TimD
Lifetime Supporting Member
Hello, I'm confused today. I have a pump controller that has it's own 24vdc supply and takes a 4-20ma input from a level sensor to drive a pump.
I have a PLC that I want to read the same level sensor into for logging, trending and other business.
I have this set up as an analog input reading into the PLC, and analog output from same PLC to the pump controller.
So, My expected output is working, some level gives me expected milliamp output, great. Input of course works like a charm, all seems well.
I hook the AO into the pump controller, it reads a near-constant 'level', much different than what I am expecting, no matter what I do to the AO's 'percieved milliamp output' it seems the pump controller is altering the signal.
I hook up my loop calibrator into the pump controller and viola! Exactly what I'm expecting...
SO, I make the PLC generate 15ma and loop calibrator do the same. The pump controller 'likes' my loop calibrator and 'hates' my AO from the PLC...
My question is WHY are these so different? Does the loop calibrator have some resistance immunity that the AO card dosen't have? Is the AO signal being overwhelmed by the 24VDC from the pump controller whereas the calibrator is not?
I'm stumped today. Any help greatly appreciated. This has been a tough time getting one simple 4-20ma loop circuit to work between both devices. Splitting (the old-fashioned trick) never worked either.
Thanks All!!!!
EDIT: MicroLogix 1400 PLC, Standard AB Analog I/O modules, Logix 500, Alltek Calibrator, Grundfos CU-300 pump controller
I have a PLC that I want to read the same level sensor into for logging, trending and other business.
I have this set up as an analog input reading into the PLC, and analog output from same PLC to the pump controller.
So, My expected output is working, some level gives me expected milliamp output, great. Input of course works like a charm, all seems well.
I hook the AO into the pump controller, it reads a near-constant 'level', much different than what I am expecting, no matter what I do to the AO's 'percieved milliamp output' it seems the pump controller is altering the signal.
I hook up my loop calibrator into the pump controller and viola! Exactly what I'm expecting...
SO, I make the PLC generate 15ma and loop calibrator do the same. The pump controller 'likes' my loop calibrator and 'hates' my AO from the PLC...
My question is WHY are these so different? Does the loop calibrator have some resistance immunity that the AO card dosen't have? Is the AO signal being overwhelmed by the 24VDC from the pump controller whereas the calibrator is not?
I'm stumped today. Any help greatly appreciated. This has been a tough time getting one simple 4-20ma loop circuit to work between both devices. Splitting (the old-fashioned trick) never worked either.
Thanks All!!!!
EDIT: MicroLogix 1400 PLC, Standard AB Analog I/O modules, Logix 500, Alltek Calibrator, Grundfos CU-300 pump controller
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