Wiring 4-20mA splitter

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Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I have a 4-20mA level sensor wired to a pump PLC. In addition to the level signal controlling a drive, the PLC is supposed to output the signal to a telemetry/data-logging unit. That output isn't responding, and I don't have access to the PLC programming to try a different output channel. I want to install a signal splitter to get the sensor signal to the PLC and the telemetry unit, but when I went to do it, I kept confusing myself on where/how to insert the splitter into the existing loop.
Below is a sketch of how I think it should be done and a spec sheet on the splitter. Any input would be appreciated. TIA
WW splitter diagram.jpg
 

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I considered that, but there are some good length runs between the PLC, sensor, and telemetry unit. That, and the sensor being powered by only 12V has me concerned.
 
A typical 4-20 mA transmitter can drive 20 mA into a circuit with a total resistance of 750 ohms. The typical input device has a resistance of 250 ohms, leaving 250 ohms for the circuit wiring.
 
Admittedly, the runs aren't super long: maybe 100' from PLC to sensor and 50' from PLC to telemetry with 18 or 20AWG twisted pair cable.
Another reason I wanted the splitter is that the signal to the PLC to control the drive is crucial whereas the telemetry is non-crucial data collection. I'm afraid of something in the telemetry part of the loop failing and affecting the drive if I series everything together. (Of course, the splitter itself is also a point of potential failure.)
Is the splitter really that bad of an idea? Regardless, I would appreciate any help wiring it into the PLC. When I stand in front of the density of terminal blocks, I get a bit mixed up in my head.
Thanks again.
 
Yes, the signal from the sensor to the PLC is fine. There's an analog out channel of the PLC that is supposed to send that signal to the telemetry, but it is dead. As I mentioned, I don't have programming, software, etc. to alter the PLC channels.
 
I just want to bump this thread to see if anyone has input or corrections for the wiring plan in my original post.
Thanks.
 
don_resqcapt19 said:
A typical 4-20 mA transmitter can drive 20 mA into a circuit with a total resistance of 750 ohms. The typical input device has a resistance of 250 ohms, leaving 250 ohms for the circuit wiring.
Click to expand...
That's for a 24 VDC powered device. A 12 VDC device as this guy has is not going to be able to push through as much resistance as a 24 VDC device.

I don't know about typical input devices but a fair number of PLC analog inputs are 50 Ohms.
 
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