Umwelt-Geräte-Technik GmbH
| Eberswalder Str. 58 | D-15374 Müncheberg | phone: +49 (0) 33 43 2 - 89 575 |
3.2.
How to Operate the Full Range Tensiometer?
The Full Range Tensiometer starts measurements with an initial overpressure (P
ref
) inside the
measurement chamber, which is then reduced by the soil tension. The soil tension (
Ψ
) is thus calculated
based on the difference between P
ref
and the currently measured pressure inside the measurement
chamber:
𝛹 = 𝑝
𝑟𝑒𝑓
− 𝑝
𝑐𝑢𝑟𝑟𝑒𝑛𝑡
The overpressure in the measurement chamber is temperature dependent. In consequence P
ref
, which
was determined during the calibration process under specified temperature conditions, has to be
adjusted to the current measurement temperature. The calculation of P
ref
in equation 1 by using the
measured temperature is done via the following equation:
𝑝
𝑟𝑒𝑓
= 𝐶
𝑇1
∙ 𝑇
𝑐𝑢𝑟𝑟𝑒𝑛𝑡
2
+ 𝐶
𝑇2
∙ 𝑇
𝑐𝑢𝑟𝑟𝑒𝑛𝑡
+ 𝑃
0
Ψ … Tension [kPa]
p
ref
… Reference pressure, temperature compensated [kPa]
p
current
… Measurement value: pressure [kPa]
(
Transformation digital signal in measurement
value see chapter 5.3., equation 3 and 4)
𝑇
𝑐𝑢𝑟𝑟𝑒𝑛𝑡
… Measurement value: temperature [°C]
(
Transformation
digital
signal
in
measurement value see chapter 5.3., equation 3 and 4)
C
T1
… Temperature coefficient [kPa/
°
C
2
]
C
T2
… Temperature coefficient[kPa/
°
C]
P
0
… Reference pressure [kPa]
The parameters C
T1,
C
T2
and P
0
are determined and preset by UGT prior to delivery. Since they are unique
to each sensor, the parameters are noted in the calibration certificate. Due to aging of the polymer P
0
might be subjected to drift and should be calibrated regularly (see chapter 6). In individual cases, it might
be also necessary to re-calibrate the temperature coefficients C
T
. The calibration can be carried out by
trained UGT staff.
(1)
(2)
