How do you configure a PT100 RTD in a three-wire arrangement to minimize lead resistance errors?

How do you configure a PT100 RTD in a three-wire arrangement to minimize lead resistance errors?

• A. Use a three-wire connection with compensation; measure across two wires and adjust offset to cancel lead resistance
• B. Use a two-wire connection and accept lead resistance
• C. Use a four-wire arrangement but ignore compensation
• D. Use a single wire configuration

Answer: (A)

Lead resistance from the wires can skew an RTD reading because the current path includes the wire resistances in addition to the sensor element. In a PT100 wired with three leads, two wires carry the measurement current and the third acts as a sense line to gauge the resistance of the lead wires themselves. The instrumentation uses this sense information to apply compensation, effectively subtracting the lead resistance from the total measured resistance. This offset adjustment cancels the influence of the wire resistances, so the reading reflects only the RTD element’s resistance and, therefore, the true temperature. Two-wire setups suffer from lead resistance added to the RTD, giving less accurate results. A four-wire arrangement can eliminate lead resistance more cleanly, but when limited to three wires, using the compensation approach with a sensing lead provides the best reduction of lead resistance error.

Lead resistance from the wires can skew an RTD reading because the current path includes the wire resistances in addition to the sensor element. In a PT100 wired with three leads, two wires carry the measurement current and the third acts as a sense line to gauge the resistance of the lead wires themselves. The instrumentation uses this sense information to apply compensation, effectively subtracting the lead resistance from the total measured resistance. This offset adjustment cancels the influence of the wire resistances, so the reading reflects only the RTD element’s resistance and, therefore, the true temperature.

Two-wire setups suffer from lead resistance added to the RTD, giving less accurate results. A four-wire arrangement can eliminate lead resistance more cleanly, but when limited to three wires, using the compensation approach with a sensing lead provides the best reduction of lead resistance error.