Reply To: PID output percent start at zero

#3766
Soolocks5779George Barnette
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Thanks for the reply. OK so I may not need to write anything to .SO. I will only write to .OUT and then the percent out for the CV. I made a few changes while I was waiting for some replies:

1) I put the PID on a free running rung with the only condition being the .DN bit from the update timer.

2) When I no longer want any output, I run a timer for about 7 seconds that moves a low setpoint into the PID.SP, much lower than the PV, and since it is a heat PID, then it wants to ramp down, then I move a 2.0 gain into the PID.KP so it will go to zero output really quick; all this from that timer .TT bit. and then a zero into the output %. This seems to be doing OK now, and when it calls for heat again (the burner enable bit enables this timer along with other things), then a higher setpoint gets written back in and the loop returns to normal. I’ve watched it and the setpoint is re-entered higher than the PV and so the PID starts out SLOWLY from zero like I want it. May be a little clunky, but it works. I use a temp setpoint sequencing routine that raises and lowers the setpoints automatically based on a certain temp. Those are from the supply air that is heated by the burner. Thanks for all your help, and if you can think of anything else that would help me, I appreciate it

Respectfully

George