Micrologix PID

Does anyone know why my PID doesn't work? I am sure it is something simple, but I do not know what it could be. On my analog inputs, the 3276 - 16383 represents my 4 - 20 mA signal.

My 3153 - 15635 represents the actual values for a 4 - 20 mA input to the card. The 8761 represents a 9 GPM required flow. Any help would be appreciated.

thanks in advance,
Rojay

Have you called for Lad 3? From the looks of things there is nothing in Lad 2, this is the first one that the PLC will scan, if Lad 3 isn't called here then it isn't scanned.
lad 2 should contain an unconditional JSR instruction if you want to always scan Lad 3.

Looked further at your code an noticed that you also have Lad 4, this too needs to have a JSR, normally I would have all fo the JSR instruction isn Lad 2.

Welcome to the forum as well.

Thanks for replying Freak. I do have all of my JSR commands in Main2, I just deleted all of the other logic for file size considerations. At first I tried running the straight PID, with my needed 9GPM setpoint level, and had no output from my PID. So I added to to the value that represents my 9GPM, thinking that my PID would only output the needed correction factor. I was told to have my input represent my flowmeter range, but it being only a 0-20GPM transmitter, I wanted more resolution than that. I tried using a float, but the PID didn't like that. If you have any other questions that mighy help you figure out what I am doing wrong, please ask.

Hi - can you zip and attach the whole program? I'd like to see the actual PID setup screens.

Cheers

Freak, I attached the setup screen as a .DOC in the original posting, is that what you are looking for?

Rojay64:
Look at the attached file.
PV is between 0 - 16383 not between 3276 -16383, please correct both SCP instructions.
Is subroutine LAD4 called from main ??
Have you try to handle PID in manual mode, confirm that your variables behave the way they should be, i.e flow goes from min to to max when CV moves from 0 - 100 %.

Thanks everyone, I used the numbers of 3153 - 15635 because those were the actual values I got for a 4 - 20ma input signal. I was trying everything. I appreciate all of you input, and am going back out to the panel tomorrow, and do all the things people are telling me. You all seem to be on the same page, so I'm sure it will work. I will keep you posted.

if you send us the whole program it'll be better.