Which RTD wiring configuration provides the highest accuracy by eliminating lead resistance effects?

• A. 2-wire RTD configurations provide the simplest connection but are most affected by lead resistance.
• B. 3-wire RTD configurations reduce lead resistance error compared to 2-wire.
• C. 4-wire RTD configurations eliminate lead resistance effects entirely.
• D. RTD configurations do not affect accuracy.

Answer: (C)

In RTD measurements, the resistance of the lead wires can distort the reading because that lead resistance is in series with the sensor and can vary with length and temperature. The four‑wire (Kelvin) configuration removes this error by separating the current path from the voltage-sensing path. Two wires carry the current to the RTD, while a separate pair of wires sense the voltage directly across the RTD terminals. The measurement computes resistance from this sensed voltage divided by the current, so the lead resistances don’t contribute to the measured value. That’s why this arrangement yields the highest accuracy.

Two-wire arrangements suffer because the lead resistance adds to the RTD’s resistance, and there’s no way to separate the two in the measurement. Three-wire configurations improve things by using a third conductor to help cancel out one leg’s lead resistance, but they can still leave some error if the lead resistances aren’t matched perfectly. Four-wire eliminates lead resistance effects entirely (within practical limits), which is why it’s the best choice when precision is essential. Practical notes: higher wiring complexity and cost, but the gain in accuracy is why it’s preferred for critical measurements.