Fluke 43B Application Note 2066287 Rev A

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Making watt-hour
measurements
with Fluke power
quality analyzers
Introduction
The need to manage power is
never more critical than when
power prices skyrocket and
power quality becomes suspect.
Electrical technicians today are
more aware of power consumption and are on the watch for
consumption that’s higher than
anticipated. Once that occurs,
technicians must become detectives and try to trace the power
consumption back to its source.
Fluke single and three phase
power quality analyzers are
excellent tools for conducting the
portable energy audits necessary
to track down energy draining
devices.
This application note details
the procedures for using Fluke
power quality analyzers for
average watt measurements and
converting those to watt-hours.

Average wattage to
watt-hours conversion
Fluke power quality analyzers
can provide a reading of average
wattage over time, a value that
can be easily used to determine
watt-hours. To convert average
watts to watt-hours, simply multiply the average watts reading
by the amount of time over which
the average was measured.
For example, the following
calculations are for continuous
loads (for cycling loads, see load
cycle considerations):
• A one-watt averaged load
measured for one hour is equal
to one watt-hour; a 1000-watt
averaged load measured for
one hour is equal to one kilowatt-hour.
• A 60-watt averaged load
measured for two hours is
equal to 120 watt-hours.

Application Note

•

A 60-watt averaged load
measured for 15 minutes
(one-quarter hour) is equal to
15 watt-hours.
This technique for measuring
real power consumption (kWh)
can also be applied to apparent
power (kVA) and reactive power
(kVAR). Simply set the power
quality analyzer to calculate the
running average kVA or kVAR,
then multiply by the recording
time to get kVAh or kVARh used
by the load.

Load cycle
considerations
When making average watt
measurements, be sure to take
into consideration the load cycles
you’re working with.
Long cycle loads: If the load
creating the watt draw has a
long on/off cycle, like a refrigerator, be sure to measure long
enough to include several on/off
cycles to get a good representation of the average watts. If possible, try to stop the
measurement at an even number
of on/off cycles to reduce measurement errors.
Short cycle loads: If loads
can cycle on and off or make
large changes faster than one
per minute, use an advanced
three phase analyzer to ensure
the wattage valves are captured.

Using the Fluke 43B Power Quality Analyzer for average
watt measurements.

Making average watt
measurements with the
Fluke 430 Series
On the three phase 430 power
quality analyzers, the energy
function automatically measures
and calculates Watts/VA/VARs.
Simply connect the clamps and
leads and select energy from the
menu.

From the Fluke Digital Library @ www.fluke.com/library

Fluke 43B recording mode with record time
selections from four min to endless (16 days).

Using the Fluke 43B
for average watt
measurements
1. Connect the 43B.
2. Connect the voltage leads
and current clamp before
starting the record mode.
3. Select the power mode and
make sure the wattage readings are correct.

4. Press the record button and
select watts for reading #1.
Reading #2 is not required,
so you may select any of the
other items — VA (volt
amperes) would be a good
choice for reading #2 unless
you have some other need.
5. Selecting record time:
• If you do not know how
long you are going to be
making the watt average
measurements, then use
endless which has a 16-day
maximum. Be sure to keep
an accurate record of how
long the measurement was
made; longer is better to
keep timing errors to a
minimum.
• If you know how long you
want to measure, then
select one of the preset
times (four minutes to eight
days). Use that time value to
calculate the watt-hours
unless you stop 43B record
mode before it stops itself.
In that case, record the
measurement time at which
you stopped the recording.

6. Start the recording.
7. Press the hold button to stop
recording unless you are going
to let it automatically stop on
one of its preset values.
8. Before turning off the 43B or
disconnecting the voltage
leads and the current clamp,
write down the average watt
values or save the screen
information in one of the save
memories.
9. Convert watts to watt-hours as
described on page 1.

Glossary
Apparent Power
(kVA)

In an ac circuit, the power value obtained by multiplying the current by
voltage (P equals IE), with no consideration of the effects of phase angle.

Kilowatt

1,000 watts

Reactance
(X)

The opposition offered to the flow of alternating current by
pure capacitance, inductance, or a combination of the two.

Reactive Power
(kVAR)

The product of kilovolts and amperes in a reactive component of a circuit.

Real Power
(kWh)

The apparent power multiplied by the power factor in an alternating-current circuit
containing reactance. Real power is the difference between the apparent power and
the reactive power. Actual radiated or dissipated power cannot exceed real power.

Watt-hour
(WH)

A unit of electrical energy or work. It is defined as one watt of power sustained for
one hour. A 13-watt lamp operating for 6 hours would consume (13 W) x (6 hrs) = 78 WH.
A larger unit of measurement is the kilowatt-hour (kwh), which is 1000 WH.

For accurate measurement of short cycle loads, use a power recorder with high resolution capabilities.

Fluke. Keeping your world
up and running.
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. (800) 443-5853 or
Fax (425) 446-5116
In Europe/M-East/Africa (31 40) 2 675 200 or
Fax (31 40) 2 675 222
In Canada (800) 36-FLUKE or
Fax (905) 890-6866
From other countries +1 (425) 446-5500 or
Fax +1 (425) 446-5116
Web access: http://www.fluke.com
©2004 Fluke Corporation. All rights reserved.
Printed in U.S.A. 10/2004 2066287 A-US-N Rev B

2 Fluke Corporation

Making watt-hour measurements with Fluke power quality analyzers



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