Allen Bradley PID

I need to control a steam valve 4-20mA output via a PID loop. I have a 4-20mA input from a temp transmitter.
I am using RSLogix and a 5/03 processor. Any ideas I have not used a PID loop before.

Peter

this topic has been dealt with on this forum many times before, possibly not specific to an AB plc, but I am sure that if you search this forum with the keyword PID you will find lots of threads that may answer your question

Paul

First question: How dangerous is this system you're working on? In other words, if things get out of hand, is someone likely to get hurt? Or are we just going to let off a little extra steam?

Second question: How familiar are you with the SLC-5/03 analog signals? For example: Is your input scaled from 3277 to 16384? Is the output signal scaled 6242 to 31208? If not, how are they scaled?

Third question: Is your system already far enough along so that:

1. you can monitor the input signal in your SLC? and

2. you can manually control the output by entering values into the output address?

Basically, you've got to have good inputs and outputs before you try for automatic control.

Fourth question: What is your deadline on this project? "As soon as possible" is NOT a valid answer.

Fifth question: Does your version of RSLogix500 have the Trends (graphing) feature available?

Sixth question: What is the HMI like?

A) Where are the setpoints coming from (Recipe, Operator, set-and-never changed)?

B) How much operator control will you be giving over the PID output. Auto/Man setting of CV? Auto/Man changing of Setpoints?

All of these things (can) factor into how you program the PID block. It's a bit more than just SOR PID N10:0 N10:23 N10:24 EOR.

Seventh question:

Is it a relief valve or an injection valve?

Peter, you would do well to post the answers to the above questions, as this can generate a lot more help for you.

Fundamentally, PID loops are simply one of the many ways used to minimize the difference between a desired value (say a temperature setpoint) and the measured value (actual temperature) by manipulating an output (like % open of a valve). It was originally developed using pneumatic devices, linkages etc. but now it is primarily used as a mathematical expression inside a microprocessor (like the PLC).

The Allen Bradley SLC Reference manual actually has a fair explanation of how PID works. One of the best explanations I've seen is in the AutomationDirect.com manual for the 250 PLC. I think you can download this from their site.

RELATED?

HELLO, MY SURNAME IS HONEY-JONES ALSO, I WAS WONDERING WHICH SIDE ARE YOU RELATED TO? COULD YOU EMAIL ME AT [email protected]