Rockwell Automation 20D PowerFlex 700S with Phase I Control Reference Manual - Manual (Page 55)

Rockwell Automation Publication PFLEX-RM002D-EN-E - August 2013 55
Detail Drive Configuration and Operation Chapter 1
Low Pass Filter
A low pass filter is designed to pass low frequencies and attenuate high
frequencies. The break point between high and low is called the cut off
frequency.
Figure 13 - Bode Plot Low Pass Filter (wco = 10 rad/sec)
The Process Control Loop has a low pass filter immediately after the error signal.
The break frequency is set by parameter 184 [PI Lpass Filt BW]. The filter is
used to eliminate unwanted noise in the feedback. Typical range is between 10
rad/sec to 50 rad/sec.
Second Order Low Pass Filter
A second order low pass filter is similar to a low pass filter, however the
magnitude rolls off twice as fast as a first order low pass filter. Also the phase shift
of a second order filter is from 0…180° compared to 0…90° of a first order filter.
Figure 14 - Second Order Low Pass Filter