3-Wire analogue transmitter signal splitter

mzanlongo

Member
Join Date
Jul 2014
Location
Perth
Posts
3
Hello, I have a simple 3-wire 4-20mA pressure transmitter which I would like to split into two signals to send one to the devices interface and the other to a PLC for indication in SCADA.

The problem is we have purchased a 2-wire splitter. Could I still use this splitter to split the 3-wire signal? how would I wire it?

Kind Regards,

Signal Splitter:
https://eshop.wago.com/JPBC/0_5Star...4?supplierAID=857-423&catalogID=WAGO01&zone=7

Dont have the name of the transmitter, but its a typical 3-wire analogue 4-20mA
 
The third wire just provides power to the transmitter and isn't part of the output signal. You can wire the two output wires the way you would any 4-20 output, with the same cautions about total loop resistance, ground loops, etc. as any 4-20 loop.
 
Or you could take it back and swap for this Wago 2-wire signal splitter, 2 IN, 2 OUT. Run your 1 Input to both the left-side IN terminals.

https://eshop.wago.com/JPBC/0_5StartPage.jsp?TopNavi=0_6TopNavi.jsp&Zone=2&Hauptframe=%2FJPBC%2FCommonPageHandler.jsp&activatedPage=SEARCHPAGE

I did think of that option, but if one of the 2 instruments were to stop, both would lose the signal.
No, it is a current loop (complete circuit) and as long as the the driven loop signal is present, it still gets passed though the dead reading device. The signal is lost only if the loop is broken at some point.
 
Last edited:
I seem to be a bit confused on the 3-wire transmitter. The first wire would be the 24VDC power, the second the signal and the third the ground. Would the signal wire have a voltage of 24VDC on it also?

Also, the splitter requires a 24Vdc power source as it's used to power the 2-wire transmitter. If I connect the signal wire from the 3-wire transmitter into the IN of the splitter, the splitter would be injecting 24V. Would this affect the signal??
 
1) The voltage level in the signal wire will vary with both the total resistance of the loop and the signal current. Ohm's Law is the defining equation.

2) The splitter doesn't inject voltage it re-transmits the current signal

3) Draw a loop diagram, with little arrows showing the current direction in each and every wire. Note which devices are energy sources (power supply for example), which are energy consumption (PLC input for example) and energy conversion (the transmitter for example). That should help you understand what each component does and how the current and voltage changes. Remember Kirkhoff's Law and the First Law of Thermodynamics.
 
I believe this is what you are trying to do? Not sure what WAGO model you have, the link is not working for me. I used the JUMPFLEX® transducer; signal splitter; with 2 configurable current outputs.

Signal Splitter.jpg
 

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