Plc5/40 Pid

I have searched this site plus the AB site and could not find an answer to this question.

With a PID instruction what does SO equate to? I am familiar with PV SP CV but not SO. (as in PD20:1 SO)

As always thanks in advance.

.SO is the 'Set Output' value.

I generally use it (as I don't use tieback) when I put a PID in .SWM (Software manual) mode, and force the PID CV to a zero-effect output. It is a direct write to the output CV, as opposed to the tieback which is a bumpless transition from manual to auto modes.

You can find the PLC5 Instruction Set Reference Manual Here

Thanks Alaric. I have read the instruction and it only confused me more.

Thanks rdrast. I guess I don't understand what software manual is. The instruction states that the number you put in .SO
is used in place of the algorithm for setting the CV. This I can understand if you are in software manual but in my usage it is part of the algorithm calculating the number to put in the SP of the PID. This is confusing, why would you use a ficticious number (.SO) to calculate the setpoint of a PID when the PID is in auto.

I'll go back and reread the instruction but if you could give me a real world explaination I would appreciate it.

Thanks again

Are you saying that someone is using the output of the PID loop as a part of it's input? When in auto, .SO is .CV (essentially, there are some slight differences, one being that .SO is unaffected by the CV Limit clamps).

Perhaps somebody was trying to come up with a creative way of introducing a derivative term based on CV?