UGT Full Range Tensiometer User manual

Operating Manual
Full Range Tensiometer
Version: 20/07/20
Umwelt-Geräte-Technik GmbH
Eberswalder Str. 58 | D-15374 Müncheberg
phone: [phone] - 89 575 | fax: [phone] - 89 573
e-Mail: [email protected] | www.ugt-online.de

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Content
1. Introduction...................................................................................................................................... 3
1.1. Safety Instructions.................................................................................................................5
1.2. Scope of Delivery and optional accessories.............................................................................6
2. General Information ......................................................................................................................... 7
2.1. What are Tensiometers? / What is Tension? ..........................................................................7
2.2. What are Tensiometers used for?...........................................................................................8
2.3. How Does a Tensiometer Work? ............................................................................................8
2.4. Product versions..................................................................................................................10
2.5. Technical data......................................................................................................................10
3. Structure and basic functions ......................................................................................................... 11
3.1. structure..............................................................................................................................11
3.2. How to Operate the Full Range Tensiometer? ......................................................................12
4. Installation of the Full Range Tensiometer..................................................................................... 13
4.1. Preparation and Storage ......................................................................................................13
4.2. Installation of the Full Range Tensiometer ...........................................................................14
4.3. Interface and power supply..................................................................................................17
5. Data transfer ................................................................................................................................... 19
5.1. Measurement channels, bus addresses and data polling.......................................................19
5.2. Transformation digital signal in measurement value ............................................................25
6. Maintenance ................................................................................................................................... 27
6.1. Rezero of the Full Range Tensiometer ..................................................................................28

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1. Introduction
Thank you for choosing the Full Range Tensiometer. This manual can help you understand the Full Range
Tensiometer features.
Full Range Tensiometer by UGT covers the complete range of soil water tension relevant for plants,
that can reach up to 1500 kPa (pF 4.2) depending on the FRT version. Unlike other systems used for
this measuring range the Full Range Tensiometer doesn't determine the pressure head indirectly as a
derived variable, but via a direct pressure measurement. Even after drying out beyond the limits of the
measuring range, the measurement is continued independently as soon as the moisture increases
again. Refilling is not necessary. A further advantage compared to other measuring devices for the
complete plant relevant pressure head range is the low energy consumption (20 mA in operational
mode).
The measurement is reliable also in difficult media. Saline sites, such as in arid areas, are not a problem
as a result of the direct pressure measurement when correct calibrated.
The soil temperature is recorded as an additional parameter.
Advantages
•extended measurement range
•fast response
•maintenance free
•low power consumption

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There are several ways to contact UGT if you need a quote or product information please contact
Email: [email protected]
For any technical assistance or feedback or in case of problems with your product please contact
Email: [email protected]
We look forward to your inquiries or questions and are with pleasure at your disposal.
Phone:
+ 49 (0) 33432 –89 575
Fax:
+ 49 (0) 33432 –89 573
If contacting us by email or fax, please include as part of your message your instrument serial number,
your name, address, phone, and a description of your problem or question.
Please read these instructions before operating your Full Range Tensiometer to ensure that it performs
to its full potential.

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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 installing the tensiometer with high pressure
surges.
Protect from
high pressure
CAUTION
Sudden pressure drops inside the tensiometer may result in
permanent damage of the pressure transducer.
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
CAUTION
Grease, talc and solvents may influence the properties of the
ceramic cup. Aggressive media may affect the whole device and
leads 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
To remove or insert the tensiometer from or into the protective case
turn the tensiometer only to the right.
Use only clockwise
rotations

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1.2. Scope of Delivery and optional accessories
Basic
Optional equipment
•Full Range Tensiometer
•Protective case
•Cable for power supply and data
transfer, inclusive M12 connector
(standard length: 5 m, customizable)
•Installation auger
•Standpipe (length customizable)
•Datalogger
•Software (UGT-LOG)
Software (FRT-LOG)
Full Range Tensiometer
protective case
Cable for power supply
and data transfer
figure 1 scope of supply and optional accessories

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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.
PWP = permanent wilting point
FC = field capacity
)
figure 2 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. 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?
The operating principle of the Full Range Tensiometer differs slightly from water filled tensiometers.
Both kinds of tensiometers consist of an air-tight sealed, medium-filled measurement chamber, 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 liquid of the measurement chamber inside the
tensiometer with the water in the soil outside the tensiometer. By connecting the two liquid 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 chamber into the soil. In case of water filled tensiometers the measurement
volume is filled with water. Water that leaves the measurement volume via the pores of the ceramic
creates a negative pressure inside the tensiometer. 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.
In case of the Full Range Tensiometer the measurement volume is filled with water that is bonded to a
polymer.
figure 3 Schematic representation of the functional principle of a Full Range Tensiometer

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The measurement principle of the Full Range Tensiometer is based on a known pressure in the
measurement volume that is reduced by the soil tension.
The measurement range of conventional, water-filled tensiometers is physically limited by the boiling
point of water, which 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.
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.
The upper limit of the measurement range of a tensiometer is defined by which point is reached first. If
this tension is exceeded the tensiometer stops working.
Due to the bonding of water to the polymer the physical measurement limit of approximately 1 bar does
not account for the Full Range Tensiometer. The Full Range Tensiometer cannot run dry like water filled
tensiometers and is able to measure soil tensions up to 5 or 15 bar, respectively. For soil tensions out of
the measurement range the Full Range Tensiometer simply does not function properly. When the soil
tension is back in the measurement range, the Full Range Tensiometer simply starts to work properly
again. No refilling of the tensiometer is needed. Additionally, the Full Range Tensiometer also measures
the ambient temperature.

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2.4. Product versions
version 1:
Full Range Tensiometer FRT 5D
•Digital signal output: RS485
•Measurement range tension: -100 - + 500 kPa
(pF 3.7)
version 2:
Full Range Tensiometer FRT
15D
•Digital signal output: RS485
•Measurement range tension: -100 - + 1500 kPa
(pF 4.2)
2.5. Technical data
Technical Parameters
Measurement range Tension
-100 … 500 kPa (FRT 5D)
-100 … 1500 kPa (FRT 15D)
Operating temperature
+1… +39 °C (surrounding soil temperature)
Operating pH-value
pH 2 … pH 10
Power supply / Supply voltage
20 mA / 5 … 20 V
Interface output signal
RS485 / Analog output signal available on request
Dimensions
Ø25 mm, Length 150 mm
range of temperature during
calibration
4-30° C (at 100% water saturation)
Relative error within the
calibration range
+/- 0.5% (based on the entire measuring range)