SLC PID help

[Conor 4]

Hi guys, I was wondering where I should look for this problem that I have. I have attached a screen dump from a PID. Can someone tell me why there is no Output? Thanks, Conor slc_pid.bmp

[JohnM 1]

First step would be to set Output Max to something higher than 0%.

[Conor 4]

Typical, didn't see that. I was troubleshooting this problem today and will take a look again tomorrow

[Mickey 71]

Post the whole program if you can, its .RSS file. You also have the control mode set for direct/forward acting. The process varible would have to be greater then the setpoint for the output(CV) to increase. Is that what you want? See picture below Edited 4 Feb 2014 by Mickey

[Conor 4]

Hi Mickey, I am not sure if I am allowed post directly to the forum because of IP. It is a program from a vendor that we don't have any contact with now. I checked this morning and have attached another screendump from code. Output is now set? Conorslc_pid_1.bmp

[Mickey 71]

The way you have your PID set up ( direct Acting) the CV (output) will eventually go to zero as long as the process variable (PV) is lower then the setpoint. Are you sure you don't want reverse acting ( E=SP-PV). Also as JohnM said I would enable the output limit CV and set the min/max to 0-100, this will help the PID from winding up/down to much ( anti-windup) Edited 5 Feb 2014 by Mickey