Effect of a low pass filter on the response of a PID controller

[skuntz]

In general terms, could someone please explain the effect that a low pass filter on the input of a PID controller would have on the response of the system? The controller will compare the process variable against a setpoint, but for reasons I'll not get into here, the process variable first goes through a low pass filter. Thank You.

 

[IRstuff]

Depends on the low-pass filter to some degree, but low-pass filtering is usually modeled as a time latency, so the response bandwidth should go down. If the latency is too large, the loop could be unstable.

TTFN
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[FeX32]

IRStuff has it on the money.

I have used in the past a "phase-compensator" to remedy inherent time delays caused in a system. In your case this latency could be caused by the filter, which can cause performance problems or instability.

A phase-lead compensator in s-domain is usually of the form
Comp(s)= (s+1/T)/(s+1/(alpha*T))

Cheers,


"Simplicity is the ultimate sophistication." L. da Vinci
- Gian