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Service and maintenance
5.2 Testing
5.2.1 Calibration
When delivered Tensiometers are calibrated with an offset of 0 kPa
(when in horizontal position) and a linear response. The offset of the
pressure transducer has a minimal drift over the years. Therefore,
we recommend you check sensors once a year and re-calibrate
them every two years.
Return the Tensiometers to us for recalibration, or use the calibration
accessories available from UMS.
5.2.2 Check the Offset
With zero pressure difference between inside and outside of the cup
(cup in air) the signal should be 0 kPa.
There are two ways to check the offset.
1. Connect the Tensiometer to a readout device. Place the filled T8
in a beaker and fill the beaker with distilled or de-ionized water to a
height of 7,5 cm. Wait until the reading is stable. If there are bubbles
inside the cup this might take a while. The reading now should be
0 kPa.
2. To check the zero-point more precisely unscrew the cup. Shake
the pressure sensor to remove water from the pressure transducer
hole. The offset is acceptable when the reading is between -0,5 and
+0,5 kPa.
The pressure sensor diaphragm is inside the small hole on the
pressure sensor body. It is very sensitive and must never be
touched! It can be destroyed even by slightest contact! No
contamination should get on the sealing and gasket.
Before reassembling cup and sensor body carry out the degassing
procedure (see chapter 5.1.2 "Refilling in the lab").
For testing the signal gradient a calibration kit is required.
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