SNOAA67A May   2021  – June 2022 TMP116 , TMP117 , TMP1826 , TMP61 , TMP63 , TMP64


  1.   Abstract
  2.   Trademarks
  3. 1RTD Introduction
    1. 1.1 Common Wiring Configurations
    2. 1.2 RTD Tolerances and Accuracy
    3. 1.3 Error Sources of RTD Systems
      1. 1.3.1 Error Minimization Circuitry
  4. 2RTD Alternatives
    1. 2.1 TMP116 and TMP117
    2. 2.2 TMP1826
    3. 2.3 TMP6x
  5. 3Conclusion
  6. 4References
  7. 5Revision History

Error Sources of RTD Systems

To convert the change in resistance of an RTD into a sensible output signal, a current source that drives a constant current through the sensing element is commonly used, thus creating a temperature dependent voltage across the RTD. This method creates two sources of measurement errors.

First, the current through the RTD causes a certain amount of self-heat that adds to the sensing elements temperature, thus falsifying the actual measurement reading. Therefore, TI recommends currents in the range of 500 μA to 1 mA maximum to minimize the impact of self-heating.

The second error source is the voltage drop across long measurement leads as is expected in PT100 applications. The voltage division between the lead resistance and the RTD can significantly reduce the measured output voltage at the signal amplifier input, yielding a false temperature reading. To minimize the impact of lead resistance, the leads must either be short when using a 2-wire RTD, or the RTD itself must accommodate lead-compensation wires, as provided in 3-wire and 4-wire RTD designs.