Modicon PID2 Function Block


Thread Starter

Brady Matherne

Hello Everyone,

I've recently been given an assignment for a PLC project that requires a PID loop being implemented to control the flow rate on a pump. In the course of the program there will be times that I want the PID2 function block to not be processed so I can maunually set the output value. My question is: does the top input to the function block, the Auto/Manual input do this, or is this input used for something else. This is my first PID implementation, and don't have the equipment in house to test with. Any help would be greatly apprecialted.

Brady Matherne
PLC Tech
Panel Specialists, Inc.

PS Keep up the good discussions, even though some of us don't post often, I've learned alot following other discussions. Thanks :)

Brian Kukulski

If you want the loop to be in manual to set the output - open the top node to the block. Also when you set the manual output be sure to put the same value (0-4095=0-100%) into the PID output register (the third register in the PID group of registers) then when you put it back to auto mode, it will beging from there as you would expect . Make sure to watch the Analog output scaling. If you are using 984-141 or compact processor using an DAU-202 card the 4-20 ma is driven by 2400-4000 into the AO reigster. The PID loop uses 0-4095 as its output range so you have to scale it manually.