Thread Starter


I have used the PID instruction in the SLC-500 /03 processor with success at my normal job. I am at present enrolled in community college and working with a PLC 5/10 and building a Wonderware interface to the process simulator. My task is to program 1 PID loop that has the gains and setpoint accessible via Wonderware interface. Here's the problem. In the SLC I can address the PV and control output words directly in the instruction. After playing with the PLC5 I learned I needed to use BLOCK TRANSFERS for the analog I/O, which I have done in a subroutine file. The PID resides in a 3rd file; the instruction references the integer files associated with analog input set up in the block transfer, as does the control output. When the rung is enabled the input will vary but the control output does nothing. I don’t have any documentation on the PID instruction other than the online help file in RSLOGIX5. Any help would be appreciated. I have class again this Saturday.

Thanks in advance.

Hi tjmurf,

Have you got the PID instruction set up to only come true periodically (it's like a file instruction in that way)? The time interval you chose must also be entered in the PID configuration screen under "Update Time" (in seconds). The way I normally handle this, is to put the PID rung into an STI file and "unlatch" the PID instruction. It's also handy to place all the analog variables into an integer file in a little table. That way you can see quickly what's going on.


Troy Stearns

Since you are using the SLC500 PID as your frame of reference, you should be aware that the PLC5 PID algorithm apparently is not the same as the
SLC500's. Entering the same parameters in each does not result with the same behavior and responses.

Troy Stearns

Mark Fairbaugh

There are so many things that it can be.

Check the PD instruction and make sure the PID is not in software manual


Also monitor


to verify that the output is not changing


Mark Fairbaugh
PT Newmont Nusa Tenggara
Sr. Process Control Engineer
e-mail: [email protected]
Phone: (62)-370-636-318 Ext. 47948
Mobile: (62)-812-382-0235

Dave Ferguson

There is a lot more to setting it up than that. For instance, your controller (wonderware) needs to access the PID and "put" the controller in
auto. It may be sitting in manual. You need to set the loop update time in the instruction to match "roughly" your expected scan time.

I believe it is chapter 14 in the PLC book explains this better. Your school SHOULD have one but if not they it is on the web at ab.com. You want the instruction set reference, 6200-6.4.11 I believe.

Dave Ferguson

Blandin Paper Company
DAVCO Automation