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