2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

RE: 2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

user4864313 — Sat, 18 Mar 2017 06:55:51 GMT

Hi Collin, I want to use TIPD126 design but ı don't understand where ı use to zero and span trim.

RE: 2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

Collin Wells — Tue, 10 Mar 2015 16:59:28 GMT

Hi Patrick,

I suppose, but you're very likely to experience grounding or other issues because the XTR devices were not intended for use in this manner. Also, what you're describing sounds like a 4-wire transmitter which typically has separate supplies for the sensor/conditioning circuitry and transmitter. The design of these systems is less common but I plan to cover them in some future blogs as well.

RE: 2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

Patrick Dussud — Mon, 09 Mar 2015 22:38:25 GMT

If the 24V supply is on the transmitter side, there is only 2 wires in the loop, isn't it?

RE: 2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

Collin Wells — Mon, 09 Mar 2015 16:53:01 GMT

Hello Patrick,

While in theory an idea like that may work, the actual implementation would violate the standards for 2-wire 4-20mA transmitters which require only two wires (Vloop, RTN) in the loop. Take a look at Part 4 which talks about a similar application concern when connecting externally powered sensors to the inputs of a 2-wire transmitter.

RE: 2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

Patrick Dussud — Sun, 08 Mar 2015 19:28:46 GMT

Is it possible to use this IC with 2 isolated supply?For example One supply of 24V between V+ and Iret and the one Vloop of 12V. the collector of the external transistor would be connected to Vloop instead of V+. The idea is that if Vloop isn't providing enough voltage for compliance (V+-IO > 7.5V), the IC could be powered by another isolated supply. Would that work?

Thanks,

Patrick.

RE: 2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

Collin Wells — Tue, 11 Nov 2014 15:05:49 GMT

Hi Ed,

TI does not offer any loop-powered 4-20mA receiver integrated circuits. The RCV420 is an externally powered 4-20mA receiver.

RE: 2-Wire 4-20 mA Sensor Transmitters: Background and Compliance Voltage (Part 1)

Ed OReilly — Tue, 11 Nov 2014 13:30:28 GMT

What IC packages does TI offer for loop powered 4-20ma "Receivers"? I've seen older designs using LM10 's that could be powered off a 4-20ma to drive a 5-32V SCR.