All analogue input channels (PD 640, PD 641, PD 642 and PD 643) have an integrated filter to remove the influence of 50Hz and 60Hz noise.

For further filtering, a filter can be activated with a time constant from 3 to 50 seconds.
This filter can be used to reduce fluctuations in the process signal. This could, for example, be due to disturbance in the contents of a tank caused by an agitator.

The filter constant defines that for a step change at the input terminals, the AnalogIn signal will have changed by 63% of the step process value after the period of the filter constant.