A-Series PLC A1SCPU24-R2 PID Control

[shortcircuit 0]

I am taking over support of a system installed by another provider. I'm new to Mitsubishi, but have been able to pick up most things pretty quickly. I am using an A Series PLC, CPU Model is A1SCPU24-R2. The customer says that once upon a time there was PID control of a valve to control pressure in a process. The PLC here does have an anlaogue output card, but the code only contains a hard-coded value for this output- no modulating control. I have searched high and low through the Mitsubishi documentation (GX Developer Operation Manual, A-Q Series Programming Guide, among others) to see if this CPU is capable of PID control, but with no success. The "Instruction Help" dialog in GX Developer has no entries under PID for this program. Any help greatly appreciated!

[andybr 5]

PID Control was possible with an A1s PLC but it was not easy. In fact by modern standards it would be considered ridiculously difficult. The An and Ans processors did not have a PID instruction which could be used within a ladder or instruction list programme. PID control could only be performed using what Mitsubishi called a Microcomputer programme. This had to be written in 8086 assembler, using Debug in DOS or something similar, and called as a subroutine from the main PLC programme. I have looked for an example or some documentation but I am afraid I no longer have anything. Mitsubishi used to sell Micro's for specific applications and I believe that one of these was for PID but I do not know whether you would be able to get hold of a copy now. If you could get it I suspect you will need an older software package than GX developer to download it to the PLC. In any case I would not recommend following this path. Using Micro's was never easy and I doubt that you will be able to find much help with it nowadays.

[Duffanator 1]

You're better off getting an outside PID controller to control the valve and just feed it an analog input via the analog PLC output. One company tried doing PID loops with an A-series controller here on one of our automated smokehouses and it was a disaster. The newer style PLC's are much better at it if you are thinking of upgrading the PLC. Use a Q-series and you won't have any problems with it.