3-Wire Xmitters - Wiring Rqmts

[jgruizinga]

I've been tasked with adding a 3-wire pressure differential transmitter to a system and drawing up the wiring to an existing PLC board. The transmitter is a Veris PW Series, which is a 3-wire transmitter with a pos., neg., and signal. I'd like to set it up for 4-20mA output, but the existing drawing I have for the card I want to use only has pos. and neg. How is this generally accomplished when I have 3 conductors coming from the transmitter? I could pull power from the cabinet, but then I don't know how to send the signal to the control board.

I understand that this is probably very elementary for many of you, but any help is greatly appreciated. Thanks!

 

[Tom Jenkins]

The positive is the power supply. The negative is shared by the signal and the power. The signal is the 4-20 output.

 

[jgruizinga]

Ohhh, that makes sense. Thanks Tom!

 

[g.mccormick]

What is the full model number of the transmitter? Some of those transmitters can be used as either 3-wire voltage output or 2-wire 4-20ma.

 

[jgruizinga]

It's a Veris PWLX04S. The manual says: "Output: 3-wire transmitter; user-selectable 4-20mA/0-5V/0-10V". I didn't see anything in the manual that suggests it can be loop-powered, but I'm obviously not very experienced in instrumentation and controls.

 

[Bit_Bucket_07]

The manual says: "Output: 3-wire transmitter; user-selectable 4-20mA/0-5V/0-10V".

The phrase "3-wire transmitter" implies that the loop excitation power is provided by the transmitter.

 

[parky]

If using 3 or 4 wire transmitter then the analogue input needs to be passive (i.e. no power from the card to the transmitter ) loop powered. 2 wire is where the power is fed via the loop from the card (active).

 

[Tom Jenkins]

Here are some examples of each. You should be aware that some controller analog inputs share a single common (-) on all inputs on the I/O card.