot be made stable, it is possible to use the offsetting capability of
Constant Resistance mode as described above. The Dropout voltage level is set to just below the
required voltage and the resistance level setting is used to define the slope resistance. Even
quite small values of resistance setting will reduce the gain far below that of voltage mode and
allow stable operation to be obtained.

Multiple Unit Operation
It is possible to operate two loads in parallel in Constant Current mode, which will double both the
current handling and power dissipation capability of a single unit. The connections to the source
should be matched as well as possible.
Note that additional stability issues may arise, because of phase response differences between
the units; the use of more than two units in parallel is not recommended. Multiple unit operation
should not be attempted in any operating mode other than Constant Current.

Zero Volt Operation
Although this unit is designed with very low internal resistance (less than 25mΩ) to enable
operation down to low voltages at high currents, there are occasions when a load is needed
capable of conducting the full current down to zero voltage. This can be achieved by connecting
an additional voltage supply in series with the source under test to boost the voltage at the input
to the load. It is strongly recommended that a diode should also be included (in series) in the
circuit, to ensure that reverse current cannot flow.
The additional supply must be capable of providing the full load current and must have a dynamic
performance that does not impair the stability of the combination. If possible, the use of batteries
is recommended, but note that the direction of the current discharges the battery, so care must
be taken to avoid full discharge.
External voltage sensing must be used, with the sense leads connected to the actual source
under test. The additional supply must provide a voltage of at least the minimum operating
voltage of the load (at the current concerned), plus any voltage drop in the inter-connections, but
the maximum voltage permitted by the external sense circuit is 6 Volts.
Note that if the circuit does not include the series diode recommended, then it is possible for the
combination of the additional supply and the load (in a low impedance condition) to apply a
reverse voltage to the source under test. It is strongly recommended that a switch, capable of
disconnecting the full load current, should be included in the circuit.
The load has a diode across the input terminals that will conduct current if reverse
polarity is applied to the load, even if the load input is disabled.

Remote Interface Configuration
The LD400P model can be remotely controlled via its RS232, USB, GPIB or LAN interfaces.
The GPIB interface provides full facilities as described in IEEE Std. 488 parts 1 and 2.
The RS232 interface communicates directly with a standard COM port.
The USB interface enumerates as a Communications Class device and interacts with application
software through a standard virtual COM port device driver on the PC. The instrument firmware
can be updated in the field via the USB port; see the ‘Maintenance’ chapter for details.
The LAN interface is designed to meet LXI (Lan eXtensions for Instrumentation) version
1.4 LXI Core 2011. Remote control using the LAN interface is possible using the TCP/IP Sockets
protocol. The instrument also contains a basic Web server which provides information on the
unit and allows it to be configured from a web browser. Simple command line control from the
browser is also possible.

GPIB Interface
The standard GPIB interface 24-way connector is located on the instrument rear panel. The pin
connections are as specified in IEEE Std. 488.1-1987 and the instrument complies with both
IEEE Std. 488.1-1987 and IEEE Std. 488.2-1987.
It provides full talker, listener, service request, serial poll and parallel poll capabilities. There are
no device trigger or controller capabilities. The IEEE Std.488.1 interface subsets provided are:
SH1, AH1, T6, L4, SR1, RL2, PP1, DC1, DT0, C0, E2.
The GPIB address of the unit is set from the front panel: from the Home screen select the
Utilities menu then Interface Settings. The present GPIB address is displayed. If it needs to be
changed, use the rotary knob to set the desired address and then press the Confirm soft-key.
The interface will operate with any commercial GPIB interface card, using the device drivers and
support software provided by the manufacturer of that card.

RS232 Interface
The 9-way D-type serial interface connector is located on the instrument rear panel. It should be
connected to a standard PC port preferably using a fully wired 9-way 1:1 male-female cable
without any cross-over connections. Alternatively, a 3-way cable can be used, connecting only
pins 2, 3 and 5 to the PC, but with links made in the connector at the PC end between pins 1, 4
and 6 and between pins 7 and 8, as shown in the diagram:

Most commercial cables provide these connections.
In addition to the transmit and receive data lines, the instrument passively asserts pins 1 (DCD)
and 6 (DSR), actively drives pin 8 (CTS) and monitors pin 4 (DTR) from the PC. This allows the
use of a fully wired 9-way cable.
The Baud Rate for this instrument is fixed at 9600; the other parameters are 8 data bits, no parity
and one stop bit. Flow control uses the XON/XOFF protocol, but because of the low volume of
data associated with this instrument it is very unlikely that flow control will actually be invoked.
34

USB Interface and Device Driver Installation
The instrument firmware can be updated in the field through the USB port. This does not need
the driver described here. It requires a PC software utility provided by the manufacturer, and uses
a HID driver that will already be installed on the PC. If that is the only USB functionality required,
download the package containing the firmware update together with the PC utility from the
manufacturer, and follow the instructions included.
Using the USB interface for remote control requires a Communications Device Class driver on
the PC to provide a virtual COM port instance. In Windows a suitable driver is provided by
Microsoft, but it is not installed by default. The data (.INF) file to control the installation is provided
on the Product Documentation CD delivered with the unit; however the same driver is also used
by many other instruments from this manufacturer and may already be known to the PC.
To install the driver for the first time, first switch the unit on, and then connect the USB port to the
PC. The Windows plug and play functions should automatically recognise the attachment of new
hardware to the USB interface and (possibly after searching the internet for some time) prompt
for the location of a suitable driver. Follow the Windows prompts and point to the CD, then the
sub-directory for this product, and then to the USB Driver sub-directory below that. The file is
named USB_ARM_VCP_xxx.INF, where xxx is a version number. (A readme.pdf file will also be
found in that directory if further assistance is needed.)
In some cases Windows will not complete this procedure (especially recent versions which
search the internet first, looking for the unique Vendor ID and Product ID), in which case the
instrument will show in Device Manager as “not working properly”. If this happens, select this
device, right click and choose “update driver software...” and then “browse this computer for
driver software...” and then locate the .INF file on the CD as described above.
Once Windows has installed the device driver it will assign a COM port number to this particular
unit. This number will depend on previous COM port assignments on this PC, and it may be
necessary to use Device Manager to discover it. Each instrument has a unique USB identifier
which is remembered by the system, so it will receive the same COM port number whenever it is
attached to the same PC (regardless of the physical interface socket used), even though the
COM port will disappear while the instrument is disconnected or switched off. Other instruments
will receive different COM port numbers.
Note that a different PC will not necessarily assign the same COM port number to a particular
instrument (it depends on the history of installations), however Device Manager can be used to
change the assignments given.
This virtual COM port can be driven by Windows applications (including a terminal emulator) in
exactly the same way as any standard COM port, except that the Baud rate and other settings
are unnecessary and are ignored. Some old applications might not function with COM port
numbers 3 or 4, or above 9. In this case, use Device Manager to change the allocation given.
Once it is installed, the driver will be maintained by Windows Update in the usual way.

LAN Interface
The LAN interface is designed to comply with the LXI standard version 1.4 LXI Core 2011 and
contains the interfaces and protocols described below. For more information on LXI standards
refer to www.lxistandard.org .
When powered up and attached to a network, the unit will by default attempt to obtain IP address
and netmask settings via DHCP, or, if DHCP times out (after 30 seconds), via Auto-IP. In the
very unlikely event that an Auto-IP address cannot be found a static IP address is assigned; the
default is 192.168.0.100, but this can be changed on the web page. Connecting via a router is
recommended as this is significantly quicker to assign an IP address; connecting directly to a PC
will only begin to assign an Auto-IP address after the 30 second DHCP timeout.
Since it is possible to misconfigure the LAN interface, making it impossible to communicate with
the instrument over LAN, a LAN Configuration Initialise (LCI) mechanism is provided via a push
switch (marked LAN reset) accessible through a small hole in the rear panel. This restores the
35

default configuration with DHCP enabled, so the unit will then follow the sequence described in
the previous paragraph. Note that resetting the LAN interface removes any password protection.
The progress of establishing a LAN connection can be viewed either by inspecting the Interface
Settings menu (from the home screen press Utilities then Interface Settings) or by interpreting
the symbol shown on the status line of the home screen, which has four possible indications:
No LAN
If the unit cannot detect any connection to a LAN, e.g. the cable is unplugged,
then the LAN status indicator is .
Configuring
The unit has detected a LAN connection but is not yet configured, e.g. is waiting
for DHCP. The LAN status indicator is animated, flashing between
and
LAN OK
The LAN connection is now configured and the unit can communicate. The
display becomes
LAN FAULT
The unit has detected a problem with LAN connection, e.g. Its IP address is in
use by another device. Communication is not possible and the display shows

LAN IP Address and Hostname
To communicate with the instrument through the LAN interface, the IP address (which was
allocated during the connection procedure described above) must be known. Once connected
and correctly configured, the IP address of the unit is displayed within the interface settings menu
(press Home, then select the Utilities menu then Interface Settings). Alternatively the address
can be obtained from the DHCP server, or by using the LXI Discovery Tool described below.
mDNS and DNS-SD Support
The instrument supports these multicast name resolution protocols, which allow a meaningful
host name to be assigned to the unit without needing an entry in the database of a central
nameserver. The desired hostname can be entered on the webpage (which will have to be
accessed by IP address the first time); spaces are not allowed. The name then appears in the
.local domain (e.g. myLD400.local), if the accessing device is configured to support the protocol
(which is the case with most modern PCs). The default name is t followed by the serial number.
ICMP Ping Server
The unit contains an ICMP server allowing the instrument to be ‘pinged’ using its IP address as a
basic communication check, or by its host name if name resolution is working.
Web Server and Configuration Password Protection
The unit contains a basic web server. This provides information on the instrument and allows it to
be configured. The Configure and Instrument Control pages can be password protected to deter
unauthorised changes to the remote operation configuration; the default configuration is ‘no
password’. The Configure page itself explains how to set the password. The password can be up
to 15 characters long; note that the User Name should be left blank. The password and
hostname will, however, be reset to the default (no password) if the rear panel LAN reset switch
is used to reset all the LAN parameters to their factory default.
LAN Identify
The instrument's main web page has an 'Identify' function which allows the user to send a
command to the instrument which causes its display to flash until the command is cancelled.
LXI Discovery Tool
This tool can be used to display the IP addresses and other associated information of all
connected devices that comply with the VXI-11 discovery protocol. It is a Windows PC
application, which is provided on the supplied CD-ROM, that can be installed and run on the
controlling PC, with the unit either connected directly to the PC network connector or via a router.
Double clicking on any entry in the list of discovered devices will open the PC's web browser and
display the Home page of that device. For a later version of the tool that supports discovery by
both VXI-11 and mDNS visit www.lxistandard.org . There are also tools for LAN discovery
36

included as part of the National Instruments Measurement and Automation Explorer package and
the Agilent Vee application.
VXI-11 Discovery Protocol
The instrument has very limited support of VXI-11 which is sufficient for the discovery protocol
and no more.
It implements a Sun RPC Port-mapper on TCP port 111 and UDP port 111 as defined in
RFC1183. The calls supported are:
NULL, GET PORT and DUMP.
On TCP port 1024 a very simple VXI-11 protocol is implemented, sufficient only for instrument
discovery. This implements the following calls:
CREATE LINK, DEVICE_WRITE, DEVICE_READ and DESTROY_LINK.
Once a link has been created anything written to the device is ignored and any attempt to read
from the device returns the same identification string as the *IDN? query.
VISA Resource Name
Because of the limited support for VXI-11 (Discovery Protocol only), the instrument must be
referred to by its raw socket information when used with software packages which communicate
using a VISA resource name. For example, an instrument at IP address 192.168.0.100 would
normally have a VISA resource name of "TCPIP0::192.168.0.100::inst0::INSTR" but for this
instrument the name must be modified to read "TCPIP0::192.168.0.100::9221::SOCKET" where
9221 is the TCP port used by this instrument for control and monitoring, see below.
XML Identification Document URL
As required by the LXI standard, the instrument provides an XML identification document that
can be queried via a GET at “http://IPaddress:80/lxi/identification” that conforms to the LXI XSD
Schema (available at http://www.lxistandard.org/InstrumentIdentification/1.0 ) and the W3C XML
Schema Standards ( http://www.w3.org/XML/Schema ). This document describes the instrument.
The hostname can be used instead of the IP address if name resolution is working.
TCP Sockets
The instrument uses 2 sockets on TCP port 9221 for instrument control and monitoring. Text
commands are sent to this port as defined in ‘Remote Commands’ and any replies are returned
via the same port. Any command string must contain one or more complete commands. Multiple
commands may be separated with either semicolons “;” or line feeds. No final terminator is
required, since the TCP frame implies a terminator, but one may be sent if desired.

Interface Locking
All the remote interfaces are live at all times, to remove any need to select the active interface
and to ensure that the LAN interface is always available (as demanded by the LXI standard). To
reduce the risk of the instrument being inadvertently under the control of two interfaces at once a
simple lock and release mechanism is provided in the instruction set. The lock is automatically
released where it is possible to detect disconnection, or when the Local key is pressed. Access
to the interfaces may also be restricted using the web pages.
Any interface may request to have exclusive control of the instrument by sending an “IFLOCK 1”
command. The lock may only be released by sending an “IFLOCK 0” command from the
interface instance that currently has the lock, and may be queried from any interface by sending
an “IFLOCK?” command. The reply to this query will be “-1” if the lock is owned by another
interface instance, “0” if the interface is free and “1” if the lock is owned by the requesting
interface instance. Sending any command from an interface without control privileges that
attempts to change the instrument status will set bit 4 of the Standard Event Status Register and
put 200 into the Execution Error Register to indicate that there are not sufficient privileges for the
required action.
Note: it is also possible to configure the privileges for a particular interface to either ‘read only’ or
‘no access’ from the Web page interface.
37

Status Reporting
The standard status and error reporting model described in IEEE Std. 488.2 was designed for the
GPIB interface and contains some features intended for use with the Service Request and
Parallel Poll hardware capabilities of that interface, and to accommodate its semi-duplex
operation. Although those facilities are of little use with other interfaces, this instrument makes
the full set of capabilities available to all of the interfaces. A separate set of many of the status
and error registers is maintained for each potential interface instance. The GPIB, USB and
RS232 interfaces each provide a single instance, while the LAN interface provides three: one for
the Web page and one each for the two TCP socket interfaces. Having a separate status model
for each interface instance ensures that data does not get lost, as some status query commands
(e.g. ‘*ESR?’) clear the contents of a register after reading the present value.
The full set of error and status registers and the individual bits they contain is shown in the Status
Model Diagram and described in detail below, but in brief the status is maintained using four
primary registers, the Input State Register, the Input Trip Register, the Standard Event Status
Register and the Execution Error register. A summary is reported in the Status Byte Register, as
selected by three masking registers – the Input State Enable Register, the Input Trip Enable
register and the Standard Event Status Enable Register. Two further mask registers, the Service
Request Enable register and the Parallel Poll Response Enable register, control operation of the
GPIB hardware Service Request and Parallel Poll (and the associated ist message) respectively.
It is recommended that, when controlling the unit through any interface other than GPIB, the
controller program should simply read the primary status registers directly.
The instrument specific Input State and Input Trip Registers record events related to the electrical
function of the load and its interaction with the source under test.
The Standard Event Status Register, supported by the Execution Error and Query Error registers,
records events concerned with command parsing and execution, and the flow of commands,
queries and responses across the interface. These are mainly of use during software
development, as a production test procedure should never generate any of these errors.

Input State and Input Trip Registers (ISR & ISE and ITR & ITE).
These two registers report electrical conditions that have arisen during the operation of the load.
By their nature they are common to all interfaces.
The Input Trip Register reports events that have resulted in the unit unexpectedly disabling the
load input.
The Input State Register reports the present state of the power stage of the load in the same way
as the green and yellow lamps on the front panel and the status line of the display.
Each of these registers has a summary bit in the Status Byte Register, with an associated Enable
Register to determine which, if any, bits contribute to that summary. All these registers are bit
fields, where each bit is independent (so more than one may be set simultaneously) and has the
significance detailed below.
Input Trip Register (ITR)
Bit 7
Fault trip: the input has been disabled by one of the hardware fault detectors.
Bits 6-3 Not used, permanently 0.
Bit 2
Over Current protect: the input has been disabled because the current exceeded the
limit specified by the user.
Bit 1
Over Voltage protect: the input has been disabled because the applied voltage
exceeded the limit specified by the user.
Bit 0
Over Power protect: Set in 600W mode if the permitted power and time limit has been
exceeded by more than 10 seconds.
The bits in the Input Trip register are set when the event they report occurs, and then remain set
until read by the ITR? query. After the Response Message is sent any bits reporting conditions
38

that no longer apply will be cleared; any bit reporting a condition that remains true will remain set.
The Input Trip Enable Register provides the mask between the Input Trip Register and the Status
Byte Register. If any bit becomes ‘1’ in both registers, then the INTR bit (bit 1) will be set in the
Status Byte Register. This enable register is set by the ITE command to a value 0 - 255,
and read back by the ITE? query (which will always return the value last set by the controller). On
power-up the ITE register is set to 0 and ITR is cleared (but bits it contains may be set after
initialisation in the unusual case of any of the conditions reported being true).
Input State Register
Bit 7

Bits 6-5
Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Fault condition: One or more of the hardware detectors is reporting a fault condition.
Caused by excess temperature, input voltage, internal to external sense voltage
difference, or fan failure.
Not used, permanently 0.
Duty cycle protect: Set in 600W mode if the permitted power and time limit is
exceeded.
If no action is taken, an Over Power Protect Trip will follow 10 seconds later.
Voltage below Dropout: the load is not conducting current because the source
voltage is below the dropout voltage setting.
Corresponds to the Dropout warning in the display.
Input nonlinearity: the load is not conducting the current expected because the
power limit circuit is restricting it.
Corresponds to the Power Limit warning in the display.
Input saturation: the load cannot conduct the current required because there is
insufficient voltage from the source.
Corresponds to the Low Voltage warning in the display.
Input Disabled: Reports the present state of the input enable setting.

The bits in the Input State Register continually reflect the present state of the condition they
report. The register can be read by the ISR? query, but this does not change the state of the
contents. On power-up it is normally set to 1 (input disabled), unless the power up option on the
Utilities menu has been set to retain the previous state.
The Input Status Enable register provides a mask between the Input Status Register and the
Status Byte Register. If any bit becomes ‘1’ in both registers, then the INST bit (bit 0) will be set in
the Status Byte Register. This enable register is set by the ISE command to a value
0 - 255, and read back by the ISE? query (which will always return the value last set by the
controller). On power-up it is set to 0.

Standard Event Status Registers (ESR and ESE)
The Standard Event Status Register is defined by the IEEE Std. 488.2 GPIB standard. It is a bit
field, where each bit is independent and has the following significance:
Bit 7
Power On. Set when power is first applied to the instrument.
Bits 6, 3 & 1: Not used, permanently 0.
Bit 5
Command Error. Set when a syntax error is detected in a command or parameter.
The parser is reset and parsing continues at the next byte in the input stream.
Bit 4
Execution Error. Set when a non-zero value is written to the Execution Error
register, if a syntactically correct command cannot be executed for any reason.
Bit 2
Query Error. Set when a query error occurs, because the controller has not issued
commands and read response messages in the correct sequence.
Bit 0
Operation Complete. Set in response to the ‘*OPC’ command.
The Standard Event Status Register is read and cleared by the *ESR? query, which returns a
decimal number corresponding to the contents. On power-up it is set to 128, to report the
power-on bit.
39

The Standard Event Status Enable Register provides a mask between the Event Status Register
and the Status Byte Register. If any bit becomes ‘1’ in both registers, then the ESB bit will be set
in the Status Byte Register. This enable register is set by the *ESE command to a value
0 - 255, and read back by the *ESE? query (which will always return the value last set by the
controller). On power-up it is set to 0.

Execution Error Register (EER)
This instrument specific register contains a number representing the last command processing
error encountered over this interface. The error numbers have the following meaning:
0
100
101
102

103
200

No error has occurred since this register was last read.
Enable Error: For some reason the input enable command cannot be executed. The
cause can be determined by reading the Input Trip and State Registers.
Numeric Error: the parameter value sent was outside the permitted range for the
command in the present circumstances.
Interruption Error: the input has been disabled in order to execute a command (e.g.
a mode or range change) which cannot be performed while the input is enabled.
This error can be avoided by turning the input OFF before sending the command.
Recall Error: the store specified in a RECALL command either does not contain valid
data, or is incompatible with the present setting of the 600W mode selection.
Access Denied: an attempt was made to change the instrument’s settings from an
interface which is locked out of write privileges by a lock held by another interface.

The Execution Error Register is read and cleared using the ‘EER?’ command. On power up this
register is set to 0 for all interface instances.
There is no corresponding mask register: if any of these errors occurs, then bit 4 of the Standard
Event Status Register will be set. This bit can be masked from any further consequences by
clearing bit 4 of the Standard Event Status Enable Register.

Status Byte Register (STB) and GPIB Service Request Enable Register (SRE)
These two registers are implemented as required by the IEEE Std. 488.2.
Any bits set in the Status Byte Register which correspond to bits set in the Service Request
Enable Register will cause the RQS/MSS bit to be set in the Status Byte Register, thus
generating a Service Request on the bus.
The Status Byte Register is read either by the *STB? query, which will return MSS in bit 6, or by a
Serial Poll which will return RQS in bit 6. The Service Request Enable register is set by the *SRE
command and read by the *SRE? query.
Bits 7, 3 & 2: Not used, permanently 0.
Bit 6
MSS/RQS. This bit (as defined by IEEE Std. 488.2) contains alternatively the
Master Status Summary message returned in response to the *STB? query, or the
Requesting Service message returned in response to a Serial Poll.
The RQS message is cleared when polled, but the MSS bit remains set for as long
as the condition is true.
Bit 5
ESB. The Event Status Bit. This bit is set if any bits set in the Standard Event Status
Register correspond to bits set in the Standard Event Status Enable Register.
Bit 4
MAV. The Message Available Bit. This will be set when the instrument has a
response message formatted and ready to send to the controller.
The bit will be cleared after the Response Message Terminator has been sent.
Bit 1
INTR. The Input Trip Bit. This bit is set if any bits set in the Input Trip Register
correspond to bits set in the Input Trip Enable Register.
Bit 0
INST. The Input State Bit. This bit is set if any bits set in the Input State Register
correspond to bits set in the Input Status Enable Register.
40

GPIB Parallel Poll (PRE)
Complete Parallel Poll capabilities are offered by this instrument as defined in IEEE Std. 488.1.
The Parallel Poll Enable Register (which is set by the *PRE command and read by the
*PRE? query) specifies which bits in the Status Byte Register are to be used to form the ist local
message. If any bit is ‘1’ in both the STB and the PRE then ist is ‘1’, otherwise it is ‘0’. The state
of the ist message can also be read directly by the *IST? query.
The physical layer protocol of the Parallel Poll (determining which data line is to be driven and its
logic sense) is configured by the PPC and PPE commands and released by the PPU and PPD
commands in the manner defined by the standard. The instrument implements passive pull-up on
the DIO lines during Parallel Poll.

Query Error Register - GPIB IEEE Std. 488.2 Error Handling
These errors are much more likely to occur on the semi-duplex GPIB interface, which requires
the instrument to hold a response until addressed to talk by the controller. All the other interfaces
provide full duplex communication, with buffering in the physical layer which will usually hold a
response from the instrument until the controlling software reads it; there is no equivalent of the
GPIB state ‘addressed to talk’, so the instrument is not aware of the actions of the controller
The IEEE 488.2 UNTERMINATED error arises if the instrument is addressed to talk and has nothing
to say, because the response formatter is inactive and the input queue is empty. This will cause
the Query Error bit to be set in the Standard Event Status Register, a value of 3 to be placed in
the Query Error Register and the parser to be reset.
The IEEE 488.2 DEADLOCK error arises if the response formatter is waiting to send a response
message and the input queue becomes full. This will cause the Query Error bit to be set in the
Standard Event Status Register, a value of 2 to be placed in the Query Error Register and the
response formatter to be reset, discarding the waiting response message. The parser will then
start parsing the next from the input queue.
The IEEE 488.2 INTERRUPTED error arises if the response formatter is waiting to send a response
message and a has been read by the parser, or the input
queue contains more than one END message. This will cause the Query Error bit to be set in the
Standard Event Status Register, a value of 1 to be placed in the Query Error Register and the
response formatter to be reset, discarding the waiting response message. The parser will then
start parsing the next from the input queue.

Power on Settings
The following instrument status values are set at power on:
ISE
Input Status Enable Register
= 0
ITE
Input Trip Enable Register
= 0
EER
Execution Error Register
= 0
ESR
Standard Event Status Register
= 128 (pon bit set)
QER
Query Error Register †
= 0
ESE
Standard Event Status Enable Register †
= 0
STB
Status Byte Register
= 0
SRE
Service Request Enable Register †
= 0
PRE
Parallel Poll Response Enable Register †
= 0
† Registers marked thus are normally only used through the GPIB interface.
The Input State (ISR) and Trip (ITR) Registers will report any conditions which presently apply.
The instrument will be in local state with the keyboard active. The instrument parameters at
power on are the same as at the last switch off, except 600W mode, which will always be
disabled at power on, and possibly the input enable state, which by default is always off at power
on, but may be configured by the user to be the same at power on as at the last switch off.
41

LD400 Status Model
EXECUTION ERROR
NUMBER
EER?
=/ 0

QUERY ERROR
NUMBER

QER?

=/ 0
6

POWER
ON

COMMAND
ERROR

PON

OPERATION
COMPLETE

CME EXE

QYE

OPC

&
6

ITE

SRQ

*STB?

ESB MAV

MSS

OR
7

&
3

OCP OVP

OPP

&
1

OPW DROP

&
0

LIM

SAT

DIS

&
3

ISE

IST

OR
6

&
5

&
4

*PRE

Set

Query

†

ITR?

Input Trip Register

ITE

ITE?

Input Trip Enable Register

ISR?

Input State Register

ISE

ISE?

Input State Enable Register

†

EER?

Execution Error Register

†

QER?

Query Error Register

†

*ESR?

Standard Event Status Register

*ESE

*ESE?

Standard Event Status Enable Register

*STB?

Status Byte Register

*SRE

*SRE?

Status Byte Enable Register

*PRE

*PRE?

Parallel Poll Response Enable Register

† These registers are cleared after being queried, or by the *CLS command.
42

INTR INST

&
4

ISR?

*SRE

INPUT DISABLED
INPUT SATURATED
INPUT LIMITING
V BELOW DROPOUT
600W WARNING

FAULT
OR

FAULT CONDITION

RESPONSE MESSAGE
READY

RSQ

*ESE

&
7

ITR?
OR

TRIP

*ESR?
OR

600W DURATION TRIP
OVER VOLTAGE TRIP
OVER CURRENT TRIP

FAULT TRIP

Remote Commands
Remote and Local Operation
At power-on the instrument will be in the local state, with normal keyboard operation possible. All
remote interfaces are active and listening for a remote command. When any command is
received from any interface the instrument will enter the remote state. In this state the keyboard
is locked out, the display switches to the home screen, with R E M O T E displayed in place of
the soft-key tabs. The instrument may be returned to the local state by pressing the Local key;
however the remote state will be immediately re-entered if the instrument is addressed again or
receives another command from any interface. It is the responsibility of the user to avoid any
conflict if parameters are changed from the front panel while in the Local state.

Remote Command Handling
Each remote control interface has a separate input queue which is filled, under interrupt, in a
manner transparent to all other instrument operations. The RS232 interface implements flow
control by sending XOFF when the queue contains approximately 200 characters, and then XON
when about 100 free spaces become available. All the other interfaces have standard automatic
flow control mechanisms built into their physical layer communication protocol.
Commands are taken from the input queues by the parser as available. Commands and queries
from each queue are executed in order, but the order of execution of commands from different
interfaces is not defined and should not be relied upon. It is strongly recommended that use
should be made of the interface locking facilities described above. The parser will not start a new
command until any previous command or query is complete. Responses are sent to the interface
which issued the query. There is no internal output queue, so on the GPIB interface the response
formatter will wait, indefinitely if necessary, until the complete response message has been read
by the controller, before the parser is allowed to start the next command in the input queue. On
all other interfaces the response message is immediately sent into buffers in the physical layer.

Remote Command Formats
Commands are sent as by the controller, each consisting of zero or more
elements, separated (if there is more than one such element) by
elements, and finally a .
The is the semi-colon character ';' (3BH).
The , which separates or terminates , is
the new line character (0AH), but in the case of the GPIB interface the hardware END message
may also be used, either with the last character of the message or with the new line. In the case
of the LAN interface, commands may not be split across TCP/IP packet boundaries.
A is any of the commands in the remote commands list, which must be
sent in full as specified. A command must be separated from any parameters by
(which is defined as the character codes 00H to 20H inclusive, excluding the new line character
0AH). No is permitted within any command identifier or parameter, but any other
additional is ignored. Note that the Backspace character (07H) is treated as
, so it cannot be used to delete incorrect characters, and will not hide the error.
The high bit of all characters is ignored and all commands are case insensitive. Commands that
require a numeric a parameter accept the free form format; text parameters must be sent
as Character Program Data as specified.
numbers must be in basic units, may have a decimal point and fractional part, and can
include an exponent part if helpful. They are rounded to the precision supported, so (for transient
frequency) the numbers 10000, 10e3 or 9999.99 all result in 10.00kHz.

Command Timing
There are no dependent parameters, coupled parameters, overlapping commands, expression
program data elements or compound command program headers. Note, however, that the
43

MODE command sets standard values for Level A, Level B, Range and the Slew Rate, so these
must be explicitly set afterwards. Alternatively it is possible to use the store and recall facilities of
the instrument to quickly retrieve a complete set-up of an operating mode and its values.
All commands are separate and sequential, and are executed when parsed and immediately
considered complete. To provide useful functionality, the Operation Complete bit (bit 0) in the
Standard Event Status Register is only ever set by the *OPC command. Either the *OPC
command or the *OPC? query can be used for device synchronisation due to the sequential
nature of remote operations.
The actual electrical response to changes in load settings is subject to the present slew rate
setting, but that is considered to be an aspect of normal operation and not part of the command
execution time. If a slow slew rate is in use the V? and I? queries can be used to check progress.

Response Formats
Responses from the instrument to the controller are sent as , which
consist of one followed by a , which
is the carriage return character (0DH) followed by the new line character (0AH) with, in the case of
GPIB only, the END message NL^END. This is shown as in the descriptions below.
Each query produces a specific which is described in the entry for the
query command in the remote commands list below. Most responses consist of a keyword
followed by either text or a number in one of the following formats:

An integer without a decimal point or a unit.
A fixed point number with a fractional part but no exponent part.
A floating point number with both a fractional part and an exponent part.
Character Response Data, consisting of the text characters listed.

When helpful, numbers are followed by a units indication (which depends on the present load
mode) to provide confirmation. The units used are: A, V, W, OHM, SIE & HZ (SIE is conductance
in Siemens, or A/V.) Slew rates are expressed the basic unit (of the active mode) per second,
with an exponent (which is always positive, with E+03 representing kUnits/s or Units/ms, and
E+06 representing MUnits/s or Units/us).

Command List
This section lists all the commands and queries implemented in this instrument. All numeric
parameters are shown as and may be sent as , or as described above.
Command parameters (unlike responses) are not followed by a units indication.

Instrument Function Commands
MODE

Set the load mode to .
Where can be C, P, R, G or V, corresponding to constant current, power,
resistance, conductance or voltage.
The input will be automatically disabled if not previously done.
If the new mode has two ranges, the MODE command sets the high range.
This command also sets both the Level A and Level B settings to 0 for all
modes except CR, when they are both set to 400Ω, and sets the Slew Rate to
the Default value, which gives the best accuracy of the level settings.

MODE?

Returns the load mode selected.
The response is: MODE where can be C, P, R, G or V.

RANGE

Set the Level Range for the present Load Mode, where has the meaning:
0 = High Range, 1 = Low Range. Note that High range is the default setting.

RANGE?

Returns the load level range.
The response is: RANGE where is either 0 or 1
(0=High Range, 1 =Low Range).

600W

Set 600W mode on or off, where has the meaning:
0=Off (400W mode), 1=On (600W mode).

600W?

Returns the setting of the 600W mode.
The response is: 600W where is either 0 or 1, where
0=400W mode or 1=600W mode.

Set Level A to . The units are implied by the present load mode.

Set Level B to . The units are implied by the present load mode.

Return the set Level of Level A.
The response is: A U
where the is followed by a units suffix determined by the load mode.

Return the set Level of Level B.
The response is: B U
where the is followed by a units suffix determined by the load mode.

DROP

Set the Dropout Voltage level to , in Volts.

DROP?

Returns the set Dropout Voltage level.
The response is: DROP V where is in Volts.

SLEW

Set the Slew rate to , in unit/s (units of the present Load Mode) using an
exponent as required.

SLEW?

Returns the set Slew rate.
The response is: SLEW U where is in Unit/s with the Unit
determined by the present load mode and an exponent part as required.

SLOW

Set Slow Start facility on or off, where has the meaning: 0=Off, 1=On.

SLOW?

Returns the setting of the Slow Start facility.
The response is: SLOW where is either 0 (=Off) or 1 (= On)

LVLSEL

Set the Active Level Select to Where can be A, B, T, V or E
corresponding to Level A, Level B, Transient, Ext Voltage and Ext TTL.

LVLSEL?

Returns the Level Select state.
The response is: LVLSEL Where can be A, B, T, V or E
corresponding to Level A, Level B, Transient, Ext Voltage and Ext TTL.

FREQ

Set the Transient Frequency to , in Hz.

FREQ?

Returns the set Transient Frequency.
The response is: FREQ HZ where is in Hz.

DUTY

Set the Transient Duty Cycle (%A) to , in percent (rounded to integer).

DUTY?

Returns the set Transient Duty Cycle (%A).
The response is: DUTY % where is a percentage.

VLIM
VLIM

Set the Voltage Limit to . Either VLIM 0 or alternatively
VLIM NONE disables and removes any voltage limit.

VLIM?

Returns the Voltage limit. The response is:
VLIM V where is in Volts, or
VLIM 0V if no voltage limit is set.

ILIM
ILIM

Set the Current limit to . Either ILIM 0 or alternatively
ILIM NONE disables and removes any current limit.

ILIM?

Returns the Current Limit. The response is either:
ILIM A where is in Amps, or
ILIM 0A if no current limit is set.

INP

Set the input on or off where has the meaning: 0=Off, 1=On.

INP?

Returns the input state.
The response is INP where is either 0 (=Off) or 1 (= On).

Returns the measured source input voltage.
The response is V where is in Volts.

Returns the measured load current
The response is A where is in Amps.

Common Commands
*IDN?

Returns the instrument identification.
The response is in the form , , ,
where is the manufacturer's name, is the instrument type,
is the interface serial number and is the revision level of the
firmware installed.

*RST

Resets the functional parameters of the instrument to the default settings as
listed in the Factory Default Settings section.
Does not affect the contents of the Save and Recall stores.
Does not affect any remote interface settings.

*SAV

Save the present set-up to the store specified by , where is 1-30.

*RCL

Recall a set-up from the store specified by , where is 1-30.
Configure the unit into 600W mode before recalling a store saved in that mode.
Recalling an empty or invalid store is an execution error.

*OPC

Sets the Operation Complete bit (bit 0) in the Standard Event Status Register.
This will happen immediately the command is executed because of the
sequential nature of all operations.

*OPC?

Query Operation Complete status.
The response is always 1 and is available immediately the command is
executed because all commands are sequential.

*WAI

Wait for Operation Complete true.
This command does nothing because all operations are sequential.

*TST?

The Load has no self-test capability and the response is always 0.

*TRG

The Load has no trigger capability. The command is ignored in this instrument.

Status Commands

*CLS

Clear Status. Clears all status indications, including the Status Byte.
Does not clear any Enable Registers.

ISR?

Query the Input State Register. The response is: .
Does not change the value, which continues to reflect the instrument condition.

ISE

Set the Input State Enable Register to

ISE?

Returns the value in the value in the Input State Enable Register.
The response is: .

ITR?

Query the Input Trip Register. The response format is .
Clears any bits that no longer apply.

ITE

Set the Input Trip Enable Register to

ITE?

Returns the value in the value in the Input Status Enable Register.
The response is: .

EER?

Query and clear Execution Error Register. The response format is .

QER?

Query and clear Query Error Register. The response format is .

*STB?

Report the value of the Status Byte. The response is: .
Because there is no output queue, MAV can only be read by a GPIB serial poll,
not by this query, as any previous message must have already been sent.

*SRE

Sets the Service Request Enable Register to

*SRE?

Report the value in the Service Request Enable Register.
The response is .

*PRE

Set the Parallel Poll Enable Register to the value .

*PRE?

Report the value in the Parallel Poll Enable Register.
The response is .

*IST?

Returns the state of the ist local message as defined by IEEE Std. 488.2.
The response is 0 if the local message is false, or 1 if true.

Interface Management Commands
LOCAL

Go to local. Any subsequent command will restore the remote state.

IFLOCK

Set or Clear the lock requiring the instrument to respond only to this interface,
where has the meaning: 0 = clear and 1 = set the lock.
It is an Execution Error (number 200) if the request is denied either because of
conflict with a lock on this or another interface, or the user has disabled this
interface from taking control using the web interface.

IFLOCK?

Query the status of the interface lock.
The response is: where is
= 0 if there is no active lock,
= 1 if this interface instance owns the lock or
= -1 if the lock is unavailable either because it is in use by another interface or
the user has disabled this interface from taking control (via the web interface).

ADDRESS?

Returns the GPIB bus Address. The response is .

IPADDR?

Returns the present IP address of the LAN interface, provided it is connected.
If it is not connected, the response will be the static IP if configured to always
use that static IP, otherwise it will be 0.0.0.0 if waiting for DHCP or Auto-IP.
The response is nnn.nnn.nnn.nnn, where each nnn is 0 to 255.

NETMASK?

Returns the present netmask of the LAN interface, provided it is connected.
The response is nnn.nnn.nnn.nnn, where each nnn is 0 to 255.

NETCONFIG?

Returns the first means by which an IP address will be sought.
The response is where is DHCP, AUTO or STATIC.

The following commands specify the parameters to be used by the LAN interface. Note: a power cycle is
required after these commands are sent before the new settings are used (or returned in response to
the queries listed above). The instrument does not attempt to check the validity of the IP address or
netmask in way other than checking that each part fits in 8 bits. The rear panel LAN reset switch will
override these commands and restore the defaults as described earlier.
NETCONFIG

IPADDR

NETMASK

Specifies the first means by which an IP address will be sought.
must be one of DHCP, AUTO or STATIC.
Sets the potential static IP address of the LAN interface (as on the webpage).
The parameter must be strictly a dotted quad for the IP address, with each
address part an in the range 0 to 255, (e.g. 192.168.1.101).
Sets the netmask to accompany the static IP address of the LAN interface.
The parameter must be strictly a dotted quad for the netmask, with each part
an in the range 0 to 255, (e.g. 255.255.255.0).
47

Maintenance
The Manufacturers or their agents overseas will provide a repair service for any unit developing a
fault. Where owners wish to undertake their own maintenance work, this should only be done by
skilled personnel in conjunction with the Service Guide, which may be obtained directly from the
Manufacturers or their agents overseas.
Cleaning
If the instrument requires cleaning use a cloth that is only lightly dampened with water or a mild
detergent.
WARNING! TO AVOID ELECTRIC SHOCK, OR DAMAGE TO THE INSTRUMENT, NEVER
ALLOW WATER TO GET INSIDE THE CASE.
TO AVOID DAMAGE TO THE CASE NEVER CLEAN WITH SOLVENTS.
Fuses
The only replaceable fuse in the instrument is an internal fuse on the power supply PCB, which is
intended to protect the unit from the accidental connection of 230V mains supply to a unit which
is configured for 115V operation. Before replacing this fuse, first disconnect the instrument from
all voltages, then remove the cover (6 screws) and ensure that the unit is configured correctly, as
described in the ‘Installation’ chapter of this manual. The correct replacement fuse is:
20x5mm 500mA time-lag (T) 250Vac rated HBC (ceramic tube) fuse.
The transformer primaries are protected by non-resetting thermal fuses inside the windings,
which can only be replaced by fitting new transformers. The secondary circuits are protected by
encapsulated fuses soldered to the PSU PCB. See the Service Guide for replacement details.
Calibration
To ensure that the accuracy of the instrument remains within specification the calibration must be
checked (and if necessary adjusted) annually. The procedure is detailed in the Service Guide,
which also lists the calibrated test equipment required.
Firmware Update
The firmware of the instrument can be updated through the USB port using a PC software utility
available from the manufacturer. This uses a HID (human interface device) USB class driver
which will already be installed on any PC with a USB port. Instructions for the update procedure
are provided with the PC utility and the firmware file.

Troubleshooting
If the instrument does not seem to be operating as expected, check the following before
suspecting a fault.
1. Check the position of the EXT – INT remote voltage sense switch on the rear panel.
2. Check that the voltage drop across the interconnecting cables between source and load is
not excessive, especially if remote sensing is being used. The actual voltage at the input
terminals of the load must meet the minimum operating voltage requirement for the current
level expected. Use a DVM to measure the actual voltage at the terminals.
3. If using a mode other than Constant Current (especially Constant Power or Voltage) consult
the ‘Application Notes’ chapter of this manual for guidance, especially concerning start-up
conditions and stability considerations.
4. If the Input trips as soon as it is enabled, this is often an indication of instability.
5. If the Dropout facility is not required, check that the Dropout Voltage is set to zero.
6. Enter the Utilities menu, perform Restore Factory Defaults and re-configure from scratch.
7. Read the whole of this manual carefully, as operation of the load, and its interactions with the
source, can be quite complex.
48

Sécurité
Cet instrument est conforme à la classe de sécurité 1 de la classification CEI et il a été conçu
pour satisfaire aux exigences de la norme EN61010-1 (Exigences de sécurité pour les
équipements électriques de mesure, de contrôle et d'utilisation en laboratoire). Il s'agit d'un
instrument de catégorie II d'installation prévu pour un fonctionnement à partir d’une alimentation
monophasée standard.
Cet instrument a été testé conformément à la norme EN61010-1 et il a été fourni en état de
sécurité d’utilisation. Le présent manuel d'instructions contient des informations et des
avertissements que l'utilisateur doit suivre afin d'assurer une utilisation sans danger et de
conserver l'appareil dans un parfait état de sécurité d’utilisation.
Cet instrument a été conçu pour être utilisé en intérieur, en environnement de pollution de
deuxième degré à des plages de températures allant de 5 à 40 °C, et à des taux d'humidité
compris entre 20 et 80 % (sans condensation). Il peut être soumis de temps à autre à des
températures comprises entre +5 et -10 °C sans dégradation de sa sécurité. Ne pas le faire
fonctionner en présence de condensation.
L’utilisation de cet appareil d’une manière non spécifiée par les présentes instructions risque
d'affecter la protection de sécurité fournie.
L'unité n'a pas de fusible dans le circuit de charge : si la source connectée à la charge est
capable de générer des courants importants en cas de défaillance, les utilisateurs doivent
évaluer les risques engendrés et envisager l'inclusion d'un fusible, d’un disjoncteur ou d’un
interrupteur approprié dans la connexion entre la source et la charge en question.
Ne pas utiliser l'instrument hors des plages de tension d'alimentation nominale recommandées ni
hors de ses tolérances d'environnement.
AVERTISSEMENT ! CET INSTRUMENT DOIT ÊTRE RELIÉ À LA TERRE
Toute interruption du conducteur de terre du secteur à l'intérieur ou à l'extérieur de l'instrument
rendra l'instrument dangereux. Une interruption intentionnelle est interdite. La sécurité de
l'instrument ne doit pas être annulée par l'utilisation de rallonge sans conducteur de protection.
Lorsque l'instrument est relié au secteur, il est possible que les bornes soient sous tension :
l'ouverture des couvercles ou la dépose de pièces (à l'exception des pièces accessibles
manuellement) risque de mettre à découvert des pièces sous tension. L'instrument doit être
débranché de toute source d'alimentation avant d’être ouvert pour un réglage, un remplacement,
des travaux d'entretien ou de réparations quelconque(s).
Éviter dans la mesure du possible d'effectuer des réglages, des travaux de réparations ou
d'entretien lorsque l'instrument ouvert est branché au secteur. Si cela s'avère toutefois
indispensable, seul un technicien compétent connaissant les risques encourus doit effectuer ce
genre de travaux.
S'il est évident que l'instrument est défectueux, qu'il a été soumis à des dommages mécaniques
ou exposé à une humidité excessive ou à une corrosion chimique, la protection de sécurité en
sera affaiblie et l'instrument ne doit pas être utilisé et doit être renvoyé pour vérification et
réparation.
L’instrument contient à la fois des fusibles encapsulés et des fusibles thermiques sans
réenclenchement ; ceux-ci ne peuvent pas être remplacés par l’utilisateur. Le court-circuitage de
ces dispositifs de protection est interdit.
Ne pas mouiller l'instrument lors de son nettoyage.
Les symboles suivants figurent sur l'instrument ainsi que dans le présent manuel :. -

Avertissement
se reporter à la documentation jointe,
une mauvaise utilisation peut endommager l'instrument.
Courant

Netz OFF (aus)

Alimentation

Sicherheit
Dieses Gerät wurde nach der Sicherheitsklasse (Schutzart) I der IEC-Klassifikation und gemäß
den europäischen Vorschriften EN61010−1 (Sicherheitsvorschriften für elektrische Mess-,
Steuer-, Regel- und Laboranlagen) entwickelt. Es handelt sich um ein Gerät der
Installationskategorie II, das für den Betrieb mit einer normalen einphasigen Versorgung
vorgesehen ist.
Das Gerät wurde gemäß den Vorschriften EN61010−1 geprüft und in sicherem Zustand
geliefert. Die vorliegende Anleitung enthält vom Benutzer zu beachtende Informationen und
Warnungen, die den sicheren Betrieb und den sicheren Zustand des Gerätes gewährleisten.
Dieses Gerät ist für den Betrieb in Innenräumen mit Verschmutzungsgrad 2 und für einen
Temperaturbereich von +5 °C bis +40 °C bei 20 − 80 % relativer Feuchtigkeit (nicht
kondensierend) vorgesehen. Gelegentlich kann es Temperaturen zwischen +5°C und −10°C
ausgesetzt werden, ohne dass seine Sicherheit dadurch beeinträchtigt wird. Betreiben Sie das
Gerät jedoch auf keinen Fall, solange Kondensation vorhanden ist.
Ein Einsatz dieses Geräts in einer Weise, die von dieser Anleitung nicht vorgesehen ist, kann
seine Sicherheit beeinträchtigen.
Das Gerät hat keine Sicherung im Lastkreis: Falls die an der Last angeschlossene Quelle im
Fehlerfall erhebliche Ströme erzeugen kann, muss der Benutzer die damit verbundenen Risiken
bewerten und die Verwendung einer entsprechenden Sicherung, eines Leistungsschalters oder
anderen Schalters in der Verbindung zwischen Quelle und Last in Betracht ziehen.
Auf keinen Fall das Gerät außerhalb der angegebenen Nennversorgungsspannungen oder
Umgebungsbedingungen betreiben.
ACHTUNG! DIESES GERÄT MUSS GEERDET WERDEN!
Jegliche Unterbrechung der Netzerde, ob im Innern oder außerhalb des Geräts, macht das Gerät
zur Gefahrenquelle! Eine absichtliche Unterbrechung ist verboten! Die Schutzwirkung darf durch
Verwendung eines Verlängerungskabels ohne Schutzleiter nicht aufgehoben werden.
Ist das Gerät an die elektrische Versorgung angeschlossen, können die Klemmen unter
Spannung stehen, sodass beim Entfernen von Verkleidungs- oder sonstigen Teilen (mit
Ausnahme der Teile, zu denen Zugang mit der Hand möglich ist) höchstwahrscheinlich
spannungsführende Teile bloßgelegt werden. Vor dem Öffnen des Geräts zu Einstellungs-,
Auswechslungs-, Wartungs- oder Reparaturzwecken ist dieses stets von sämtlichen
Spannungsquellen abzuklemmen.
Jegliche Einstellung, Wartung und Reparatur am geöffneten, unter Spannung stehenden Gerät
ist nach Möglichkeit zu vermeiden. Falls unvermeidlich, sollten solche Arbeiten nur von
qualifiziertem Personal ausgeführt werden, das sich der Gefahren bewusst ist.
Ist das Gerät eindeutig fehlerbehaftet bzw. wurde es mechanisch beschädigt, übermäßiger
Feuchtigkeit oder chemischer Korrosion ausgesetzt, so können die Schutzeinrichtungen
beeinträchtigt sein, weshalb das Gerät aus dem Verkehr gezogen und zur Überprüfung und
Reparatur eingesandt werden sollte.
Das Gerät enthält sowohl eingekapselte Sicherungen als auch eine nicht rückstellbare
thermische Sicherung; diese Sicherungen können vom Benutzer nicht ausgetauscht werden. Es
ist verboten, diese Schutzeinrichtungen kurzzuschließen.
Beim Reinigen darauf achten, dass das Gerät nicht nass wird.
Am Gerät werden folgende Symbole verwendet:
Vorsicht! Bitte beachten Sie die beigefügten Unterlagen.
Falsche Bedienung kann Schaden am Gerät verursachen!
Wechselstrom

Netz OFF (aus)

Netz ON (ein)

Sicurezza
Questo strumento appartiene alla Categoria di Sicurezza 1 secondo la classifica IEC ed è stato
progettato in modo da soddisfare i criteri EN61010−1 (requisiti di Sicurezza per Apparecchiature
di misura, controllo e per uso in laboratorio). È uno strumento di Categoria II di installazione e
inteso per funzionamento con un’alimentazione normale monofase.
Questo strumento ha superato le prove previste da EN61010−1 e viene fornito in uno stato di
sicurezza normale. Questo manuale contiene informazioni e avvertenze che devono essere
seguite per assicurare un funzionamento sicuro e mantenere lo strumento in condizioni di
sicurezza.
Questo strumento è stato progettato per uso interno in un ambiente con grado di inquinamento 2,
nell'intervallo di temperatura che va da 5°C a 40°C, con 20%− 80% UR (in assenza di
condensa). Può occasionalmente essere sottoposto a temperature fra +5°C e −10°C senza
comprometterne la sicurezza. Non usare in presenza di condensa.
L’uso dello strumento in maniera non conforme a quanto specificato in queste istruzioni potrebbe
pregiudicare la protezione di cui è dotato.
L'unità non è dotata del fusibile nel circuito di carico: se la sorgente collegata al carico è in
grado di generare notevoli correnti in caso di guasto, gli utenti dovrebbero valutare i rischi e
considerare l'inclusione di un opportuno fusibile, interruttore automatico o interruttore nel
collegamento tra la sorgente e questo carico.
Non usare lo strumento per misurare tensioni al di sopra dei valori nominali o in condizioni
ambientali al di fuori di quelle specificate.
AVVERTENZA! LO STRUMENTO DEVE ESSERE PROVVISTO DI MESSA A TERRA
L’interruzione della messa a terra all’interno o all’esterno dello strumento ne rende pericoloso
l’utilizzo. L’interruzione intenzionale della messa a terra è severamente vietata. L’azione protettiva
della messa a terra non deve essere annullata dall’utilizzo di una prolunga priva di conduttore di
protezione.
Quando lo strumento è collegato all’alimentazione i terminali potrebbero essere sotto tensione ed
è probabile che l’apertura delle coperture o la rimozione di alcune parti (eccetto quelle a portata
di mano) causi l’esposizione di elementi sotto tensione. L’apparecchio deve essere scollegato da
tutte le sorgenti di alimentazione prima di essere aperto per effettuare regolazioni, sostituzioni,
operazioni di manutenzione o riparazioni.
Qualsiasi regolazione, manutenzione o riparazione dello strumento aperto, in tensione, deve
essere evitata e, se inevitabile, deve essere effettuata esclusivamente da personale competente,
consapevole del possibile pericolo.
Quando sia chiaro che lo strumento è difettoso, o che ha subito un danno meccanico, un
eccesso di umidità, o corrosione a mezzo di agenti chimici, la sicurezza potrebbe essere stata
compromessa e lo strumento deve essere ritirato dall’uso e rimandato indietro per le prove e le
riparazioni del caso.
Lo strumento contiene sia fusibili di tipo incapsulato che di tipo termico senza ripristino; questi
non possono essere sostituiti dall’utente. È vietato cortocircuitare questi dispositivi di protezione.
Evitare di bagnare lo strumento quando lo si pulisce.
Sullo strumento e in questo manuale si fa uso dei seguenti simboli.−
Attenzione Vedere i documenti allegati.
L’uso errato può danneggiare lo strumento.
Corrente Alternata
alimentazione OFF (spenta)

alimentazione ON (accesa)
51

Seguridad
El presente instrumento pertenece a la Clase de Seguridad I de la clasificación CEI y ha sido
diseñado para cumplir las prescripciones de la norma EN61010-1 (Requisitos de seguridad de
equipos eléctricos de medida, control y uso en laboratorio). Se trata de un instrumento de la
Categoría de Instalación II que se debe alimentar con una fuente monofásica normal.
Este instrumento se ha sometido a pruebas con arreglo a la norma EN61010-1 y se suministra
en condiciones de funcionamiento seguro. El presente manual de instrucciones contiene
información y advertencias que el usuario debe seguir, con el fin de garantizar y mantener la
seguridad de funcionamiento.
Este instrumento ha sido diseñado para su uso en interiores, en entornos con una contaminación
de grado 2 y dentro de un intervalo de temperaturas comprendido entre 5 °C y 40 °C, con una
humedad relativa comprendida entre el 20 % y el 80 % (sin condensación). Se puede someter
ocasionalmente a temperaturas comprendidas entre +5 °C y −10 °C, sin que su seguridad se
vea reducida. No se debe utilizar cuando haya condensación.
El uso de este instrumento de forma distinta a la especificada en estas instrucciones puede
afectar a sus mecanismos de seguridad.
La unidad no dispone de fusible en el circuito de carga: si la fuente conectada a la carga es
capaz de generar corrientes significativas en caso de fallo, los usuarios deberán evaluar los
riesgos implícitos y considerar la inclusión de un fusible, disyuntor o interruptor adecuado en la
conexión entre la fuente y esta carga.
No utilice el instrumento con voltajes ni en entornos que se encuentren fuera del intervalo
especificado.
¡ADVERTENCIA! ESTE INSTRUMENTO DEBE CONECTARSE A TIERRA
Cualquier interrupción del conductor de puesta a tierra, dentro o fuera del instrumento, hará que
este resulte peligroso. Está prohibida la interrupción intencionada. No se debe inhibir este
mecanismo de protección mediante un alargador que no tenga conductor de toma de tierra.
Cuando el instrumento esté conectado a la fuente de alimentación puede haber terminales con
tensión y es probable que, si se abre la carcasa o se retiran piezas a las que no sea posible
acceder manualmente en condiciones normales, queden al descubierto componentes con
tensión. Es necesario desconectar el instrumento de cualquier fuente de alimentación antes de
abrirlo para realizar tareas de ajuste, sustitución, mantenimiento o reparación.
Se debe evitar en la medida de lo posible la realización de cualquier tarea de ajuste,
mantenimiento o reparación del instrumento abierto con tensión y, si fuera inevitable, solo la
realizará una persona con la preparación suficiente y que conozca los peligros inherentes.
Si el instrumento resultara estar claramente defectuoso, hubiera sido sometido a un daño
mecánico, a humedad excesiva o a corrosión química, su protección de seguridad podría fallar,
por lo que será necesario dejar de utilizar el aparato y devolverlo para su comprobación y
reparación.
Este instrumento contiene tanto fusibles encapsulados como fusibles térmicos no reiniciables,
los cuales no podrán ser sustituidos por el usuario. Queda prohibido cortocircuitar estos
dispositivos de protección.
No humedezca el instrumento al limpiarlo.
En el instrumento y en este manual se utilizan los siguientes símbolos:
Precaución consulte la documentación adjunta,
una operación incorrecta podría dañar el instrumento.
Corriente alterna (CA).
alimentación de red OFF (desconectada).

l
52

alimentación de red ON (conectada).

Book Part No. 48511-1730 Issue 2

Source Exif Data:

File Type                       : PDF
File Type Extension             : pdf
MIME Type                       : application/pdf
PDF Version                     : 1.6
Linearized                      : Yes
Create Date                     : 2015:11:17 16:44:43Z
Creator                         : Adobe Acrobat 10.0.0
Modify Date                     : 2015:11:17 16:44:43Z
Title                           : 
Has XFA                         : No
XMP Toolkit                     : Adobe XMP Core 5.2-c001 63.139439, 2010/09/27-13:37:26
Metadata Date                   : 2015:11:17 16:44:43Z
Creator Tool                    : Adobe Acrobat 10.0.0
Format                          : application/pdf
Document ID                     : uuid:07246b6b-1a30-410b-8797-7824c7817bfd
Instance ID                     : uuid:695d51a2-b26e-4c6d-b7f6-93ac40c0fd9f
Producer                        : Adobe Acrobat 10.0.0
Page Count                      : 54

EXIF Metadata provided by EXIF.tools

LD400+LD400P Instruction Manual Iss2

Navigation menu

Versions of this User Manual:

Views

Navigation