1 T5_Manual T5 Manual

User Manual: T5_Manual

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Page Count: 48

1 Introduction
2 Sensor description
- 2.1 Design
- 2.2 Analog output signals
3 Installation
4 Service and maintenance
5 Protecting the measuring site
6 Useful notes
7 Troubleshooting
8 Appendix
Your addressee at UMS

Art.Nr. T5

Version 12/2009

Author: tk, ge, ma

User Manual

Pressure Transducer Tensiometer

Introduction

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Table of content

1 Introduction 4

1.1 Safety instructions and warnings 4

1.2 Content of delivery 5

1.3 Foreword 6

1.4 Guarantee 6

1.5 Durability 6

1.6 Tensiometer T5 and T5x 7

1.6.1 Soils and soil water 7

1.6.2 Intended use 7

1.6.3 Typical applications 8

1.6.4 Extended measuring range of the T5x 8

1.6.5 Specific notes 9

1.7 Quick installation guide 10

2 Sensor description 12

2.1 Design 12

2.1.1 Body and shaft 12

2.1.2 Pressure transducer 12

2.1.3 Reference air pressure 12

2.1.4 The ceramic tip 13

2.2 Analog output signals 13

3 Installation 14

3.1 Scientific measure ideas 14

3.1.1 Selecting the measuring site 14

3.1.2 Number of Tensiometers per level 14

3.1.3 Extension of the site 14

3.1.4 Ideal conditions for installation 15

3.1.5 Documentation 15

3.1.6 Selecting the installation angle 15

3.2 Installation procedure 16

3.3 Offset correction for non horizontal installations 17

3.4 Connecting T5 and T5x 18

3.4.1 Spot readings with the INFIELD7 18

3.4.2 Cables 18

3.4.3 General requirements 18

3.4.4 TV-batt Tensiometer power supply 19

3.4.5 Connection to a data logger 19

3.4.6 Tensiometer loggers DL6-te or GP1-te 19

4 Service and maintenance 20

4.1 Refilling 20

4.1.1 When do Tensiometers need to be refilled? 20

4.1.2 Refilling T5 in lab and field 20

4.2 Testing 32

4.2.1 Calibration 32

4.2.2 Check the Offset 32

4.3 Cleaning 33

Introduction

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4.4 Storage 33

5 Protecting the measuring site 33

5.1 Theft and vandalism 33

5.2 Cable protection 33

5.3 Frost 33

6 Useful notes 34

6.1 Extended measuring range 34

6.1.1 The bubble point of the porous cup 34

6.1.2 The vapour pressure of water 34

6.1.3 Boiling retardation: 35

6.2 Maximum measuring range and data interpretation 36

6.3 Temperature influences during measurements 38

6.4 Vapour pressure influence on pF/WC 38

6.5 Osmotic effect 39

7 Troubleshooting 39

8 Appendix 40

8.1 Technical specifications 40

8.2 Wiring configuration 41

8.3 Accessories 42

8.3.1 Connecting and extension cables 42

8.3.2 Handheld measuring device 43

8.3.3 Tensiometer loggers 43

8.3.4 TV-batt power supply 44

8.3.5 T5 auger kit 44

8.3.6 T5-case 44

8.4 Units for soil water and matrix potentials 45

8.5 Index 46

Your addressee at UMS 48

Introduction

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1 Introduction

1.1 Safety instructions and warnings

Electrical installations must comply with the safety and EMC

requirements of the country in which the system is to be used.

Please note that any damages caused by handling errors are out of

our control and therefore are not covered by guarantee.

Tensiometers are instruments for measuring the soil water tension,

soil water pressure and soil temperature and are designed for this

purpose only.

Please pay attention to the following possible causes of risk:

Lightning: Long cables act as antennas and might conduct surge

voltage in case of lightning stroke – this might damage sensors

and instruments.

Frost: Tensiometers are filled with water and therefore are

sensitive to frost! Protect Tensiometers from frost at any time.

Never leave Tensiometers over night inside a cabin or car when

freezing temperatures might occur!

Tensiometers normally are not damaged when the cup is

installed in a frost free soil horizon (in general below 20 cm).

Excess pressure: The maximum non destructive pressure is

300 kPa = 3 bar = 3000 hPa. Higher pressure, which might occur

for example during insertion in wet clayey soils or during refilling

and reassembling, will destroy the pressure sensor!

Electronic installation: Any electrical installations should only be

executed by qualified personnel.

Ceramic cup: Do not touch the cup with your fingers. Grease,

sweat or soap residues will influence the ceramic's hydrophilic

performance.

Do not twist the T5 shaft against the sensor body!

Introduction

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1.2 Content of delivery

The delivery of a T5 or T5x includes:

 Tensiometer, calibrated and filled, with 4-pin plug M12/IP67, with

plug cap

 This manual

 Rubber protection cap, filled with water to the half, for keeping

the ceramic moist and clean

For available accessories see chapter “Accessories”.

The delivery of a T5-set or T5x-set includes:

 Blue plastic transport case

 Tensiometer, filled and calibrated, with 4-pin plug M12/IP67,

plug with protective cap

 This manual

 Rubber protection cap, filled to the half with water to keep

the cup wet and clean

 Pack of paper tissues

 Polyethylene bottle with 250 ml of water

 Filling tube for shafts longer than 10 cm

 Evacuation syringe with acrylic adapter for T5 sensor body

 Evacuation syringe for T5 shaft

 Water reservoir syringe for T5 shaft

 Syringe with pipette tip

 Spare pipette tip

 Gouge auger, diameter 5 mm, length 200 mm

 Sensor body auger, diameter 18 mm, length 200 mm

 Connecting cable; 1,5 m length

Introduction

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1.3 Foreword

Measuring systems must be reliable and durable and should require

a minimum of maintenance to achieve target-oriented results and

keep the servicing low. Moreover, the success of any technical

system is directly depending on a correct operation.

At the beginning of a measuring task or research project the target,

all effective values and the surrounding conditions must be defined.

This leads to the demands for the scientific and technical project

management which describes all quality related processes and

decides on the used methods, the technical and measurement tools,

the verification of the results and the modelling.

The continuously optimized correlation of all segments and it's

quality assurance are finally decisive for the success of a project.

So please do not hesitate to contact us for further support and

information. We wish you good success with your projects.

Yours,

Georg von Unold

1.4 Guarantee

UMS gives a guarantee of 12 months against defects in manufacture

or materials used. The guarantee does not cover damage through

misuse or inexpert servicing or circumstances beyond our control.

The guarantee includes substitution or repair and package but

excludes shipping expenses. Please contact UMS or our

representative before returning equipment. Place of fulfilment is

Munich, Gmunder Str. 37!

1.5 Durability

The nominal lifespan for outdoor usage is 10 years, but protection

against UV-radiation and frost as well as proper and careful usage

extends the lifespan.

Introduction

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1.6 Tensiometer T5 and T5x

1.6.1 Soils and soil water

All water movements in soils are directly depending on the soil water

tension as water - in soils as well as on the surface - always will

move from a point of higher potential to a point of lower potential.

The majority of soil water flows take place at small water tensions.

Only Tensiometers allow the direct and precise measurement of

these small tensions.

Naturally embedded soils are heterogeneous. Not only precipitation

and evaporation effect the processes, but also texture, particle size

distribution, cracks, compaction, roots and cavities. Due to these

heterogeneities the soil water tension varies. Thus, it is reasonable

to have multiple measuring points at least in soil horizons close to

the surface.

1.6.2 Intended use

The intended use of Tensiometers is the measurement of soil water

tension respectively of matrix potential. These Tensiometers work

from +100 kPa (water pressure/level) to -85 kPa (suction/soil water

tension), the T5x even to a lower tension.

If the soil dries out the Tensiometer runs empty and must be refilled

as soon as the soil is sufficiently moist again.

Soil water and Tensiometer water have contact through the ceramic

which is porous and permeable to water. A wetted porous ceramic

creates an ideal pore/water interface. The soil water tension is

directly conducted to the pressure transducer which offers a

continuous signal.

The atmospheric reference pressure is provided through a

membrane on the cable, a distinctive patented method.

The T5 Miniature Tensiometer is specially designed for punctual

measurements, e. g. in soil columns, pots or laboratory lysimeters, or

when the measurement of a minimal span is desired.

With an active surface of only 0,5 cm2 and a diameter of 5 mm the

ceramic tip has all advantages of small dimensions: little soil

disturbance, punctual pick-up and fast response.

Introduction

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1.6.3 Typical applications

Typical applications of the T5 and T5x:

 Punctual measurement of water potential

 Miniature soil column studies, e. g. in combination with micro

water samplers and soil temperature probes

 Determination of pF/wc and K/Psi in soil columns, soil cores

or soil sampling rings

 Determination of leachate and capillary water movements

 Controlling irrigation

 Pot experiments

 Measurements in the upper soil horizons in the field

 Monitoring with data loggers

 Spot readings with the INFIELD7

For in the field applications it might be recommendable to use T4,

T4e or T8 Tensiometers.

1.6.4 Extended measuring range of the T5x

The special version T5x is tested to reach a measuring range of

-160 kPa when delivered. To achieve this, the T5x requires an

absolutely bubble free filling.

You might notice that your T5x might even go down to -250 kPa

before running empty, sometimes even to -450 kPa, but this is an

exception and cannot be guaranteed.

The T5x is identical with the T5 but has a different ceramic. The

extended measuring range is made possible by the effect called

boiling retardation, the special ceramic with smaller pores and, as a

necessary condition, an absolutely gas free filling.

Do not allow the T5x ceramic to dry out by leaving it unprotected

in air: by drying out the tension might reach the destructive

pressure.

Due to the finer pores of the ceramic the water conductivity is

lower. Therefore the response of a T5x is slower than with a

standard T5.

When the shaft is touched it might warm up. This might cause a

short time change of the pressure.

Introduction

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1.6.5 Specific notes

 T5 and T5x are not suitable for dry soils and they are not frost

resistant.

 When installed in the field provide sufficient protection.

 The less air is inside the cup and the better the soil's conductivity

is, the faster the Tensiometer will respond to tension changes.

 It does not make sense to refill a Tensiometer as long as the soil

is dryer than -90 kPa (T5) or - 160 kPa (T5x).

 Using a quartz clay slurry is only recommendable in clayey soils

and only if the drilled diameter is larger than the shaft diameter

(5 mm). In coarse sand or gravel soil a fine grained slurry paste

would act as a water reservoir which would lead to a slower

response.

 The T5 can be installed in any position and orientation. Bubbles

are easily detectable through the transparent shaft.

 Output signals are standardized.

Introduction

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1.7 Quick installation guide

This chapter is only a summary of following chapters. Please read

the complete manual carefully before using the instrument.

T5 are filled and degassed when supplied and are ready for

installation. The procedure is the same for T5 and T5x.

In very soft soils the T5 can be inserted directly without drilling a

hole. As the shaft is fragile, no force should be applied.

For hard soils a special auger kit for is available as an accessory

(art. no. TBT5; included in the T5-set). When the T5 auger is used,

slurrying is unnecessary.

Installation procedure:

1. Drill a hole with the required diameter and depth. Mark the

installation depth on both auger and T5 shaft.

2. Connect the T5 to a readout device, for example a data logger for

continuous measurements or the INFIELD7 handheld device for spot

readings.

During the installation the Tensiometer reading has to be

controlled at any time. Especially in wet, clayey soils a high

pressure might develop while inserting the T5. A pressure of over

3 bar will destroy the pressure transducer. Stop or slow down the

insertion to allow pressure relieve.

3. Carefully remove the water filled rubber cover from the tip and

gently and steadily insert the T5 down to the mark.

Never turn the T5 inside the borehole as this might loosen the

shaft.

Put the protection cup on the plug whenever the plug is not

connected. Dirt will reduce the water tightness of the plug.

Remember to put the protective cap back on the plug after taking

spot readings with the INFIELD7.

Introduction

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Reference air pressure

The reference atmospheric air

pressure is conducted to the

pressure transducer via the air

permeable (white) Teflon

membrane and through the

cable.

Sealed cable

The T5 can be completely buried

if required. If buried cables

should be protected

Sensor body

The incorporated piezoelectric

pressure sensor measures the

soil water tension against

atmospheric pressure.

Acrylic glass shaft

Shafts are available with

lengths from 2 to 20 cm

High grade porous ceramic cup

Filled with degassed water.

Sensor description

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2 Sensor description

2.1 Design

2.1.1 Body and shaft

The sensor body is made of acrylic glass and incorporates the

pressure transducer and all electronic parts. The corpus is backfilled

with resin to hermetically seal the electronics and make the body

watertight.

2.1.2 Pressure transducer

The piezoelectric pressure sensor measures the soil water tension

against the atmospheric pressure. The atmospheric pressure is

conducted through a watertight diaphragm (the white, 2 cm long tube

on the cable) and through the cable to the reference side of the

pressure sensor.

The non destructive maximum pressure is 3 bar (300 kPa).

Higher pressure will damage the sensor and absolutely must be

avoided! High pressures can appear for example when cup and

sensor are reassembled, when inserted in wet, clayey soils or in

tri-axial vessels.

2.1.3 Reference air pressure

The reference atmospheric air pressure is conducted to the pressure

transducer via the air permeable (white) Teflon membrane and

through the cable. The membrane does not absorb water. Water will

not pass through the membrane into the cable, but moisture inside

the cable will leave the cable through the membrane.

The white membrane on the cable must always have contact to air

during a measurement and should never be submersed into water.

Sensor description

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2.1.4 The ceramic tip

To transfer the soil water tension as a negative pressure into the

Tensiometer, a semi-permeable diaphragm is required. This must

have good mechanical stability and water-permeability, but also have

gas impermeability.

The Tensiometer cup consists of porous ceramic Al2O3 sinter

material. The special manufacturing process guarantees

homogeneous porosity with good water conductivity and very high

firmness. Compared to conventional porous ceramic the cup is much

more durable.

The bubble point of a T5 cup is about 200 kPa, of a T5x about 500

kPa. If the soil gets dryer than this air passes through so the

negative pressure inside the cup decreases and the readings go

down to 0 kPa.

With these characteristics this material has outstanding suitability to

work as the semi permeable diaphragm for Tensiometers.

Ceramic cup: Do not touch the cup with your fingers. Grease,

sweat or soap residues will influence the ceramic's hydrophilic

performance.

Do not allow the T5 ceramic to dry out by leaving it unprotected in

air: By drying out the bubble point might be reached, the reading

will go to 0 kPa and air might enter the cup which requires a

refilling.

2.2 Analog output signals

The pressure transducer offers the soil water tension as a linear

output signal, with 1 mV corresponding to 1 kPa.

As the pressure transducer is a Wheatstone full bridge, it has to be

connected in a certain mode. Please read chapter 3.5.3 and the

manual of your display unit or data-logger before connection.

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3 Installation

3.1 Scientific measure ideas

3.1.1 Selecting the measuring site

The installation spot should be representative for the soil which

should be surveyed. For selection it might be necessary to take soil

samples. If the column is refilled care should be taken to achieve the

best possible homogenous distribution and evenly compaction. Bear

in mind a possible shrinking of backfilled columns when T5 are

installed through the cylinder.

On tillage sites (with plants) root spreading and growth during the

measuring period should be considered. Fine roots might develop

around the ceramic cup as it is a poor but assured water source.

Avoid the root zone if possible or replace the Tensiometer from time

to time.

3.1.2 Number of Tensiometers per level

The lower the level the less the variations of water potentials are. In

sandy or pebbly profundities one Tensiometer per depth is sufficient.

Close to the surface about 3 Tensiometers per level are

recommendable.

Guiding principle: More heterogeneous sites and soil structures

require a higher number of Tensiometers.

3.1.3 Extension of the site

Large distance along with high equidistance between the measuring

spots will reduce the influence of sectional heterogeneity.

To determine the water flow according to Darcy two Tensiometers

per horizon or required, one each in an upper and lower level of this

horizon.

Max. recommendable cable lengths for T5 and T5x are 20 meters:

 Accuracy: long cables cause a reduction of the accuracy.

 Lightning: cables act as antennas and should always be as short

as possible.

Installation

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3.1.4 Ideal conditions for installation

For the installation of Tensiometers, the ideal conditions are:

 Frost-free soil.

 Wet coarse clay or loess.

 Low skeletal structure (gravel).

3.1.5 Documentation

For every measuring spot you should:

 measure the installation spot from 2 reference points (A must for

installations below the ground surface).

 Take documenting photos before, during and after installation.

 Save a soil sample.

 Write down installation depth and angle with each sensor

identification (serial number).

 Mark all connecting cables with the corresponding sensor

identification, serial number or logger channel on each end. Clip-

on number rings are available as an accessory.

3.1.6 Selecting the installation angle

An installation position would be ideal if the typical water flow is not

disturbed by the Tensiometer. No preferential water flow along the

shaft should be created.

If the ceramic cup is positioned higher than the sensor body the first

bubble that may appear inside the shaft will block the water

exchange and stop the Tensiometer to measure.

Installation

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3.2 Installation procedure

The following tools are required for installation in the field:

 An auger with diameter 5 mm, preferably the UMS

Tensiometer auger kit TBT5

 Rule, spirit level, angle gauge, marker pen

 Minute book and camera for documentation of site and soil

profile

 Perhaps PE-plastic bags for taking soil samples from the site

1. Drill a hole with the required diameter and depth. Mark the

installation depth on both auger and T5 shaft.

2. If the hole’s diameter is larger than 5 mm mix a paste of water

and grinded soil material.

3. Connect the T5 to a readout device, for example a data logger

for continuous measurements or the INFIELD7 handheld device

for spot readings.

During the installation the Tensiometer reading has to be

controlled at any time. Especially in wet, clayey soils a high

pressure might develop while inserting the T5. A pressure of over

2 bar will destroy the pressure transducer. Stop or slow down the

insertion to allow pressure relieve.

4. If you use a slurry paste pour it into the hole.

5. Pull off the water filled rubber cap from the shaft. Do not turn the

cap as this might unscrew the shaft.

6. Gently and steadily insert the T5 down to the mark while

checking the reading.

Never turn the T5 inside the borehole as this might loosen the

shaft.

The less air is inside the cup and the better the soil's conductivity

is, the faster the Tensiometer will respond to tension changes.

7. Put the protection cup on the plug whenever the plug is not

connected. Dirt will reduce the water tightness of the plug.

Remember to put the protective cap back on the plug after taking

spot readings with the INFIELD7.

Installation

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8. Connect the signal cables as described in the chapter

"Connecting the T5 or T5x".

9. Write down the serial number, position, installation angle and

depth.

10. Protect the cables against rodent bites. Lead the cables through

plastic pipes or use the plastic protection tubes which are

available as an accessory.

3.3 Offset correction for non horizontal installations

The pressure transducer is calibrated without

a cup. Thus, no compensation is required for

horizontal installations.

If a T5 or T5x is installed in a non horizontal

position, the vertical water column draws on

the pressure sensor and causes an offset

shift.

Compensate the offset:

 by calculation,

 by entering the installation angle in the Infield7 for spot readings,

 in the configuration of a data logger by setting an offset.

The deviation is largest for a vertical water column (at 0o). The water

column drawing on the pressure transducer is equal to the shaft

length, ranging from 2 to 20 cm. The offset is shifted for 0,1 kPa per

cm shaft length.

Example: A 5 cm vertical column of water below the pressure

sensor will create an 0.5 kPa offset. This means that when the soil

water tension is 0 kPa the sensor will indicate -0.5 kPa.

(1 cm water column corresponds to a pressure of -0,983 hPa.)

3 mm Centre of

ressure transduce

Centre of ceramic

Installation

3.4 Connecting T5 and T5x

3.4.1 Spot readings with the INFIELD7

T5 and T5x are fitted with a 4-pin plug. The plug can be connected

directly to an INFIELD7 handheld measuring device for taking spot

readings of the soil water tension. The INFIELD7 displays and stores

the soil water tension readings. Stored readings can be downloaded

with the USB converters tL-8/USB or tL-8/USB-Mini which are

available as accessory.

Remember to put the protective cap back on the plug after taking

spot readings with the INFIELD7.

3.4.2 Cables

Connecting and extension cables are required for connecting T5 and

T5x to a data logger or other data acquisition device. Find cables in

the chapter “Accessories”.

Cover plugs with the supplied protective cap if not connected.

3.4.3 General requirements

The pressure transducer is a non-amplified bridge circuit which is

calibrated for 10.6 VDC and requires a stabilized power supply.

Other supply voltages are possible, but the output signal range has

to be recalculated.

In a full-bridge the signal must be measured differentially. This

means do not measure only signal plus against common ground, but

measure the voltage drop between signal minus against common

ground and signal plus against common ground.

The supply voltage has to be constant and stabilized.

The supply voltage must not exceed 18 VDC.

If the Tensiometer is not permanently powered the warm-up

before a measurement should be at least 10 seconds. The 99%

value is reached after 1/100 seconds.

If the Tensiometer is supplied with 10.6 VDC the output signal

range is around 5.3 VDC. A data logger must have the capability

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19/48

to measure such a signal level, but many loggers cannot do this.

In this case use a TV-batt power supply.

3.4.4 TV-batt Tensiometer power supply

The TV-batt power supply is specially designed for Tensiometers T3,

T4, T4e and T5. It offers a stabilized 10,6 V power supply, but with

supply minus = -5 V and supply plus = +5,6 V. Therefore the output

signal will have a logger specific signal level. The Tensiometer

signals are in a range of <1 V.

The TV-batt is directly supplied by battery or 12 V mains power.

3.4.5 Connection to a data logger

Some logger types can measure bridge circuits directly, other

loggers require certain measures as the Tensiometer signal minus

and the supply minus do not have the same ground.

3.4.6 Tensiometer loggers DL6-te or GP1-te

T5 and T5x can be connected directly and without further power

supply to the special Tensiometer loggers DL6-te or GP1-te.

The DL6-te is a stand-alone 6-channel logger with six 4-pin sockets.

All Tensiometer with 4-pin plug are connected to the DL6-te with

extension cables EC-4/...

The GP1-te is a stand-alone 2-channel logger with cable glands. All

Tensiometer with 4-pin plug are connected to the GP1-te with

connection cables CC-4/...

Service and maintenance

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4 Service and maintenance

4.1 Refilling

To assure a rapid and reliable measurement of the soil water

tension, the cup must be filled possibly bubble-free with degassed

water. After dry periods or periods with a large number of wet and

drying out successions, Tensiometers must be refilled.

Refilling is the easiest with the refilling tools included in the T5-set or

T5-case. A readout device, for example the INFIELD7, is always

needed to control the signal.

4.1.1 When do Tensiometers need to be refilled?

Tensiometers need to be refilled:

 the curve of the readings apparently gets flatter (for example a

rain event has no sharp peak but is round),

 the maximum of -85 kPa is not reached anymore.

Refilling is only reasonable if the soil is moister than -90 kPa.

If the soil gets dryer than -85 kPa, the readings will remain constant

at the vapour pressure of water (i. e. for example 92,7 kPa at 20°C

and atmospheric pressure of 95 kPa). By diffusion and slight leakage

the reading will slowly drop within months.

If the soil dries out and reaches the bubble point (-200 kPa for T5;

-500 kPa forT5x), the tension will decrease rapidly as air will enter

the cup.

4.1.2 Refilling T5 in lab and field

This chapter describes the refilling of T5 or T5x using the T5-set.

The procedure has 5 steps:

1. Check the T5 Tensiometer

2. Degas cup and shaft

3. Degas sensor

4. Reassemble

Service and maintenance

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5. Function test

The T5-set includes:

Vacuum syringe with pressure

transducer adapter

Deionised water

Vacuum syringe

for the cup

Filling syringe for the shaft

Drop syringe

Shaft auger &

body auger

Pack of paper tissues

Capillary tube

Service and maintenance

Check the T5

1. First, check if the T5 requires

a refilling: connect it to an

Infield7 or a voltmeter and

power supply.

2. Wrap a dry paper towel

(kitchen roll) around the cup to

dry the ceramic surface.

With short shaft lengths cover

the ceramic with a paper

towel to avoid contamination.

3. Now wave the T5 tip around

in the air. If the reading will rise

to -80 kPa within 10 seconds the

T5 filling is ok.

If this is not the case the T5

needs to be refilled.

4. To disassemble the shaft hold

the sensor body and turn off the

shaft counter-clockwise.

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Service and maintenance

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The pressure sensor diaphragm is inside the small hole on the

pressure sensor body (approx. 2 mm). It is very sensitive and

must never be touched! It can be destroyed even by slightest

contact! No contamination should get on the sealing and gasket.

Degas the cup

If the cup is completely dry just put the shaft in a beaker with

deionised or distilled water over night.

Do not fill any water inside the shaft! If water intrudes from inside

and outside bubbles are trapped inside the ceramic pores. But if

the water only intrudes from the outside and soaks into the inside

any air bubbles are pushed out.

1. Take the syringe with the

short rubber tube.

Pull up 10 ml of deionised or

distilled water.

Take care to avoid bubbles.

2. Remove all air from the

syringe.

Now block the tube with your

finger and pull up the syringe.

This creates vacuum inside the

syringe and dissolved gas is

released. Turn the still

evacuated syringe to collect all

bubbles. Hold the syringe

upright, unblock the tube and

remove all air. Repeat this

procedure until no bubbles

appear anymore.

Service and maintenance

3. Insert the ceramic cup into

the tube as far as possible with

the ceramic pointing inside.

The cup’s tip should be close to

the syringe nozzle.

Pull up the syringe just a little

bit.Hold the syringe down-wards

and tap on it to loosen all

bubbles.

There should be no air inside

the tube around the ceramic. In

case fill in some water with the

syringe.

4. Take off the tube from the

syringe. Leave the shaft inside

the tube.

Remove all air from the syringe

5. Put the tube back on the

syringe.

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Service and maintenance

25/48

6. Now take the vacuum

syringe with the 2 black spacers

and the O-ring on the tube.

Pull up 10 ml water.

7. Degas the water as

described above.

8. Now insert the threaded side

of the T5 shaft completely into

the tube.

Roll up the O-ring so the shaft is

securely fixed: the O-ring should

not be in the range of the thread

but beyond the end of the

thread.

Be careful to keep the parts

clean so there will be no leaking

when vacuum is applied

9. Now pull up the syringe until

both spacers snap in.

Turn the syringe to collect all

bubbles, but do not tap on the

syringe!

Release the spacers and allow

water to flow into the shaft.

Carefully remove the tube from

the syringe nozzle and remove

all air from the syringe (see 6).

Service and maintenance

There should be no air inside the

tube before inserting the shaft

again.

In case fill in some drops of

water into the tube with the

syringe.

Reattach the syringe and pull it

up until the spacers snap in.

Leave the syringes on the shaft.

Degas the sensor body

1. Now take the syringe with the

attached sensor body adapter.

Pull up the syringe, but not

further than shortly before the

spacers will snap in.

2. Hold the syringe upwards

and remove all air.

26/48

Service and maintenance

27/48

3. Insert the sensor body. If you

rotate the sensor it will slip in

easier.

4. Pull up the syringe a few

times. Hold the syringe

downwards so bubbles are

collected inside the syringe.

5. Take off the tube and remove

the air from the syringe.

Leave the sensor inside the

adapter.

6. Squeeze the tube to remove

any air inside while reattaching

the syringe.

Service and maintenance

6. Pull up the syringe until the

spacers snap in.

The Tensiometer water now is

degassing.

Leave both syringe assemblies

for at least 2 hours (the longer

the better).

Reassembling

1. Take of the tubes from the

shaft.

Taking off the syringe from the

sensor body needs care to avoid

damage of the pressure

transducer!

The piston must not snap in

as this might damage the

pressure transducer!

2. Hold the syringe and the

syringe piston securely. Bear in

mind there is still vacuum inside.

Press in the spacers and slowly

release the piston.

28/48

Service and maintenance

29/48

3. Now remove the last

remaining bubbles: draw up the

syringe once more and release

it slowly.

Now take off the syringe and

remove the bubble inside.

3. Reattach the sensor body

and draw up the syringe again.

Tap on the sensor body to

release any bubble.

Let the piston release slowly.

5. Now remove the sensor

body.

6. Add one drop of water onto

the shaft so a bulge of water

overlaps the shaft ...

Service and maintenance

7. … and carefully screw in the

shaft into the senor body.

8. Continuously check the

pressure with the INFIELD7: the

pressure must not exceed 1 bar

You will clearly notice the point

when the shaft hits the o-ring

inside the sensor body.

From this point do only another

quarter turn!

30/48

Service and maintenance

31/48

Check the T5

Zero offset:

Place the T5 flat on the table.

Put a drop of water on the cera-

mic cup.

Now the potential is zero and

the reading should be between

- 3 hPa and + 3 hPa (= -0.3 kPa

to +0.3 kPa).

Check the response:

Open the bottle with the water.

Dry the ceramic surface with a

clean tissue.

Then wave the cup in the air.

The reading should rise to -80

kPa within 10 seconds.

If this is the case, the T5 is filled

perfectly.

To find out the maximum measuring range of this T5 hold the

ceramic tip in the headspace of the bottle over the water.

When you move the ceramic away from the water surface the air

gets dryer and the suction rises.

Hold the ceramic as close to the water surface so the tension

reading will rise slowly. Depending on the filling quality the value will

reach -85 to -450 kPa. Then, the value will rapidly drop to the vapour

pressure (around -90 kPa depending on the altitude). Then,

immediately put some water on the ceramic and cover the ceramic

with the protective bulb which should be filled with water to the half. It

will take one day until the Tensiometer will reach its initial value.

Service and maintenance

32/48

4.2 Testing

4.2.1 Calibration

When delivered Tensiometers are calibrated with an offset of 0 kPa

(when in horizontal position) and a linear response. The offset of the

pressure transducer has a minimal drift over the years. Therefore,

we recommend you check sensors once a year and re-calibrate

them every two years.

Return the Tensiometers to UMS for recalibration, or use the

calibration accessories available from UMS.

4.2.2 Check the Offset

If there is no pressure difference between the cup interior and the

surrounding the signal should be 0 kPa.

There are two ways to check the offset.

1. Connect the Tensiometer to a readout device. Place the T5 in a

beaker and fill the beaker with de-ionized water up to the centre of

the sensor body (see 3.4.) Wait until the reading is stable. If there

are bubbles inside the cup this might take a while.

Now the reading is the approximate offset. The value should be

between +0.3 and -0.3 kPa.

2. To check the zero-point more precisely shaft and sensor body

need to be disassembled.

The pressure sensor diaphragm is inside the small hole on the

pressure sensor body. It is very sensitive and must never be

touched! It can be destroyed even by slightest contact! No

contamination should get on the sealing and gasket.

Before reassembling cup and sensor body carry out the degassing

procedure (see chapter "Refilling").

After taking off the shaft shake the pressure sensor to remove water

from the pressure transducer hole. The offset is acceptable when the

reading is between -0.3 and +0.3 kPa.

Protecting the measuring site

33/48

4.3 Cleaning

Clean ceramic and sensor body only with a moist towel. If the

ceramic is clogged it may be flushed it with Rehalon®.

If the pores are clogged with clay particles saturate the ceramic and

then polish the ceramic surface with a wetted, waterproof sandpaper

(grain size 150...240).

4.4 Storage

If the T5/T5x should not be used for a year or more then empty shaft

and sensor body to avoid algae growth. Store both in a dry place.

5 Protecting the measuring site

5.1 Theft and vandalism

The site should be protected against theft and vandalism as well as

against any farming or field work. Therefore, the site should be

fenced and signposts could give information about the purpose of the

site.

5.2 Cable protection

Outdoors cables should be protected against rodents with plastic

protection tubes. UMS offers dividable protection tubes as

accessory.

In the lab the cables should be fixed so they are not accidentally

pulled away and that there is no risk of stumbling.

5.3 Frost

Tensiometers are filled with water and are endangered by frost. T5

and T5x should only be use in frost-free surroundings.

Do not store filled Tensiometer at temperatures below 0°C. Do not

leave filled Tensiometers over night in your car, in a measuring

hut, etc.

Do not fill the Tensiometers with Ethanol, as this is corrosive for

some materials (i. e. PMMA) and will destroy these.

Useful notes

34/48

6 Useful notes

6.1 Extended measuring range

The extent of the measuring range of a Tensiometer is influenced by

3 factors:

1. The bubble point

2. The vapour pressure (boiling point)

3. The boiling retardation

6.1.1 The bubble point of the porous cup

The bubble point of a porous, hydrophilic structure is specified by the

wetting angle and the pore size. The cups used for UMS

Tensiometers have a bubble point far beyond the measuring range

(8.8 bar). Therefore, the bubble point has no limiting influence.

6.1.2 The vapour pressure of water

At a temperature of 20°C the vapour pressure of water is 2.3 kPa

against vacuum. With an atmospheric pressure of 100 kPa and at

20°C the water will start to boil, or vaporize, as soon as the pressure

drops below 2.3 kPa against vacuum, i. e. 97.7 kPa pressure

difference to an atmospheric pressure of 100 kPa - the Tensiometer

drops out.

The measuring range (at 100 kPa/20°C) is limited to -97.7 kPa.

Atmospheric pressures announced by meteorological services are

always related to sea level. Thus, the true pressure in a height of 500

meters over sea level is for example only 94.2 kPa although 100 kPa

are announced. Then, the measuring range at this height (at 20°C) is

even limited to -91.9 kPa.

If the soil gets drier than the maximum possible measuring range the

reading will remain at this value and then drop gradually towards

zero. If the soil gets as dry as the bubble point a spontaneous

equalisation with the atmospheric pressure occurs. Air enters the cup

and the reading will rapidly go to zero.

Useful notes

35/48

True pressure in heights over sea level at an atmospheric

pressure related to sea level as published by meteorological

services

Height over sea

level (meter) Atmospheric

pressure (kPa) Max. measuring

range at 20°C (kPa)

0 101.3 -99.0

500 95.5 -93.2

1000 89.9 - 87.6

1500 84.6 - 82.3

2000 79.5 -77.2

2500 74.5 -72.2

3000 70.1 -67.8

6.1.3 Boiling retardation:

Water needs a nucleation site to boil. As our Tensiometers have

polished surfaces and a gas-free filling the so called boiling

retardation occurs – the Tensiometer keeps on measuring beyond

the boiling point. To achieve this the T5(x) must have an absolutely

bubble free filling.

Some T5x can go down to -250 kPa before they run dry, occasionally

even a range of -450 kPa is achievable. As this is exceptional there

is no guarantee for this measuring range.

Useful notes

6.2 Maximum measuring range and data

interpretation

The measuring range of Tensiometers is limited by the boiling point

of water. At a temperature of 20°C the boiling point is at 2,3 kPa over

vacuum. So with 20°C and an atmospheric pressure of 95 kPa the

Tensiometer cannot measure a tension below -92,7 kPa, even if the

soils gets drier than that. The readings remain at a constant value

(fig. 7.1, between day 10 and 16).

Interpretation Messwerte bis über 15 bar nahe der

Bodenoberfläche

100

1000

10000

100000

0246810121416182

Zeit

Wasserspannung

Bodenwasserspannung

Tensiometermesswert

Interpretation of readings to -2 bars

Soil water tension

Tensiometer reading

Matrix potential negative (hPa)

Time

Fig. 7.1: Tensiometer readings with tensions to -2 bar

If the soil will get even drier and reaches -2 bar, the ceramic’s bubble

point is reached. The cup water will run out quickly and the reading

of the air filled cup will go to zero (fig. 7.1, day 16-19)

36/48

Useful notes

If there will be rain before the soils reaches -2 bars, the Tensiometer

cup will suck up the soil water. However, the soil water includes

dissolved gas which will degas as soon as a dry soil again will

increase the tension. This will result in a poor response, the signal

curve will get flatter and readings will only slowly adapt to the actual

soil water tension. Depending on the size of the developed bubble

readings will get less close to the maximum (fig. 7.2).

37/48

Interpretation Messwerte unter 2 bar

100

1000

10000

0 5 10 15 20 25 30 35

Matrixpotential negativ

Ze t

Bodenwasserspannung

Tensiometermesswert

Interpretation of readings below -2 bars

Matrix potential negative (hPa)

Soil water tension

Tensiometer reading

Time

Fig. 7.2 Tensiometer readings with tensions below -2 bar

Soil water tensions normally change only slowly. Therefore, a signal

curve with lot of jumps could be an indicator for example for loose

contacts, moisture in defective cables or plugs, poor power supply or

data logger malfunctions.

Useful notes

6.3 Temperature influences during measurements

If the sensor is not powered continuously the voltage should be

switched on 10 seconds before a measurement. In this case, the self

heating is negligible.

The correlation of water tension to water content is temperature

dependent. The influence is low at tensions of 0 to 10 kPa  0 …

0,6 kPa/K, but high for tensions over 100 kPa:































TR ln

 = Water tension R = Gas constant (8,31J/mol K)

M = Molecular weight p = Vapour pressure

po = Saturation vapour pressure at soil temperature

(from Scheffler/Straub, Grigull)

6.4 Vapour pressure influence on pF/WC

If the temperature of a soil with a constant water content rises from

20°C to 25°C the soil water tension is reduced for about 0,85 kPa

due to the increased vapour pressure which antagonizes the water

tension.

Temperature

in °C 4 10 16 20 25 30 50 70

Pressure

change per

Kelvin in [hPa] 0,6 0,9 1,2 1,5 1,9 2,5 7,2 14

38/48

Troubleshooting

39/48

6.5 Osmotic effect

The ceramic has a pore size of r = 0,3 m and therefore cannot block

ions. Thus, an influence of osmosis on the measurements is

negligible because ion concentration differences are equalized

quickly. If the T5 cup is dipped into a saturated NaCl solution the

reading will be 1 kPa for a short moment, then it will drop to 0 kPa

again.

7 Troubleshooting

Please refer to our webpage where you will find a regularly up-dated

list of FAQs:

http://www.ums-muc.de/en/support/faq/tensiometer.html

Appendix

40/48

8 Appendix

8.1 Technical specifications

Material and dimensions

Ceramic material

Bubble point T5

Bubble point T5x

Ceramic cup

Sensor body

Shaft material

Al2O3 sinter

> 200 kPa

> 500 kPa

Length 6 mm,  5 mm

PMMA,  20 mm

Impact-proof PMMA,  20 mm

Sensor cable

Length

Plug 1.5 m

Male 4-pin, thread M12, IP67

Measuring range

T5x

Water tension

Water level

-85 kPa ... +100 kPa

min. -160 kPa ... +100 kPa

-85 kPa (-160 kPa) … 0 kPa (Tensiometer)

0 kPa … +100 kPa (Piezometer)

Output signal

Pressure 160 mV = -160 kPa (T5x)

85 mV = -85 kPa (T5)

0 mV = 0 kPa

-100 mV = 100 kPa (water level)

Accuracy ±0,5 kPa

Power supply

Supply voltage Vin typ. 10,6 VDC by TV-batt (recommended)

5 ... 15 VDC, stabilized

Current consumption 1,3 mA at 10,6 V (TV-batt)

Substance sustainability

pH range pH 3 ... pH 10

Limited to substances that do not harm silicon, flour silicon, EPDM,

PMMA and polyetherimid.

Appendix

41/48

8.2 Wiring configuration

Configuration of T5 and T5x Tensiometer plug and

the 4-wire CC-4 connecting cables:

Signal Wire Pin Function

Vin brown 1 Supply plus

V- blue 3 Supply minus

A-OUT+ white 2 Analog output plus

A-OUT- black 4 Analog output minus

Appendix

42/48

8.3 Accessories

8.3.1 Connecting and extension cables

Cables must be ordered additionally for each Tensiometer.

UMS connecting or extension cables for data logger applications etc.

Connecting cables CC-8/... are fitted with a female plug M12/IP67

and 12 cm wire end sleeves.

Extension cables EC-8/... have one each male and female plug

M12/IP67.

Plugs are supplied with protective caps.

Item Art. no.

4-pin connection cable for T5 and t5x

Length 1,5 m CC-4/1.5

Length 5 m CC-4/5

Length 10 m CC-4/10

Length 20 m CC-4/20

4-pin extension cable for T5 and T5x

Length 5 m EC-4/5

Length 10 m EC-4/10

Length 20 m EC-4/20

Additional items Art. no.

Clip-on cable markers, 30 times numbers 0 ... 9 KMT

Plastic protection tube for cables are available with several diameters, also

dividable slotted tubes for easy re-fitting.

Appendix

43/48

8.3.2 Handheld measuring device

INFIELD7 handheld measuring device for taking and

storing spot readings of soil water tension. Offset

correction of water column and installation angle.

Suitable for all UMS - Tensiometers. The set comes

with refilling tools in small carrying case.

The tL-8/USB-Mini is a USB converter for data

readout of the INFIELD7 via PC or laptop USB port,

incl. Windows PC software tensioVIEW.

Item Art. no.

INFIELD7 set INFIELD7C

USB PC adapter for Infield only tL-8/USB-Mini

8.3.3 Tensiometer loggers

6-channel logger DL6-te for Tensio-

meters T3, T4, T4e, T5 plus 1x counter,

1x temperature, alarm output, 16.000

readings memory, IP68, 4-pin sockets

for extension cables EC-4

Data logger GP1-te with

channels for 2x Tensio-

meters, 2x temperature, 2

counters, 1 relay output,

IP67

Item Art. no.

6-channel logger, incl. software and data cable DL6-te

2-channel logger, incl. software and data cable GP1-te

Appendix

8.3.4 TV-batt power supply

Tensiometer power supply unit for T3, T4, T5, suited in DL2e-logger

extension frame (left), or as an open module (right).

Item Art. no.

TV-batt for DL2e logger TV-Batt/DL2e

TV-batt module only TV-Batt/module

8.3.5 T5 auger kit

Auger kit for T5, with shaft auger, length 250 mm length

and sensor body auger, length 200 mm.

Item Art. no.

T5-auger kit TBT5

8.3.6 T5-case

Service kit for t5 and T5x (without a T5!), incl.

refilling tools (syringes etc.), auger kit,

connecting cable CC-4/1.5, all in blue case 35 x

30 x 8 cm.

Item Art. no.

T5 service kit T5-case

44/48

Appendix

45/48

8.4 Units for soil water and matrix potentials

%rF

99,9993

99,9926

99,9756

99,9261

99,2638

98,8977

92,8772

47,7632

0,0618

psi

-0,1450

-1,4504

-4,9145

-12,345

-14,504

-145,04

-219,52

-1.450,4

-14.504

-145.038

bar

-0,01

-0,1

-0,33

-0,85

-1

-10

-15

-100

-1.000

-10.000

MPa

-0,001

-0,01

-0,033

-0,085

-0,1

-1,0

-1,5

-10

-100

-1.000

kPa = J/kg

-1

-10

-33

-85,1

-100

-1.000

-1.500

-10.000

-100.000

-1.000.000

Cm WS

9,8

98,1

323,6

834,5

980,7

9806,6

14709,9

98.066,5

980.665

9.806.650

hPa

-10

-100

-330

-851

-1.000

-10.000

-15.000

-100.000

-1.000.000

-10.000.000

2,01

2,53

2,93

4,18

FK field

capacity

Standard

Tensiometer

range

Permanent

wilting point

Air dry, air

humidity

dependant

oven dry

Appendix

46/48

8.5 Index

Auger ..................................43

Boiling point ........................35

Bubble point..................13, 35

Cable protection..................34

Calibration...........................33

Ceramic ..............................13

Compensate the offset........17

Connecting cables ..18, 40, 41

Data logger .........................19

Degas the cup.....................23

Degas the sensor body.......27

Destructive pressure.............4

Extension cables.................41

Frost................................4, 34

Gas impermeability.............13

Guarantee.............................6

Installation procedure ...10, 16

Laboratory lysimeters ...........7

Lightning ...............................4

Long cables ..........................4

Maximum pressure .............12

Offset ..................................33

Osmosis..............................38

Output signals.....................13

Plug.....................................40

Porous ceramic...................13

Pots.......................................7

Pressure sensor..................12

Appendix

47/48

Quartz clay............................9

Reassembling.....................29

Reference air pressure .......12

Refilling...............................20

Slurry.....................................9

Soil columns .........................7

Spot readings......................18

T5-set .................................21

Temperature .......................37

TV-batt ..........................19, 43

Typical applications ..............8

Vapour pressure .................37

White membrane ................12

Zero offset...........................31

Your addressee at UMS

48/48

Your addressee at UMS

Sales Georg v. Unold Tel:+49-89-126652-15

Email: gvu@ums-muc.de

About this manual Thomas Keller Tel:+49-89-126652-19

Email: tk@ums-muc.de

UMS GmbH

Ph.: +49-89-126652-0

D-81379 München

Gmunderstr. 37 Fax: +49-89-126652-20

email: info@ums-muc.de

Strictly observe rules for disposal of equipment

containing electronics.

Within the EU: disposal through municipal waste

prohibited - return electronic parts back to UMS.

Rücknahme nach Elektro G

WEEE-Reg.-Nr. DE 69093488

1 T5_Manual T5 Manual

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