Signals and sensors

RTD lead-resistance error estimator

Estimate the temperature error contributed by two-wire lead resistance or three-wire lead mismatch at a stated RTD sensitivity.

Calculate

Lead model
Ω
Ω
Magnitude only: the circuit determines whether the indicated temperature shifts high or low.
Ω/°C

Worked example

Lead-resistance error, magnitude

 °C

Uncompensated resistance in the model
0.1 Ω
Ideal lead compensation
Only equal lead resistances cancel

Three-wire mismatch is shown as a magnitude; which lead is higher determines whether the reading shifts high or low. Add other uncertainty separately.

Underlined figures are rounded. Select one to copy its full value.

Method and assumptions

Formula

2-wire error ≈ 2Rlead ÷ sensitivity; 3-wire residual ≈ lead mismatch ÷ sensitivity; ideal 4-wire lead error ≈ 0

This is a local linear estimate around the entered operating point; use the actual sensitivity of the RTD curve there.

Limits of this result

  • Three-wire cancellation assumes the relevant lead resistances are equal; the entered mismatch is the uncompensated difference.
  • Four-wire selection removes ideal lead resistance from this estimate, not instrument offset, leakage or thermoelectric effects.
  • Add sensor tolerance, transmitter accuracy, self-heating and thermal-installation errors separately.

Technical sources

  1. RTD measurement system design essentialsAnalog Devices · technical article, 2016-06-15
  2. IEC 60751 industrial platinum resistance thermometersIEC · IEC 60751:2022 catalogue record

Put the value to work

Read the related engineering guidance, or carry this task into System Builder to identify the signal path and EpiSensor products.

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