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ADS124S08: Three-wire PT100 RTD Application Consult

Part Number: ADS124S08

Hi Team,

Customer wants to consult how to use 1pcs ADS124S08 achieve 4 channel of 3-wire RTD measurement ? I see below link application ADS124S08 3-Wire PT100 RTD Measurement Circuit w/ Low-Side Reference and 1 IDAC (Rev. B) (ti.com), which seems cannot achieve 4 channel 3-wire RTD. Do you have any reference guide for us to achieve above demand?

Best,

Stanley

  • Hi Stanley,

    The circuit you provided is a 3-wire RTD measurement using a single IDAC while subtracting the lead resistance with a second measurement.  It is possible to adapt this circuit slightly where the lead resistance measurement is measured to a single point.  A colleague has put a diagram together to illustrate.

    The lead resistance measurement for RTD1 is AIN1 to AINCOM, for RTD2 AIN3 to AINCOM, and so on.

    There is also an alternative 3-wire RTD measurement using two IDACs to automatically cancel the lead resistance as given in A Basic Guide to RTD Measurements.  Unfortunately due to the number of analog inputs required the circuit requires an external mux as illustrated below for four, 3-wire RTDs.

    So there are a couple of options for making four, 3-wire RTD measurements using the ADS124S08.

    Best regards,

    Bob B