RTD 4-WIRE Signal Conditioner circuit solution

Ivan Alonso

Other Parts Discussed in Thread: XTR105, ADS1263, INA821, LMP7704, ADS1262, ADS1248

Hello Guys,

I've got a very accurate PT100 (RTD) 4-Wire probe to measure temperatures in fluid, and I would like to design an adapter PCB (Analogue Front-End) in order to connect the sensor to a DAQ Card, so I need a voltage output (-10V - +10V Max) from this circuit.

The idea is to include in this circuit an accurate current source and an amplifier in order to adapt the temperature measurement.

I don't want to reinvent the wheel, so I would like to ask if TI provides any kind of solution for this?

There is a solution for RTD-3 Wires, which is the XTR105 chip. But I need to find an example for RTD-4 Wires.

Also, I am aware that there are solutions like "ADS1263", but I really need to use our DAQ Card for my system, so I need an analogic voltage as Output (Not SPI)

Thanks in advance.

KR,

Ivan

over 1 year ago

0 Michael Hartshorne over 1 year ago

TI__Genius 12245 points

Hi Ivan,

Can you check the 4-wire post in the link below and see if this fits your needs?

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1038162/analog-frontend-circuit-for-4-wire-rtd

Best Regards,
Mike

0 Ivan Alonso over 1 year ago in reply to Michael Hartshorne

Prodigy 40 points

Hi Michael,

Thanks for your reply, I saw that post before, but unfortunately, it does not fit in my system.

Raymond Zhang1 mentioned this "If you are interested in the discrete Pt100 RTD design approach, please let us know. For instance, we can use precision current source in REF200 REF102, and we have various Programmable Gain Amplifier (PGA) to support the RTD applications."

So my question is, do you have any chip to integrate only Current source + PGA ? it would be like (as I mentioned before) XTR105, but I need a solution for RTD 4-wires.

Please, let me know.

Thanks in advance.

KR,

Ivan

+1 Luis Chioye over 1 year ago in reply to Ivan Alonso

TI__Guru 53436 points

Hello Ivan,

As you have mentioned, at the input, the XTR105 is intended for a 2-wire RTD or 3-wire RTD probe/sensor. From the output perspective, the XTR105 is a two-wire current transmitter, producing a 4-20mA current output.

Unfortunately, we do not offer a PGA + Current source stand-alone solution, or a PGA device that incorporates the current sources to excite the RTD sensor in the same IC. As explained on the previous post, you could create the RTD excitation current source discretely with a reference voltage. One example for a discrete solution is on the application note below, where they use the LMP7704 amplifier in a difference amplifier configuration. You could use a similar circuit replacing the LMP7704 (configured as difference amplifier) and replace by an instrumentation amplifier such as the INA821 supporting bipolar supplies.

https://www.ti.com/lit/an/snoa481b/snoa481b.pdf

The most popular 4-wire RTD precision solutions involve highly integrated Delta-Sigma ADCs incorporating the PGA front-end, and the RTD excitation current sources in the same IC. For example, the ADS1248, ADS1262 are integrated Delta-Sigma ADCs for RTD applications. However, these solutions provide the results through a digital SPI interface.

https://www.ti.com/tool/TIPD164

https://www.ti.com/lit/ug/tidu491/tidu491.pdf

https://www.ti.com/lit/an/sbaa336a/sbaa336a.pdf

Thank you and Regards,

Luis

0 Ivan Alonso over 1 year ago in reply to Luis Chioye

Prodigy 40 points

Hi Luis,

Thanks a lot for your reply.

Yes, this info could be useful for my system. Thanks a lot !! :-)

Kr,

Ivan

0 kai klaas69 over 1 year ago

Guru 140200 points

Hi Ivan,

have you thought about using the MSC1211?

Kai

0 Luis Chioye over 1 year ago in reply to kai klaas69

TI__Guru 53436 points

HI Ivan,

Thank you, please let us know if you have questions.

Regards,

Luis

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RTD 4-WIRE Signal Conditioner circuit solution