Micrologix issues running PID in manual mode

Join Date
Aug 2017
Location
Wyoming
Posts
2
I'm trying to get my PID function to go into manual mode and give the CV a value through a MOV instruction. I can set the Auto/Manual bit, and the integer value (N7:2) appears to be moving into the Control Output CV, but my control variable itself (N7:1) isn't moving.

The only way I can get my control variable to move is if I go into the PID Setup screen and manually enter the value into the Control Output CV (%) data field. See pictures for reference.

Any help would be greatly appreciated!

RSLogix PID issue logic.jpg rslogix PID issue value entered into PID setup.jpg RSLogix PID issue value entered through MOV instruction.jpg
 
Control Variable Percent (CVP)
CVP (Control Variable Percent) displays the control variable as a
percentage. The range is 0 to 100%.
If the PD10:0/AM bit is off (automatic mode), CVP tracks the control
variable (CV) output being calculated by the PID equation.
If the PD10:0/AM bit is on (manual mode), CVP tracks the value that can
be manipulated in the Control Variable (CV) data word.
The only way for a programmer to have control of the PID CV is to place
the PID instruction in manual mode and write to the CV word via the

control program or programming software. If no change is made to CV
while in manual mode, the CVP will display the last value calculated by
the PID equation.
Scaled Process Variable (SPV)
The SPV (Scaled Process Variable) is the analog input variable. If scaling is
enabled, the range is the minimum scaled value (MinS) to maximum
scaled value (MaxS).
If the SPV is configured to be read in engineering units, then this
parameter corresponds to the value of the process variable in engineering
units. See Analog I/O Scaling on page 303 for more information on
scaling.
Output Parameter
Descriptions
Address Data
Format
Range Type User Program

You need to write to the CV while in manual.In your case N7:1 (0-16383) (see excert from manual above)
 
Last edited:

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