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from the instruments department...
PID feedback
PLCs and related questions. topic
Posted by david wiseman on 20 March, 2003 - 1:39 pm
I am trying to get two PID loops to track each other. The PLC I am using PLC 5, cannot do this. Does any PLC stub have feedback from another loop as an input. Discrete controllers do but I can't find a PLC that does.

cheers


Posted by JimU on 20 March, 2003 - 3:35 pm
Modicon has it with their PID2 instruction. This is available with ProWorx NxT software. I've used it many times and also have been confounded by its lack of availability in other PLC products.


Posted by Blunier, Mark on 21 March, 2003 - 1:48 pm
The PLC 5 can to this, but it may depend on your software. This works in frameworks.

Mark Blunier
Any opinions expressed in this message are not necessarily those of the company.


Posted by Keith Hogan on 24 March, 2003 - 4:19 pm
David Wiseman wrote, "I am trying to get two PID loops to track each other. The PLC I am using PLC 5, cannot do this. Does any PLC stub have feedback
from another loop as an input. Discrete controllers do but I can't find a PLC that does."

The Enhanced PID instruction built into the Function Block Diagram editor for Rockwell Automation's ControlLogix product has built-in support for this capability.

Keith Hogan
Rockwell Automation

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