Rockwell Automation 2080-LC20-20QBBR Micro820 20-point Programmable Controllers User Manual - Manual (Page 150)

142 Rockwell Automation Publication 2080-UM005A-EN-E - December 2013
Appendix D IPID Function Block
IMPORTANT
User Program Scan Time is Important
The autotuning method needs to cause the output of the control loop to
oscillate. In order to identify the oscillation period, the IPID must be
called frequently enough to be able to sample the oscillation adequately.
The scan time of the user program must be less than half the oscillation
period. In essence the Shannon, or Nyquist-Shannon, or the sampling
theorem must be adhered to.
In addition, it is important that the function block is executed at a
relatively constant time interval.