4-20mA PLC out to recorder

Learn the NEC with Mike Holt now!
Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I'm struggling with the wiring between a 4-20 PLC output channel and a telemetry/data recorder. Below is a diagram of the PLC and the recorder. I guess I don't understand the nature of the PLC output and how it is supposed to create a loop with the recorder. Any help is appreciated.
I will add--if it makes a difference--that the PLC is operating at 24VDC as shown. The recorder has the ability to provide its own loop power, but at 12VDC.

PLC-RU.jpg
 
That's what I did first--just a straight + to +, - to COM. I get no reading at the recorder when I do that.
I don't have access to the PLC programming. Is there a way to check the output signal?
 
The schematics (my picture) state "4-20mA output signal for customer use", and this control panel was designed to use a level transducer for controls AND have an output for data recording.
Connected straight through, the recorder shows zero reading, and I read 0mA with a meter inserted in the output circuit.
 
I'll add that the HMI of the PLC shows and input value for the level transducer AND it shows a matching value for the output in question. So it seems that the output is programmed to be active. This makes me think there's more to the wiring of the recorder than just + and com.
 
You should be able to check real quick if the output is functioning by putting either a DMM in mA mode across 4171 and 4178, or a small, low-power resistor across those same terms and measuring the voltage across it.
 
I think I got it:
After a good bit of scrutiny, I found that the panel builder miswired from the terminal blocks (4171,4181) to the wrong channel on the analog out extension card of the PLC!
Thanks as always for the help and feedback!!
 
You must log in or register to reply here.
Top