How to calibrate analog input module plc

plc analog input modules Some plc hardware calibration method, some use software calibration method, should prepare high-precision calibration of measuring instruments and stable input signal source, the number of samples to be taken as the average of the filtered larger value.
Hardware calibration method. S7-200 with EM235 analog input module, for example, analog input module has an offset adjustment potentiometer. Because only 0-20mA EM235 when the 4mA current applied to the input of a channel, read digital converted by programming software, adjust the offset potentiometer until the reading of 6,400.