Rockwell Automation DeviceLogix System User Manual - Manual (Page 33)

Publication RA-UM003B-EN-P - February 2010 33
Navigate the Function Block Editor Interface Chapter 2
The above discussion outlined the general process of low-pass
filtering. Specifically, the filter discussed order 1 LPF and order 2 LPF.
Order 1 LPF
The target analog filter is as follows.
When bilinear transformation is applied, we take the w
p
as the actual
cutoff frequency. That is, the target transform function is as follows.
Then we apply the bilinear transformation.
Therefore, the corresponding difference equation is as follows.
Order 2 LPF
The target analog filter is as follows.
This is the same derivation process that is in order 1 LPF. Finally, the
corresponding difference equation is as follows.
where