RTD readout using two wires

[engr_joni_ee]

Hi, I have seen typical four wire readout topology in which two wires are used as source the constant current like 1 mA to PT1000 and the other two wires for sense that can be read by microcontroller ADC.

I am wondering does it make any sense to use the same two wires that source the constant current to read by Microcontroller ADC ?

 

[barry]

Don’t know what you mean by “use the same two wires that source the constant current to read by Microcontroller ADC” but you can connect the current source terminal and top sense terminal together, and the current return terminal and bottom sense terminal together. This essentially makes it a 2-wire PRT.

The two current terminals are electrically the same as the two sense terminals as far as the PRT is concerned.

 

[engr_joni_ee]

Yes, I mean "connect the current source terminal and top sense terminal together, and the current return terminal and bottom sense terminal together. This essentially makes it a 2-wire." How this effect the accuracy of temperature readings ? If I use LM134 to provide 1 mA current to PT1000 ?

 

[FvM]

2-wire Pt1000 interface involves a temperature error caused by the wire resistance. Other than with Pt100, the error is sufficiently small for cable length up to 5 or 10 m and reasonable wire gauge. Calculate yourself.