PXI-2722 3 Wire RTD

[KevinBlankenheim]

I am trying to configure my PXI-2722 Resistor Module to act like a 3-Wire RTD Sensor.

I am using Channel 0, with these Relay Positions: b0shunt = Closed, b0 = Open, bc01 = Closed, b1shunt = Open, and b1 = Closed. See attachment.

My LabVIEW program can change the resistance across Pins 2 and 20 which is what I expect.

My problem is I have an Open Circuit (infinite resistance) between Pins 2 and 1.  So my solution will not act like a 3-Wire RTD.  What am I doing wrong and how can I act like a 3-Wire RTD using PXI-2722?

[Henrik_Volkers]

Have a look at the spec...  pretty high uncertainties  (1% to 10%! depending on range) and 0.25Ohm resolution.

Assuming a Pt(100 or 1000 or ..) :  1K change is less than a 0.4% resistor value change.

Well it migth work with NTCs ... and individual calibration ..   depending on the accuracy needed..

3 wire is not needed 😄

[KevinBlankenheim]

Henrik Volkers,  Thanks for taking the time to reply, but I don't understand what your point is?

I am wondering why when I Close Relay b0shunt, that Pin 20 and Pin 1 are not shorted (low resistance).  I measure an Open (high resistance) between pin 20 and pin 1.

[Henrik_Volkers]

Sorry, I mixed up a source with a RTD measurement device 🙂

[KevinBlankenheim · Accepted solution]

I have my 3-Wire RTD Simulator working. I setup the relays to connect to the external connector pins that I require, before calling ni272x Write Resistance. I removed all references in ni272x Address Bank Relay so they only change the Resistor Relays and never change the shunt or bypass Relays. I changed my Requested Resistance and used Front Panel to monitor Relay Positions and measure the Resistance at the External Connector.