5. What are the differences between 2, 3 or 4 wire configurations?

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RTDs (Resistance Temperature Detectors) are offered with 2, 3, or 4 lead configuration.  The best configuration for a specific application depends on a number of factors, however the sensor configuration must match instrumentation, otherwise leadwire resistance cancelation circuitry may be ineffective.  

Factors to consider:

  • Cost of installation – more wires generally means higher cost
  • Available space – more or larger wires require more space
  • Accuracy requirements – 2 wire configurations may provide the required accuracy, especially with high resistance elements

A. 2-lead constructions result in leadwire resistance getting added to the element resistance.  Consequently, the temperature reading is artificially high. The graph below shows the temperature error, from 2 leads of various sizes and lengths, for a 100-ohm platinum RTD at 100°C.

2-lead constructions (RTD)


B. 3-lead constructions result in canceled leadwire resistance error only if the instrumentation can measure true 3-wire resistance.

  • Leadwire resistance error cancelation is most effective when all the lead wires have the same resistance. Using 3 wires of the same AWG, length, and composition will typically result in leadwire resistances matched within 5%. The graph below shows the temperature error from leadwire of various sizes and lengths, for a 3-lead 100-ohm platinum RTD at 100°C.

3-lead constructions (RTD)

C. 4-lead constructions result in canceled resistance only if the instrumentation can measure true 4-wire resistance. True 4-wire resistance measurement will effectively cancel leadwire resistance error even if all 4 wires are not the same AWG, length, and/or composition.


D. Are any configurations interchangeable?

  • 4-lead RTDs can generally be used as 3-lead RTDs by eliminating (or tying off) one of the leads
  • 4-lead RTDs can be used as 2-lead RTDs, by combining (shorting) the common leads (usually of like color – white/white and red/red)
    WARNING: combining the common leads eliminates leadwire resistance cancellation benefits
  • 3-lead RTDs can be used as 2-lead RTDs, by combining (shorting) the common leads ((usually of like color)
    WARNING: combining the common leads eliminates leadwire resistance cancellation benefits

E. See our “Resistance Thermometry” white paper for detailed analysis.

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