Siemens SIMATIC S7-200 System Manual page 430

S7-200 Programmable Controller System Manual
Input Calibration
The calibration adjustments affect the instrumentation amplifier stage that follows the analog
multiplexer (see the Input Block Diagram for the EM 231 in Figure A-17 and EM 235 in Figure
A-19). Therefore, calibration affects all user input channels. Even after calibration, variations in the
component values of each input circuit preceding the analog multiplexer will cause slight
differences in the readings between channels connected to the same input signal.
To meet the specifications, you should enable analog input filters for all inputs of the module.
Select 64 or more samples to calculate the average value.
To calibrate the input, use the following steps.
1. Turn off the power to the module. Select the desired input range.
2. Turn on the power to the CPU and module. Allow the module to stabilize for 15 minutes.
3. Using a transmitter, a voltage source, or a current source, apply a zero value signal to one
of the input terminals.
4. Read the value reported to the CPU by the appropriate input channel.
5. Adjust the OFFSET potentiometer until the reading is zero, or the desired digital data value.
6. Connect a full-scale value signal to one of the input terminals. Read the value reported to
the CPU.
7. Adjust the GAIN potentiometer until the reading is 32000, or the desired digital data value.
8. Repeat OFFSET and GAIN calibration as required.
Calibration and Configuration Location for EM 231 and EM 235
Figure A-15 shows the calibration potentiometer and configuration DIP switches located on the
right of the bottom terminal block of the module.
EM 231
Fixed Terminal Block
Figure A-15 Calibration Potentiometer and Configuration DIP Switch Location for the EM 231 and EM 235
416
↑On
↓Off
Gain Configuration
EM 235
Fixed Terminal Block Gain
↑On
↓Off
Offset Configuration