22
Installation
SWT4 User Manual v3.1
Example 1:Using
A 5 cm vertical column of water below the pressure
sensor will create an 0.5 kPa offset. This means that when the soil
water tension is 0 kPa the sensor will indicate -0.5 kPa.
Table showing the offset correction when a 5 cm column of water is
tilted at various angles:
Angle to vertical line
0°
10°
15°
20°
25°
30°
Offset correction in [kPa]
+0.5
+0.49
+0.48
+0.47
+0.45
+0.43
Angle to vertical line
45°
60°
70°
75°
80°
90°
Offset correction in [kPa]
+0.35
+0.25
+1.7
+1.3
+0.9
0
The offset is entered as + in your logger if you regard the soil water
tension to be negative (0 ... -85 kPa).
3.4.1 How to measure the zero offset of a tilted
tensiometer
As an alternative to using the table above, if the tensiometer is to be
installed pointing downwards, submerge it up to one half the height of
the ceramic cup in a beaker of water, tilting the tensiometer to the
desired angle. The data logger reading in mV now represents 0kPa
water tension at that angle, giving you the zero offset correction
directly.
