WIKA DI30 - Manual (Page 25)

6 Commissoning, operation
WIKA operating instructions digital indicator model DI30 25
Sensor linearisation
In addition, non-linear sensors can be linearised with the aid of a
characteristic line that can be saved in the indicator. This is described with
the following example: The sensor signal must be parameterised in a strictly
monotonously manner, i.e. every new calibration point (e.g. PN104) must
have a higher input signal than the previous one (e.g. PN103) so that it is
taken over by the indicator. Otherwise, no confirmation will be shown. On the
other hand, the relevant indication values do not need to increase constantly.
They can also fall or alternate between rising and falling.
Example: Linearisation of a pressure transmitter (0...100 mbar) with output
0…20 mA.
To program e.g. 5 additional calibration points, “5” must be entered under
PN100.
Subsequently, for each of the calibration points, the voltage/current must be
applied to the unit and the respective indication value programmed under the
following program numbers PN101 - PN105.
The indicated value before correction can be either calculated from the known
characteristic line of the transmitter or determined empirically.
The non-linear range is between 0 ... 75 mbar. For calibration point 101, this
means:
A pressure of 15 mbar, the transmitter delivers 3.3 mbar instead of the ideal
value of 3.0 mbar. Since 20 mA in the display corresponds to 100.0 mbar, 3.3
mA in the display corresponds to 16.5 mA before the correction.
Setpoint
(PN)
Pressure
[mbar]
Output
transmitter
[mA]
Indication
before
correction (IN)
Desired
indication
(OUT)
2 0 0.5 2.5 0.0
101 15 3.3 16.5 15.0
102 30 6.2 31.0 30.0
103 40 9.2 46.0 40.0
104 60 11.4 57.0 60.0
105 75 14.7 73.5 75.0
1 100 20.0 100.0 100.0