UGT Tensio 100 User manual

Operating Manual
Tensio 100
Version: 29/05/18
Mobile Field Tensiometer
Umwelt-Geräte-Technik GmbH
Eberswalder Str. 58 | D-
15374 Müncheberg
phone: [phone] - 89 575 | fax: [phone] -
89 573
e-Mail: [e-mail] | www.ugt-
online.de

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Content
1. Introduction ........................................................................................................................................... 3
1.1. Safety Instructions............................................................................................................................... 3
1.2. Scope of Delivery ................................................................................................................................. 4
2. General Information .............................................................................................................................. 5
2.1. What Are Tensiometers? / What Is Tension?...................................................................................... 5
2.2. What Are Tensiometers Used For? ..................................................................................................... 6
2.3. How Does a Tensiometer Work?......................................................................................................... 6
2.4. Under Which Conditions Can a Tensiometer Be Used? ...................................................................... 7
3. Types of the Tensio 100 ......................................................................................................................... 9
4. Setup and Technical Specifications...................................................................................................... 10
4.1. Setup.................................................................................................................................................. 10
4.2. Technichal Specification .................................................................................................................... 12
5. Accessories........................................................................................................................................... 13
6. Initial Operation ................................................................................................................................... 13
7. Measurement....................................................................................................................................... 14
7.1. Installation of the Tensiometer......................................................................................................... 14
7.2. How to Read Out Data?..................................................................................................................... 15
7.2.1. Tensio 100..................................................................................................................................... 15
7.2.2. Tensio 100 RFID............................................................................................................................. 15
7.2.3. Tensio 100 RFIDplus ...................................................................................................................... 16
7.3. Optimizing the Application................................................................................................................ 16
7.3.1. Verification of the Measurement Values...................................................................................... 16
7.3.2. Profile Measurements .................................................................................................................. 17
7.3.3. Reducing the Measurement Time ................................................................................................ 17
8. Care and Maintenance......................................................................................................................... 17
8.1. General Care and Storage Instructions ............................................................................................. 17
8.2. Filling and Degassing of the Tensiometer ......................................................................................... 18
8.3. Replacing the ceramic and the O-rings ............................................................................................. 20
9. Troubleshooting................................................................................................................................... 22

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1. Introduction
The warranty orients itself on the statutory regulations. Specifications can be found under item 7 to 9
in our general business terms and conditions. Contact us via telefax or email if you discover any faults
or defects.
1.1. Safety Instructions
Tensiometers are measurement devices for the determination of soil water tension and should only be
used for that purpose. Please note that damage due to improper handling may not be covered by
warranty.
Please attend to the following safety instructions for your own protection and for maintaining the full
functionality of the device:
CAUTION
Freezing of water within the tensiometer may result in permanent
damage of the tensiometer. Make sure
to store the tensiometer
in a frost-free environment. At temperatures below 0° C the
tensiometer should not be used for measurements.
Protect from
frost
CAUTION
High pressure may lead to permanent damage of the pressure
transducer. Avoid
compression of trapped media during
installation or when putting on protective caps. The tensiometers
are not suitable for use in a triaxial shear test apparatus.
Protect from
high pressure
CAUTION
Sudden pressure drops inside the tensiometer may result in
permanent da
mage of the pressure transducer. Do not open the
screw plug
when a negative pressure is applied inside the
tensiometer.
This accounts for all available types.
Protect from sudden
pressure drops
CAUTION
Mechanical forces may result in damage of the ceramic and/or the
pressure transducer. Prevent jolting or hard hitting as well as
partial pressure on the ceramic by rocks in the soil
.
Protect from
mechanical forces

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CAUTION
Grease, talc and solvents may influence the properties of the
ceramic. Aggressive media may affect the whole device and lead
to permanent damage. Do not touch the ceramic with bare hands.
Use only pure water and no detergent for cleaning.
Protect from
chemical influences
CAUTION
Turning the manometer/pressure transducer may influence the
tightness of the tensiometer.
Avoid turning the manometer
during transport or measurements, especially when using the
manometer version of the Tensio 100.
Do not twist
pressure transducer
1.2. Scope of Delivery
•Tensiometer Tensio 100, Tensio 100 RFID or Tensio 100 RFIDplus according to order, ready to use,
filled and calibrated
•RFID handheld device for Tensio 100 RFID or RFID/USB reading cable for Tensio 100 RFIDplus
including software
•Insertion auger for easy installation and optimum soil contact, standpipe length as ordered, fitting
for protection tube
•Protection tube with locking screws and sponge for easy transport of tensiometer and insertion
auger, for protection against mechanical damages of the tensiometer, and for preventing the
tensiometer from drying to keep it ready for use
•Operating Manual „Tensio 100 –Mobile Field Tensiometer“

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2. General Information
2.1. What Are Tensiometers? / What Is Tension?
Tensiometers are measurement devices for determining the soil water tension. The soil water tension
describes all influences exerted on the water by the soil matrix and is also called the matrix potential
(or simply pressure head). The tension is defined as a negative pressure and therefore is signed
positive if the applied pressure is negative. A pressure of -50 kPa in the pore water accords a tension of
50 kPa.
The tension is closely linked to the water content of a soil. The dryer a soil, the higher is the tension. At
the groundwater surface, the tension is zero. The relationship between water content and soil tension
is soil specific and depends highly on the soil properties.
Abbildung 1: Exemplary retention curves of different soil types

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2.2. What Are Tensiometers Used For?
The tension corresponds to the force which a plant has to apply via the roots to extract water from the
soil pores. Among other applications, tensiometers can be used for irrigation control and for
evaluations of global warming impacts on ecosystems. The difference between the tensions at two
points within the soil acts as the driving force for soil water transport. Determining this gradient by
using tensiometers enables the evaluation of water movement in the soil regarding flow direction and
velocity. Tensiometer measurements are essential for the comprehensive analysis of the water balance
of a region or an ecosystem.
2.3. How Does a Tensiometer Work?
A Tensiometer consists of an air-tight sealed, water-filled measurement volume, a unit where the
pressure transducer is located, and a porous cup, usually made out of ceramic. The pores of the
ceramic cup are filled with water and connect the water of the measurement volume inside the
tensiometer with the water in the soil outside the tensiometer. By connecting the two water bodies
the pressure conditions inside the tensiometer are always adjusted to the pressure conditions of the
water in the surrounding soil. If the soil dries, water will flow through the pores of the porous
tensiometer cup from the measurement volume into the soil, thereby creating a negative pressure
inside the tensiometer.
The water flow equilibrating the pressures goes on until the negative pressure in the measurement
volume corresponds to the negative pressure in the surrounding soil. If the surrounding soil is wetted
again, for example by a precipitation event or irrigation, the negative pressure decreases in the
surrounding soil and water flows from the soil into the measurement volume, whereby the negative
pressure in the measurement volume is reduced again. A manometer or an electronic pressure
transducer measures the pressure inside the measurement volume. Depending on the tensiometer
type and design of the tensiometer the pressure is either read manually or captured automatically,
whereby the reading unit as well as the storage unit can be integrated in the tensiometer or externally
executed. Tensiometers are calibrated in a way that the measured pressure is zero when the porous
cup is right at the level of the groundwater surface. For the Tensio 100 tensiometers this calibration
only applies for vertical installation. The water-filled volume in the standpipe acts as a hanging water
column and applies an additional negative pressure on the pressure transducer. The tension value at
the ceramic tip and the pressure at the pressure transducer differ by this negative pressure. To
compensate the influence of the hanging water column, the pressure transducer is calibrated
accordingly. Since this pressure difference depends on the height difference between ceramic cup and
pressure transducer and therefore on the installation position, deviant installation angles result in
incorrect measurements.

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2.4. Under Which Conditions Can a Tensiometer Be Used?
Based on the operating principle the measurement range of conventional, water-filled tensiometers is
physically limited by boiling of the water. The boiling point of water (according to standard 99.6 °C at
1013.25 hPa ≈ 1 bar) is pressure- and temperature-dependent. The boiling point inside the
tensiometer and thus the upper limit of the measurement range depends on the ambient atmospheric
pressure and ambient temperature. At 20 °C and 950 hPa barometric pressure the water starts boiling
at approx. -926.6 hPa. This value also depends on the temperature-dependent vapor pressure, which
rises with increasing temperature. Thus higher ambient temperatures and lower barometric pressure
reduce the measurement range of a tensiometer. This point may be delayed by boiling retardation.
From this moment on the pressure change is not longer transferred from the water in the soil.
The second physical limit is defined by the air entry point of the ceramic. This point is reached when
the negative pressure is high enough to suck air through the biggest pore of the ceramic. At this
moment the system is not air-tight anymore and the negative pressure suddenly drops. Subsequently
the tensions are about zero and it is not possible to build up a negative pressure again.
The upper limit of the measurement range of a tensiometer is defined by which point is reached
sooner. If this tension is exceeded and the measurement range is left, the tensiometer stops working.
This is called “drying up” of the tensiometer. To restore the functionality of the tensiometer it needs
to be refilled with water and the tension in the surrounding soil has to be within the measurement
range of the tensiometer. Some systems, such as the Full Range Tensiometer of UGT GmbH, are not
bound to these limits and cannot fall dry due to innovative operating principles.
Water
Porous Cup
Soil Particle
Air
Water
Abbildung 2 Schematic representation oft he functional priciple of a tensiometet

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The ceramics of the UGT tensiometers have by default an air entry point of at least 85 kPa. This value
slightly varies for every ceramic and depends next to the maximum pore size also on the state of the
ceramic and on substances dissolved in the water. Therefore, a common minimum values is stated as
upper limit of the measurement range. This value may be exceeded during measurements.
Abbildung 3 Exemplary tension curve with the limits of the measurement range, phase change and air entry point
Another prerequisite for the correct function of tensiometers is the correct installation. The porous
cup needs to be in good contact with the soil to connect the pore system of the soil and the porous
material. Tensiometers should be installed in moist soil, if possible. When using an auger for the
installation, the diameter of the borehole must be slightly smaller than the diameter of the porous cup.
During installation the mechanical force on the ceramic cup needs to be kept as low as possible.
Obstacles, such as rocks in the soil may result in cracks or fractures in the ceramic cup. This may cause
the system to leak and therefore not to be functional anymore. Please refer to the according chapters
of this manual for detailed and tensiometer-specific information on the installation and maintenance
of the tensiometers.
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
Pressure [kPa]
Exemplary Tension Curve
Increasing tension within the
measurement range
Phase change
liquid gaseous
Air entry point of
the ceramic

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3. Types of the Tensio 100
The Tensio 100 product line offers a range of tensiometers for the fast and easy in-situ determination
of the tension. Their design in combination with the auger included in the set allow for a rapid
installation of the tensiometers without any additional tools or great installation effort. Due to the
specific ceramic cup and the pre-loading screw the response time is less than 3 seconds. Stowed in the
protective tube auger and tensiometer can be carried easily and safely and are always ready for use.
In adaption to different applications the Tensio 100 is available in three different types, which differ in
the type of the used pressure sensor.
Tensio 100 – with mechanical manometer
•displays the current tension on a mechanical Manometer
•simple and cost-efficient system
•ideally suited for teaching purposes, since the operating principle is clearly understandable
•the diagram printed on the back of the tensiometer head enables a fast classification of the
measured values even without extensive expertise
•very suitable for short-termed measurement campaigns with many measurement points, such as
mapping the current tension allocation or checking and optimizing the state of irrigation in
agriculture as well as for concomitant reference measurements for other sensors (e.g. soil
moisture) or as basic information for sampling
•no data logging
•not suitable to remain in the field
Tensio 100 RFID
•displays the current tension on an electronic handheld device, which receives the data of an
electronic pressure transducer via RFID
•the displayed data are stored on the handheld device and are available as a digital data set
•very suitable for capturing short-term tension changes over a period of up to one day
•very suitable for determining the short-term reaction of a soil/eco system to an event and for
estimating the water movement in the soil
•very suitable as concomitant measurement for infiltration tests
•suitable to remain in the fields
•no automated data logging
Tensio 100 RFIDplus
•data recording with an electronic pressure transducer and storage on an integrated data logger
•the data can be transferred to a laptop or PC via an RFID adapter using the USB port
•very suitable for capturing medium-term tension courses over periods of up to several months
•very suitable for measuring campaigns with changing measurement points, for example for
preliminary investigations as a basis for planning new measurement sites / project concepts

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4. Setup and Technical Specifications
4.1. Setup
Tensiometer head
Tensio 100 Manometer
Tensio 100 RFID Pressure Transducer
Tensio 100 RFIDplus Pressure Transducer
Plug screw
Pre-loading screw
Ceramic cup
Tensiometer tip
O-Ring
Standpipe
Abbildung 4 Setup of the Tensio 100 tensiometer

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The ceramic of the Tensio 100 is placed at the lower end of the standpipe on an internal core. Two
rubber O-rings seal the ceramic against the stainless steel. The lower end of the standpipe is closed by
a stainless steel tip. This tensiometer tip is connected to the standpipe with a screw thread and can be
screwed off to exchange the ceramic cup and/or the O-rings. The standpipe can either have one of the
standard length (30 cm / 60 cm / 90 cm) or a customized length to choose freely. The standpipe is
hollow and completely filled with water when in a ready to use state. The internal space of the
standpipe connects the ceramic with the pressure transducer at the tensiometer head. Depending on
the type of Tensio 100 the pressure transducer is either a precision vacuum meter, an electronic
pressure transducer without integrated data logger, or an electronic pressure transducer with
integrated data logger. The tensiometer head is made of clear acryl glass. On the top side of the
tensiometer head is a plug screw with a groove. Unscrewing this plug screw connects the internal
space of the tensiometer with the atmosphere. On the side of the tensiometer head is a pre-loading
screw for increasing the internal space by unscrewing it. On the back of the tensiometer head a chart
with standard values for a rough estimate of the displayed tension is imprinted.

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4.2. Technichal Specification
Tensio 100
Tensio 100 RFID
Tensio 100 RFIDplus
Pressure measurement
Precision
vacuum-meter
Electronic pressure
transducer
Electronic pressure
transducer
Measurement range
0 … -85 kPa
0 … -85 kPa
0 … -85 kPa
Output unit
bar
bar
bar
Accuracy
0,01 bar
±0,0045 bar
±0,0045 bar
Resolution
0,01 bar
0,001 bar
0,001 bar
Data output
Manual reading
Display and storage on
handheld device
Display and storage on
Laptop/PC
Interface
/
RFID-Handheld device
RFID/USB
Data memory
/
/
Approx. 2048 pressure and
temperature data sets
with time stamp
Power supply
/
External via RFID-
Handheld device
Integrated battery
Lifetime at 25 °C approx.
4…5 years with
permanently 1
measurement per minute
Storage life at 25 °C
approx. 10 Years with a
self-discharge of approx.
1% per year
Degree of protection
IP54
IP67
IP67
General
Response time according
to RICHARDS
< 3 s
Operating temperature
0 … 40 °C
Ceramic
Length
24 mm
Diameter
10 mm
Air entry point
> -85 kPa
Hydraulic conductivity
8.1x10-8 m/s
Standpipe
Length
30 cm / 60 cm / 90 cm / customized on request
Diameter (outer)
10 mm
Material
V2A stainless steel

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5. Accessories
Optionally Available Accessories
Protective cap
Protects the ceramic cup from drying out and mechanical damage
V2A-Insertion auger
Non-destructive and simple installation of the tensiometers and
optimum connection to the pore system of the soil
Extension for insertion
auger
For optimum installation of the tensiometers in greater depths.
Enables the adjustment of the auger to
different standpipe
lengths.
Ceramic cup SKA 100 FF
Replacement ceramic cup for Tensio 100 / Tensio 150 /Tensio 160
; ø 10 mm, length 24 mm
6. Initial Operation
The Tensio 100 is delivered water-filled and ready to use. A specific initial operation is therefore not
necessary. Before every application the following points should be checked to ensure accurate
measurement results.
•Check if the ceramic cup is screwed on tightly and slightly screw in the tensiometer tip to
tighten it if necessary
•Check the tightness of the tensiometer by creating a negative pressure in the tensiometer by
unscrewing the pre-loading screw. If air enters the tensiometer or the negative pressure cannot
be sustained, find and fix the leak.
•The tensiometers must be checked for entrapped air and degassed if necessary. A detailed
instruction on how to degas the tensiometer can be found in chapter 8.2 of this manual.
Attention!
Thereby do not touch the ceramic cup with bare hands. Use gloves or paper towels to
prevent direct contact between skin and ceramic.

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7. Measurement
The above warning accounts only for the use of the Tensio 100 tensiometer with mechanical
manometer. Both of the RFID types have a protection degree of IP67 and are water proof up to
temporary submersion. Thus, the RFID types are able to remain in the field and are preferable to the
manometer type in expectation of very humid conditions.
7.1. Installation of the Tensiometer
•Identify a suitable measurement location. In general a high amount of soil skeleton is
unfavorable.
•Use the supplied auger or according soil augers to pre-drill to the designated measurement
depth.
Attention!
The Tensio 100 is splash-proof and can therefore also be used for measurements under wet
conditions. However, make sure to dry the tensiometer immediately after contact with water to
prevent water entering the manometer. There must be no water accumulated on the glass of
the manometer. The Tensio 100 is not suitable to remain in the field. Permanent moisture can
cause irreparable damage to the manometer.
Note
To ensure good contact between the ceramic cup and the soil the installation hole
should be about 2 cm shorter than the designated measurement depth. The
tensiometer is pushed into the soil for the remaining 2 cm.
Note
Pay attention to resistance while pre-drilling. This can be a first indication for rocks or
other obstacles in the soil. If you feel a considerable resistance, stop the pre-drilling
and try it again some centimeters apart.
Attention!
Mechanical stress through rocks and other obstacles in the ground can damage the drill
as well as the ceramic of the tensiometer.
Note
The tensiometer is factory calibrated to a vertical installation. Thus, the borehole
needs to be prepared vertically.

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•Take the tensiometer out of the protective tube and wipe off adherent water drops with a rag
or a sponge.
•Carefully push the tensiometer into the prepared borehole.
7.2. How to Read Out Data?
7.2.1. Tensio 100
The tension can be read on the manometer as soon as the pointer has come to a standstill. To
verify the measurement, slightly screw out the pre-loading screw to create a negative pressure
and wait until the manometer shows a stable value again. For a correct measurement both values
have to be similar.
7.2.2. Tensio 100 RFID
The current tension can be displayed and stored on the
RFID handheld device. Switch on the handheld pushing
the „ON/OFF“-button. Hold the device towards the
sensor and push the read-button .
The current pressure value is shown on the display. Push
the read-button repeatedly and compare the values. If
the values are stable, the state of equilibrium between
tensiometer and soil water is reached and the displayed
pressure value accords the current tension.
Pushing the -button toggles between the pressure value and the temperature value. The pair of
values is automatically stored on the handheld device when reading.
Abbildung 5: RFID Handheld device for reading
the data of the Tensio 100 RFID
Attention!
The tensiometer may not be screwed into the soil, as this may loosen the ceramic cup.
Note
Do not leave the tensiometer outside the protective tube. Being exposed to air it will
dry out fast.
Attention!
Pushing the tensiometer into the soil may cause an overpressure in the tensiometer
which may damage the pressure sensor. Especially for soils with poor hydraulic
conductivity, such as clay, the tensiometer has to be pushed in very slowly.

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7.2.3. Tensio 100 RFIDplus
Unlike as for the other types, for the Tensio 100 RFIDplus
the measurement must be explicitly started. The
communication with the sensor happens via an RFID-pen,
which is connected to the laptop using a USB port and the
corresponding software. The software is included in the
scope of delivery and must be installed on the laptop
before the first use. It can be installed on any number of
systems, that any laptop can be used for reading the data.
Plug the RFID-pen into the USB port of your laptop. Start the software on your laptop. Start a new
measurement and hold the tip of the pen to the black face of the sensor. Starting a measurement
the measurement interval can be chosen and the measurement series can be named. After that
the sensor independently measures the pressure and the temperature with the set interval and
stores them on the data logger. To read the data, stop the measurement and hold the tip of the
pen to the sensor again. The retrieved data are automatically shown as graph in the software. The
data series is available as a .csv file and can easily be processed in spreadsheet programs.
The Tensio 100 RFIDplus can remain in the field for several months. The data can be read at any
time. However, directly after installation the response time until equilibrium must be considered.
7.3. Optimizing the Application
7.3.1. Verification of the Measurement Values
The heterogeneity of the soil, as well as location differences (vegetation differences, local depressions,
compaction, etc.) affect the measured tension values. These influences must be considered when
evaluating the data. Multiple measurements in the immediate vicinity of a measuring point help to
identify outliers and confirm the measured values statistically. Measurements at different
measurement points with largely the same properties in a target area provide an average and reduce
the influence of inhomogeneities in the soil.
Also check the material excavated with the insertion auger as indication on two soils being
comparable.
Measurements at different points with different site characteristics help to quantify the influence of
these characteristics. For example measurements in immediate vicinity of the root zone of a plant and
apart from the root zone or measurements in compacted soil of a track and in the non-compacted soil
next to the track.
Figure 6: Reading the pressure transducer of a
Tensio 100 RFID
plus with the RFID-pen

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7.3.2. Profile Measurements
The Tensio 100 can also be used to determine tension profiles by successive measurements at
different depths. Start at the measurement point closest to the soil surface and successively proceed
to the deeper measurement points up to the deepest profile point.
Prepare the installation hole to the designated depth and install the tensiometer. Wait for the
measurement to be finished, retrieve the tensiometer from the soil and deepen the already existing
installation hole with the auger up to the next measurement depth. It is helpful to measure and mark
the designated depths at the auger and the tensiometer (e.g. with tape or permanent marker). Be
aware that the measurement does not happen at the tip of the tensiometer but at the ceramic part.
Further, it should be considered that the depth of the prepared borehole must be smaller than the
final installation depth to ensure a good contact between soil and ceramic by pushing the ceramic into
unprepared soil.
7.3.3. Reducing the Measurement Time
Experienced users may use the pre-loading screw to reduce the response time and thereby the overall
measurement time. This is especially suitable for very dry soils, since in that case the pressure
difference between the initial value in the soil and in the tensiometer is very high. Thus, a high amount
of water needs to be transferred from inside the tensiometer into the surrounding soil to achieve the
equilibrium. This process not only extends the measurement time, but may also influence the tension
in the immediate vicinity of the ceramic part by releasing the water into the soil.
The pre-loading screw allows minimizing this effect. Note the displayed pressure right after the
installation and carefully unscrew the pre-loading screw until about 1.5 times the initial value is
displayed. Observe the progress of the displayed pressure values for about 30 seconds. If the pressure
keeps increasing the equilibrium has not been reached. Increase the pressure by 5 to 10 kPa and again
observe the reaction of the pressure values. Repeat this step as necessary to rapidly approach the final
value. If the pressure decreases after unscrewing the pre-loading screw, the current tension in the soil
was exceeded. In that case wait until the value is stable.
This gradual approach to the final value is recommended if the expected tension is unknown as it
prevents unnecessary exceeding of the tension.
For a known soil that allows a good estimation of the tension, already a reasonable estimate of the
tension may be preset by unscrewing the pre-loading screw to reduce the measurement time.
8. Care and Maintenance
The Tensio 100 tensiometers are largely maintenance-free and factory calibrated. They do not require
regular maintenance or calibration routines. However, suitable maintenance and storage can increase
significantly the functionality and the life-time of the instrument.
8.1. General Care and Storage Instructions
•The tensiometer should always be stored and transported in the provided protection tube to
protect it from damage due to mechanical stress.

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•The sponge in the protection tube must be wet at all times to keep the tensiometer ready for
use.
•The Tensiometer must always be protected against frost. Both, storage and measurement at
temperatures below 0 ° C can lead to permanent damage of the tensiometer.
•After measurement, clean the tensiometer tip and the ceramic part with a sponge to remove
adherent dirt.
•To clean the ceramic cup, push water from the inside through the ceramic by screwing in the
pre-loading screw while the ceramic is in water.
•The tensiometer tip must not dry up being un-cleaned.
•If necessary, the top layer of the ceramic cup can be sanded gently with fine wet sandpaper.
8.2. Filling and Degassing of the Tensiometer
Normally the Tensiometer must only be degassed to remove air bubbles before use. If the
tensiometer fell dry (no water visible in the tensiometer head) due to wrong storage, repair or
very dry soil it needs to be completely refilled to restore functionality.
The process is the same for both cases, but must be repeated more often for a complete filling.
Therefore, the work sequence described below applies to both processes.
Deviating for refilling very long tensiometers a hand pump can be connected in place of the
screw to apply the necessary negative pressure more easily.
Approximately 1 L of distilled water is needed. To avoid the occurrence of air bubbles at strong
negative pressures the water may additionally be degassed.
Preparation:
If the ceramic part was completely dry it should be soaked in distilled water for at least 12
hours before refilling. If the tensiometer has not been used for a longer period the O-rings and
the ceramic should be checked for damages and replaced if necessary. More information on
changing the ceramic and the O-rings can be found in the according chapter of this manual. The
ceramic should be clean. If necessary, clean the ceramic with a wet sponge or carefully sand the
top layer with fine wet sandpaper. Make sure not to touch the ceramic with bare hands. For
sanding, the ceramic should already be soaked.
Step 1: Unscrewing the pre-loading screw
Attention!
The tensiometer should only be filled with distilled water to maintain the functionality of the
ceramic.
Attention!
The screw must be turned out maximum that far the sealing ring does not touch the
thread.

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Unscrew the pre-loading screw up to a half.
Thereby a negative pressure is created which is
displayed on the manometer/via the pressure
transducer. Existing air bubbles inside the
tensiometer expand.
-The ceramic cell has to be dry because otherwise
it s not airtight enabling air to be sucked into the
tensiometer and precluding the negative
pressure. Wipe the ceramic dry with a soft cloth
if necessary.
-If air bubbles enter at the pre-loading screw the
sealing ring is either unscrewed too far or
damaged
-If repeatedly air bubbles emerge from the
standpipe the ceramic cup should be tested for
leaks. Most frequent causes for leaks are wet
ceramic cups, loose ceramic cups or damaged
ceramic cups. If the ceramic cup is damaged it
needs to be exchanged.
Step 2: Refill water
To refill water the tensiometer with the applied
negative pressure is put into distilled water. The
ceramic cup has to be completely submerged.
-The negative pressure sucks the water through
the ceramic into the tensiometer. Therefore the
negative pressure displayed on the
manometer/pressure transducer decreases.
-Leave the tensiometer in the water until the
displayed pressure is back to 0.
-The tensiometer must be in a vertical position.
-Secure the tensiometer against falling over
during the filling process. A big, heavy water-
filled vessel allows for the tensiometer to stand
freely.
-To fill several tensiometers at once they can be
put in one vessel together.
Pre-loading screw
Plug screw

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Step 3: Open plug screw
Open the plug screw by approximately 2 turns.
The notch in the screw connects the atmosphere
to the internal space of the tensiometer.
Step 4: Screw in the pre-loading screw
Screw in the pre-loading screw completely. In doing so, air bubbles are pressed out of the
tensiometer through the notch of the plug screw.
Step 5: Close the plug screw
Screw the plug screw back in completely to seal the tensiometer.
Step 6: Repeat if necessary
Repeat steps 1 to 5 if there are still air bubbles visible inside the tensiometer head.
8.3. Replacing the ceramic and the O-rings
Step 1: Unscrew the metal tip
Turn the stainless steel tip counterclockwise to screw it off. After screwing off the metal tip, the
ceramic and the O-rings can be removed from the supporting bar
Step 2: Screw in the supporting bar
Attention!
The ceramic part has to be in the water when the plug screw is being closed and the
screw must be screwed in slowly to avoid overpressure on the manometer/ pressure
transducers.
Notch
visible
Usually, only the ceramic is broken, so the
already-mounted supporting bar can be further
used. But, as this may have become loose while
unscrewing of the ceramic tip, always check for
the correct position of the supporting bar
before putting on a new ceramic.
Spigot
Supporting bar