View Full Version : PID control using plc

February 9th, 2011, 10:48 PM
hi,friends i tried to study pid control using PLC for that purpose i have used rslogix 500 and select ML1400 as plc.after making the ladder logic.i have downloaded the program to rs emulate 500 and tried to simulate the control but i found that PID dosen't producing any control signal.i have tried different values for SP,PV..but still PID controller not producing any cv out put.At the same time i am able to produce produce CV out put by changing the mode to manual and by increasing %cv.
Is this mean that RSemulate is not able to provide the stimulation for PID controller.And For that we need Actual hardware?
i tried the same thing by using scaled and non scaled raw data for pv and sp but still PID not producing any cv Out put.
i have also change loop update time to several value but still no cv out put .
so can any body tell what i should do to solve the problem?

Peter Nachtwey
February 9th, 2011, 10:57 PM
It is in the download section misc/hotrod.zip.

February 11th, 2011, 12:38 AM
i have download hotrod.zip...and load the same program in my pc with emulator as drive but still my CV out put is not changing with change in PV,other thing is that in the PID block PV is always showing Value zero even though i am changing N7:0 which i have assigned for process value in PID block...

February 11th, 2011, 07:34 AM
Two ideas come to mind.

1. Do a Find All for N7:0. You may be overwriting it somewhere else in your program

2. If your PID block is in a sub routine (I.e. Not in Lad 2) then you may not have a JSR instruction to call the subroutine.

February 11th, 2011, 11:23 PM

hi ndzied1,There is no problem with N7:0 and PID block is in the lad 2 but still its not working ,i just want to know whether the rsemulateor is capable of handling PID instruction or not (http://www.plctalk.net/qanda/member.php?u=928)

Ken Roach
February 11th, 2011, 11:30 PM
That's because RSEmulate 500 doesn't support the PID instruction.

The Emulator doesn't have a precise clock, and the PID instruction requires one, so they simply don't execute that instruction. There are quite a few instructions that depend on the hardware and are not executed by the Emulator; they are listed in the Knowledgebase (http://rockwellautomation.custhelp.com/app/answers/detail/a_id/55723).

Peter Nachtwey
February 12th, 2011, 12:09 AM
A real PLC is required but the system that is being controlled is simulated. The system is modeled on Ron Beaufort's hotrod systems.