First SLC 500 PID attempt

I've been reading the manual (SLC 500 Instruction Set) on
the PID instruction. The manuals directions for setting the
Kc term seem straightforward. However, for the Ti (reset) term
it states: "a rule of thumb is to set the reset time equal to
the natural period measured in the gain calibration" . I don't
know what is meant by "natural period". Is this the time span
between oscillation peaks when the gain is being set up?

basic idea:



suppose that you turn off both the Integral and the Derivative action ... suppose that you crank the Proportional action up to a high level ... suppose that you suddenly step the Setpoint from a low level up to a high level ...



the PV will start to oscillate ... the period of oscillation (from peak-to-peak) is often called the system’s “natural period” ...



here’s an example ...



now then ... whether setting the Integral/Reset action to the same “natural period” is a good idea or not is the subject of much debate ...

Try this site

http://www.controlguru.com

So far the information presented by the control guru is very good.

thanks for the explanation, Ron. I'll be finding out if it is
a good idea or not in my case week after next when we are set
up. Peter, I appreciate the controlguru url. I'll check that out
tonight.