66 Commissioning
WAGO-I/O-SYSTEM 750
750-496 8AI 0/4-20mA S.E.
Manual
Version
1.2.2
7.2.1
Example of Determining Gain and Offset
A two-point calibration method is used. Perform the following steps in WAGO-I/O-
CHECK
:
1. Select a sensor type.
In this example, sensor type 0 … 20 mA (ID1) was selected.
2. Activate user calibration.
3. Set the value for the calibration offset to “0”.
4. Set the value for the calibration gain to “1”.
5. Apply a 24 kOhm resistor in series with a ammeter to an I/O module channel.
Read the current of the measurement device and I/O module.
Example:
Reference current 1 (y1)= 0.9 mA
At 1 V is x1 = 0.915 mA
6. Apply a second 1.1 kOhm resistor in series to the same I/O module channel.
Read the current of the measurement device and I/O module.
Example:
Reference current 2 (y2)= 13.7 mA
At 9 V is x2 = 13.8 mA
7. Insert all read values into the respective equations to obtain the values for the
calibration gain and offset sought.
Example:
Calibration gain:
m = (y2 – y1) / (x2 – x1)
m = (13.7 mA – 0.9 mA)) / (13.8 mA – 0.915 mA) = 0.993
Calibration offset:
b = (y1 / m) – x1
b = (0.9 mA / 0.993) – 0.915 mA = −0.008 mA
8. Enter the value calculated for calibration gain (0.993) in WAGO-I/O-
CHECK
.
9. Convert the result for the calibration offset from milliamps to microamps.
10. Enter the value calculated for calibration offset in microamps (−8 µA) in
WAGO-I/O-
CHECK
.
