[SOLVED] 3 wire 4-20mA Transmitter

[toognitti]

This question is regarding 3-wire 4-20mA current loop transmitting
I have purchased 2 ICs from TI; the XTR 110 and XTR 111
neither of them could transmit the signals i wanted when connected according to the circuits provided in the datasheets.
I researched a bit and found that unlike a 2-wire transmission which is powered from the loop,
the 3 - wire need an external source for the supply voltage, i.e it cannot be powered directly from the loop.
So my question is; is it possible to transmit a 4-20mA signal using 3 wires without using an external voltage source as a supply?
and furthermore is this possible using the XTR 110 or 111?

 

[FvM]

The difference between two-wire and three-wire transmitter is that with the three-wire transmitter, some current is flowing through additional terminals, in case of XTR110/111 an additional ground terminal. The device isn't designed to be operated in two-wire mode, although it would be possible with an additional amplifier circuit, I guess. But you would normally refer to a different XTRxxx chip in this case.

The XTR110/111 can be operated with a two-wire input circuit if it has a grounded current shunt and you have access to the ground node additionally. I believe it's possible with most PLC input modules, e.g. it would work with Simatic S7 analog inputs. The XTR110/111 ground current is small according to datasheet, e.g. 0.5 mA.

 

[ahsan_i_h]

In two wire transmitter loop, you need to use 4-20mA two wire transmitter IC like XTR101.
Datasheet link: https://www.ti.com/lit/ds/symlink/xtr101.pdf

If you want to use XTR110/111, you need to modify the two wire transmitter loop into three wire transmitter loop by adding an extra wire connected one end to the ground node of the PLC input side (already explained in post #2). See the picture below.