328 Rockwell Automation Publication 2080-UM002K-EN-E - March 2019
Appendix F PID Function Blocks
PID Code Sample
The illustration PID Code Sample shows sample code for controlling the PID
application example shown before. Developed using Function Block Diagrams, it
consists of a pre-defined function block, IPIDCONTROLLER, and four use-
defined function blocks. These four are:
• PID_OutputRegulator
This user-defined function block regulates the output of
IPIDCONTROLLER within a safe range to ensure that there is no
damage to the hardware used in the process.
IF RMIN ≤ RIN ≤ RMAX, then ROUT = RIN,
IF RIN < RMIN, then ROUT = RMIN,
IF RIN > RMAX, then ROUT = RMAX.
• PID_Feedback
This user defined function block acts as a multiplexer.
IF "FB_RST" is false, FB_OUT=FB_IN;
If "FB_RST" is true, then FB_OUT=FB_PREVAL.
• PID_PWM
This user defined function block provides a PWM function, converting a
real value to a time related ON/OFF output.
• SIM_WATERLVL
This user defined function block simulates the process depicted in the
application example shown before.
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