UMS T8 User manual

© UMS GmbH München
Art. no. T8
Revision: 12/2011
Authors: an/ge/tk/ma
User Manual
Long-term Monitoring Tensiometer
T
T8 8

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Table of content
1Tensiometer T8 4
1.1 Safety instructions and warnings 4
1.2 Content of delivery 5
1.3 Foreword 5
1.4 Guarantee 6
1.5 Durability 6
1.6 Tensiometer T8 6
1.6.1 Soils and soil water 6
1.6.2 Intended use 6
1.7 Quick start guide 8
2Description of the T8 11
2.1 T8 parts 11
2.1.1 Body and shaft 11
2.1.2 Pressure sensor 11
2.1.3 Reference air pressure 11
2.1.4 Temperature sensor 11
2.1.5 Filling status indicator 12
2.1.6 The ceramic cup 12
2.2 Output signals 13
2.2.1 Analog 13
2.2.2 Digital 13
2.3 Serial interfaces 13
2.3.1 tensioLINK®14
2.3.2 SDI12 14
2.4 Software 15
2.4.1 tensioVIEW 15
2.5 Sensor logging 15
3Installation 16
3.1 Concept planning and installation 16
3.1.1 Selecting the measuring site 16
3.1.2 Number of Tensiometers per level 16
3.1.3 Extension of the site 16
3.1.4 Length and solar protection of refilling tubes 17
3.1.5 Jacket tubes 18
3.1.6 Ideal conditions for installation 18
3.1.7 Documentation 18
3.2 Selecting the installation angle 18
3.2.1 "Vertical" with downwards angle 19
3.2.2 "Horizontal" with upwards angle 19
3.3 Installation procedure 19
3.4 Offset correction for non horizontal installations 22
3.5 Connecting T8 23
3.5.1 Spot reading with the INFIELD7 handheld 23
3.5.2 Connection to a data logger 23
3.5.3 Error caused by single-ended connection 24
3.5.4 Connecting the indicator 24

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4T8 configuration with tensioVIEW®25
4.1 tensioLINK®USB converter 25
4.2 Work with tensioVIEW 25
4.2.1 Menu 25
4.2.2 Current readings 27
4.2.3 Stored readings 27
4.2.4 Configuration of a device 27
4.3 Configuration settings for T8 27
5Service and maintenance 34
5.1 Refilling 34
5.1.1 When do Tensiometers need to be refilled? 34
5.1.2 Refilling in the lab 35
5.1.3 Refilling in the field 36
5.1.4 Refilling with a vacuum pump 38
5.2 Testing 40
5.2.1 Calibration 40
5.2.2 Check the Offset 40
6Protecting the measuring site 41
6.1 Theft and vandalism 41
6.2 Cable protection 41
6.3 Frost 41
6.3.1 Protection against frost 41
6.3.2 Emptying the T8 42
6.4 Lightning protection and grounding 42
7Useful notes 44
7.1 Maximum measuring range and data interpretation 44
7.2 Temperature influences 46
7.3 Vapor pressure influence on pF/WC 46
7.4 Osmotic effect 46
7.5 Using a T8 as a piezometer 47
8Troubleshooting 47
9Appendix 48
9.1 Technical specifications 48
9.2 Wiring configuration 49
9.3 Accessories 51
9.3.1 Connecting and extension cables 51
9.3.2 Handheld measuring device 52
9.3.3 Tensiometer augers 52
9.3.4 Refill kits 53
9.3.5 tensioLINK accessories 53
9.4 Units for soil water and matriy potentials 53
Your addressee at UMS 57

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1 Tensiometer T8
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.

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1.2 Content of delivery
The delivery of a T8 includes:
Tensiometer, calibrated and filled, with 8-pin plug M12/IP67, with
plug cap
This manual
Plastic bottle protecting the ceramic cup (must be filled to half
with water to keep the cup wet)
Rubber shaft water protection disk
Calibration certificate with each order for conversion of electrical
to physical values
Refilling syringe
Foravailableaccessoriesseechapter“Accessories”.
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 modeling.
The continuously optimized correlation of all segments and its quality
assurance are finally decisive for the success of a project.
We wish you good success with your projects. Please do not hesitate
to contact us for further support and information.
Yours,
Georg von Unold

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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 fulfillment 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
substantially extends the lifespan.
1.6 Tensiometer T8
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) to -85 kPa (suction / soil water
tension).
If the soil gets drier than -85 kPa, the Tensiometer runs dry and must
be refilled as soon as the soil is sufficiently moist again (see chapter
5.1).

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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.

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(b)
1.7 Quick start guide
This chapter is only a summary of following chapters. Please read
the complete manual carefully before using the instrument.
In general, the T8 is filled and ready for installation when supplied.
1. Drilling the borehole:
Mark the required drilling depth on auger and on Tensiometer shaft.
Note: drilling depth = Installation depth / cos .
For installation from the soil surface, an installation angle of 25° to
65° from the vertical line is ideal for the optimal removal of air from
the cup (fig. a). For “horizontal” installation from a manhole the
borehole should point upwards in an angel of 5° (fig. b).
2. Slurrying the cup is only recommendable in clayey soils and only if
the bore hole is larger than 24 mm. In coarse sand or pebbly soils
fine pored slurry might create a water reservoir which slows down
the response. With the special Tensiometer gouge auger (article no.
TB-25) slurrying is unnecessary because of the accurate fitting of the
Tensiometer in the soil.
3. Take off the protective plastic bottle from the Tensiometer cup. Tilt
and pull the bottle off carefully. If necessary, carefully turn it counter-
clockwise!
4. Insert the T8 into the hole to the depth mark without using force.
In clayey soils a dangerous overpressure might
develop: Check the tensiometer's pressure reading
with an Infield measuring device or a data logger!
Important: Pay attention to the yellow sticker with
the dot on the shaft’s top end that marks the
position of the exit opening of the external filling
inside the cup:
a) Downwards installation: If the position of the cup
will be lower than the end of the shaft, the yellow
sticker must exactly face up!
b) Upwards installation: If the position of
the cup will be higher than the end of the
shaft, the yellow sticker must exactly face
down!
(a)

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External syringe refilling
Installed T8 can be refilled or ventilated through the
two capillary tubes (stainless steel) without being
removed from the soil. The tubes can be extended.
With the supplied refilling syringe a measuring range of
at least -80 kPa can be assured. With the special
Refilling Kit BKT456 a range of -85 kPa can be
assured.
Reference air pressure
The reference atmospheric air pressure is conducted
to the pressure transducer via the water impermeable
(white) Teflon membrane and through the cable.
The membrane must always have contact to the air
and should never be submersed into water.
Cable gland (IP67)
The T8 can be completely buried if required. Cables
and tubes of buried T8 should be protected. Special
cable glands are available for tight connection of a
cable protection tube.
Shaft
One-piece shafts from 10 cm to 200 cm are available.
Shafts over 200 cm are divided with threaded adapter.
Sensor body incl. electronics
Direct connection between internal power converter to
6-18 VDC
Pressure sensor
The piezoelectric pressure sensor measures the soil
water tension against atmospheric pressure
High grade porous ceramic cup
Filled with degassed water.
Temperature and level indicator
Optional protective plastic tube
Available as accessory

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5. Push down the shaft water retaining disk to a position directly on
the soil surface.
6. Slide on the thermal insulation tube over the capillary filling tubes.
7. If the plug is not connected right away leave the protective cap on
the plug. Water tightness is only assured when the plug is kept
clean.
8. Connect the Tensiometer signal wires as specified (see chapter
„ConnectingtheT8”)
The T8 can be connected to:
data loggers with analog input or serial RS485 or SDI12,
a PC or laptop via tensioLINK bus as a standalone sensor or
within a sensor network,
an additional 6 V Battery to run the T8 in the auto-logging
function (internal data logger, requires tensioVIEW software and
USB converter for configuration),
the INFIELD7 for taking spot readings or downloading stored
readings.
Please note:
Especially in loamy, clayey soils a high pressure can occur just by
inserting the T8 into the borehole. Thus, the pressure values
should be continuously observed during installation, either with the
INFIELD7 handheld or online with laptop, USB Converter and
tensioVIEW.
Note for the latter that the readings are refreshed only every 5
seconds by the internal microprocessor.
The less air is inside the cup and the better the soil's conductivity
is, the faster the Tensiometer will respond to tension changes.
If the soil is dryer than -90 kPa, it does not make sense to refill the
Tensiometer. The refilling procedure will be done best at the time
when the Tensiometer installed in the next lower level has reached
the value of drying off of the upper Tensiometer.

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2 Description of the T8
2.1 T8 parts
2.1.1 Body and shaft
The whole electronics are integrated in the body of the T8. The
housing is made of fiberglass reinforced plastic. The electronic is
completely sealed and thus well protected against moisture.
2.1.2 Pressure sensor
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 condensed water
inside the cable will leave the cable through the membrane.
The white membrane on the cable must always have contact to air
and should never be submersed into water.
2.1.4 Temperature sensor
A temperature probe with a tolerance of 0,2 K at 10 °C is used.
The tip of the temperature sensor dips into the Tensiometer cup's
water. Thus, the best possible thermal contact to the soil is achieved.

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2.1.5 Filling status indicator
The filling status indicator indicates the filling status of a T8 in a
downwards installation (cup lower than end of the shaft).
If the Tensiometer is installed in an upward angle (cup higher than
the end of the shaft), the water will still cover the indicator even if
air is already inside the cup. Thus, the indicator will react not
before the cup is almost completely empty (s. fig. 5.3 on page 38).
The filling status is determined by measuring the heat flux with the
internal temperature probe. For a probe dipped into water the heat
flux rate is lower than in air. If an air bubble appears around the
temperature probe, the heat flux rate rises and the insufficient filling
status is detected. This method offers a rough but reliable reference
for checking the filling and has the advantage of staying stable over
the whole lifespan of the Tensiometer. It replaces the previously use
IR-photo diode. The measurement of the soil water tension is not
influenced.
Benefits of the filling status indicator are an optimal service: If for
example mounting rails with integrated LEDs are used, the user can
check at a glance if all Tensiometers work well or which need to be
refilled.
Also, for quality assurance, the status of the signal can be logged for
later evaluation of the readings.
2.1.6 The ceramic cup
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 T8 cup consists of 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 is at least 1500 kPa (15 bar). If the soil is dryer than
1500 kPa 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.
The cup has a lifetime guarantee against breakage.

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2.2 Output signals
2.2.1 Analog
The T8 version 2005 has an internal microprocessor and offers water
tension and temperature as analog output signals plus the refilling
status as a digital signal.
Water tension and temperature are available as linear voltage
signals in a selectable range of 0...1 V, 0...2 V (default setting) or
0...5 V. Thus, the T8 are compatible to almost any data logger or
data acquisition system.
Furthermore, the measuring range itself can be set for special
measuring tasks. Standard is +100 kPa to -100 kPa and -30 to
+70°C.
Thestandardsettingforthefillingstatusiseitherswitch“open”(0V)
or“closed”(voltagesignal equal to power supply voltage).
2.2.2 Digital
To change the settings of signal range or use the serial interface of
the T8 the tensioLINK®USB converter with Windows software
tensioVIEW®is available as an accessory.
Filling status as a Digital Status
If the indicator detects an air bubble the indicator switch closes and
the supply voltage is available on the output. If for example a LED
with a series resistor is connected, the LED will light up to indicate
the necessity of refilling. In addition, or instead, connect the signal to
a digital or analogue logger channel to record the filling status for
quality control of the matrix potential readings.
2.3 Serial interfaces
The T8 has two serial interfaces: the RS485 compatible tensioLINK
interface and SDI12.

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2.3.1 tensioLINK®
To use the serial interface the tensioLINK®USB converter with
Windows software
tensioVIEW®is required.
tensioLINK®is RS485
based and used for all
functions, for taking
online readings, for
uploading stored data
and for configuration of
the T8.
RS485 allows a robust
and cost effective bus
linkage of sensors with
cables of up to a few
kilometers. Data loggers
with RS485 interface can
directly read sensors.
Please contact UMS for a
description of the data
protocol.
2.3.2 SDI12
Additionally a SDI12 interface is integrated for connection to SDI12
systems. The SDI12 interface has to be activated via tensioVIEW®.
Then, one of the 2 analog outputs is used as the SDI12 data line.

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2.4 Software
2.4.1 tensioVIEW
The Windows software tensioVIEW®(supplied with the tensioLINK-
USB converter) automatically detects all tensioLINK devices linked
within a bus network. The software is used for the configuration of
these devices and for displaying data.
tensioVIEW®shows for example the settings of a VS vacuum station
or T8 readings from the recent days.
When used in a laboratory no other device is required beside
tensioLINK, tensioVIEW and PC to have a complete data acquisition
system. Readings are displayed and stored by the PC directly.
2.5 Sensor logging
UMS Tensiometer T8 and TS1 have an internal non-volatile data
memory. When connected to a power supply readings of soil water
tension and soil temperature are taken and stored in selectable
intervals of 1 minute to 24 hours. The T8 has a capacity of 4000
readings which, with an interval of 1 hours, is enough for 166 days of
measurements.
In this mode of operation the power consumption is very low, so
modest battery capacities are
sufficient even for long
measuring periods.
To run stand-alone sensors a
battery box is available as an
accessory. The weatherproof
box is fitted with a tensioLINK
plug for uploading the data
stored in the sensor.

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3 Installation
3.1 Concept planning and installation
3.1.1 Selecting the measuring site
The installation spot should be representative for the soil horizon!
Therefore, in heterogenic soils, classifying drillings should be made
before or during installation.
On farmed sites with vegetation root spreading and root growth
during the measuring period must be considered. Fine roots will grow
around the Tensiometer cup as this is a poor but still secure source
of water. Therefore, avoid the root zone or move the Tensiometer
from time to time depending on the root growth.
Disturbing effects like waysides, the rim of a field, slopes or dints
must be avoided or considered in the interpretation of the measuring
results.
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 obtain a differential description of the soil water situation at least
2 Tensiometers are recommended per horizon, one in the upper and
one in the lower level.
Cable lengths of 100 meters and more are possible (see chapter 8.2
for cables) but should be avoided for the following reasons:
Accuracy: with a single-ended connection each 10 meter of
cable causes a reduction of the accuracy. (See chapter 3.3.1 for
compensation of current drop with single-ended connections)

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Lightning: cables act as antennas and should always be as short
as possible.
3.1.4 Protection of refilling tubes
A recent study by Prof. Wolfgang Durner showed that refilling
tubes must be protected from heating up and solar radiation.
If a bubble assembles inside a refilling tube, temperature changes
will lead to an expansion of the air resulting in a variation of the
reading. Therefore, refilling tubes should be as short as possible and
should be thermally protected, either by providing an insulating
protection or by burying the tubes.
Thermal effect:
As long as the Tensiometer and its tubes are freshly and completely
filled it will work perfectly. Any air trapped
inside the upper parts of the tube will expand
when heated up by solar energy. This causes
a drop of the water tension and some water
will flow from the cup into the ground.
Thus, readings will fluctuate around the actual
reading during solar radiation, especially with
low water potentials. Furthermore, under
permanent solar exposure the tubes get sticky
and brownish.
Slide the supplied thermal insulation tube over the shaft end , the
refilling tubes and sensor cable as shown in above photo. Please
keep a distanz of approx. 5 cm to the soil surface to avoid ant
population inside the tube!

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3.1.5 Jacket tubes
Jacket tubes are useful with shafts longer than 2 m, in pebbly soils or
gravel, and for horizontal installations from inside a well or pit hole.
The jacket tube should end 30 to 50 cm away from the cup so
leaking or condensation water is not conducted to the cup. The inner
diameter of the jacket tube should be at least 35 mm.
3.1.6 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). The more gravel in a soil the
more often the drilling has to be repeated to reach the required
depth.
3.1.7 Documentation
For every measuring spot you should:
Measure out the position where the pressure sensor will be
placed. (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 the 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 (see chapter 9.2).
3.2 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. Therefore, Tensiometers are preferably
installed at an angle.

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3.2.1 "Vertical" with downwards angle
When installed from the surface, an angle of 25° to 65° from the
vertical is optimal for refilling. In an absolutely vertical position air
bubbles might inside the edges of the cup adapter. Still, they could
be removed completely with the vacuum refilling kit BKTex. In this
position, the refilling tube is the shorter stainless steel tube with the
yellow sticker. Into this tube, water is injected for refilling.
Before inserting the Tensiometer, turn the shaft so the yellow
sticker near the shaft end points upwards.
Do not turn the shaft after it is inserted into the ground as this
might loosen the cup.
3.2.2 "Horizontal" or upwards installation angle
When installed horizontally or upwards from inside a well or pit hole,
the shaftmark must look downwards! An upward angle of approx. 5°
is ideal for refilling. Note that now de-airing and refilling tube are
switched: the refilling tube is the longer
stainless steel tube without the black
mark. Into this tube, water is injected for
refilling.
Before inserting the Tensiometer, turn
the shaft so the yellow sticker near the shaft end points
downwards.
Do not turn the shaft after it is inserted into the ground as this
might loosen the cup.
Note that with a horizontal installation the filling indicator will not
react much later, - if installed upwards not before until the cup is
almost empty.
3.3 Installation procedure
For the installation of the T8 in the field the following tools are
required:
Tensiometer auger with diameter 25 mm, ideally the UMS gouge
auger with shaped blade tip.
Rule, spirit level, angle gauge, marker pen.

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Minute book, camera for documentation of site and soil profile.
Perhaps PE-plastic bags for taking soil samples from the site.
Thermal insulation tubes for installations from soil surface.
Cable protection tubes.
Jacket tubes if required (inner diameter > 35 mm).
Please observe the following notes:
Do not touch the cup with your fingers. The ceramic should not
have contact with grease or soap as this will influence the
hydrophilic performance.
Do not leave the cup in air for more than 5 minutes as
Tensiometer water will evaporate and the Tensiometer will need to
be refilled.
Procedure:
1. Mark the required drilling depth on auger and Tensiometer shaft.
The reference point is the center of the cup. Drill a hole with the
desired depth on the chosen measuring spot. Auger stepwise
and take care when drilling the last 20 cm, remove and save this
soil. Water will not run along the shaft if the Tensiometer is
installed in an angle because the water will drain into the soil
before it reaches the cup.
Read the chapter "Selecting the installation position" for the best
installation angle.
2. When using augers with a diameter of over 25 mm, mix a paste
of water and crumbled soil material taken out of the borehole. Fill
the paste into the bottom area of the borehole by using a simple
pipe with outer diameter 2 cm.
3. Now take off the protective plastic cap from the Tensiometer cup.
Important: Do not turn, but pull when taking the bottle off - and
also when putting it back on again!
Save the plastic bottles: Do not store the Tensiometer without the
protective plastic bottle since the cup drains fast! The bottle must
be filled with some water for storage!