Hardware and software signal filtering is supported in the DeltaV system:
The analog input card contains hardware filtering that limits the frequency of the input signal seen by the analog-to-digital (A/D) converter to about 3 Hz.
In addition, you can define software filtering to be applied at the analog card when you configure the analog input channel properties (FILTER channel parameter). This feature prevents aliasing of the signal if the module execution rate is set slower than twice the highest frequency component of the input signal.
The default setting for the software filter is Filter Disabled. If an input signal is relatively free of process noise and is contained in a module executing a moderately fast rate, you might not need to apply additional software filtering at the card.
If you choose to modify the filter, you see a selection of filter time constants in the Named State list. If you follow the module execution rate guideline (period of control) that is shown in parentheses next to the filter time constant you select, no aliasing will occur, even if the signal has significant noise.
If you modify the filter on an input channel, you might need to retune any control block that uses the channel for its controller variable.