Pid Loop Setup in PLC

The Plc Kid

Member
Join Date
Feb 2009
Location
Macon, Georgia
Posts
3,233
Hi everyone.

I am looking at moving a psi control loop that is currently ran by a single loop psi controller into a slc 5/04 pid loop.

My problem is i don't know where to begin as far as tuning it.

Where would i get initial values for the pid instruction and which values are more critical thatn others?

Max operating psi is about 1600 psi and high limit is 2500 psi low limit and output min is 0 psi.Would 1600 psi be my output cv% max?

How can i get values for gain kc,reset ti,rate rd,loop update,deadband.

Default control mode is E=SP-PV is this correct?

What about time mode default is sti. What is sti?

I have read the instruction help and i am still lost.

Can someone give me some direction please.
 
Kid,

Most of the values you're concerned with typically come from trial and error test of the loop. Pressure loops are usually fast acting, and easier to tune. My typical methodology(right, wrong, or otherwise) is to begin with only Kp. I double this until I see oscillation around the setpoint. I then back it off until I reach the point at which the Kp alone will stabilize the error, but may not force the error to 0. Then I begin adding small amounts of Ki to taste. There are tons of examples, and several other proven methods for this subject. Most are probably better than the quick explanation I've given.

I don't have access to Logix500 in front of me, but if your loop is direct acting(increase in PID output = higher pressure), then yes, your formula for error is correct.
 

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