micrologix 1400 PID

Join Date
Jan 2013
Location
california
Posts
32
First time using a PID instruction on a micrologix 1400 Platform, my issue is putting the PID instruction in manual and writing to the CV for manual operation of the loop. I set the AM bit true and should be able to use a MOV instruction to write my manual percentage to address PD#.CVP correct? From 0 to 100? I tried this and I cannot control the control variable manually, I have to set the AM bit true and write directly to the output. Also when I switch the PID instruction from manual to auto, my PID output isn't exactly smooth, is there a way to perform a bump less transition from auto to manual. This PID is for a heating temperature control loop.
 
You write to the "CV" (PD??.?.CV) when in the manual mode to control the output.
See PDFs below.

Instruction set if you need it. Chapter 20.

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1766-rm001_-en-p.pdf

To get a bumpless transfer going from manual back to auto you need to write "MOV" the PV's value to the Setpoint while in the manual mode. You may have to readjust the set point after going back the the auto mode. The actual values 0-16383 or engineering units will depend on how you set-up the "Set-Point Scaling" see manual for more info on this.
 

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