Which statement best describes a three-wire RTD approach to reduce lead errors?

Which statement best describes a three-wire RTD approach to reduce lead errors?

• A. The three-wire method includes compensation to cancel lead resistance
• B. It uses four wires by default
• C. It ignores lead resistance
• D. It is only used for calibration, not measurement

Answer: (A)

The three-wire approach reduces lead errors by using an extra wire to sense the resistance of the leads and cancel that contribution in the measurement. In this setup, two wires carry the excitation current through the RTD, while the third wire provides a sensing path to determine the RTD voltage at the device end. The measurement circuitry uses this arrangement to subtract the voltage drops that occur in the leads, so the calculated RTD resistance reflects the sensor element itself rather than the lead resistances. This compensation is especially effective when the lead resistances are similar, and it provides accurate readings without needing a fourth wire, unlike the four-wire method. This technique is used for actual measurement, not just calibration.

The three-wire approach reduces lead errors by using an extra wire to sense the resistance of the leads and cancel that contribution in the measurement. In this setup, two wires carry the excitation current through the RTD, while the third wire provides a sensing path to determine the RTD voltage at the device end. The measurement circuitry uses this arrangement to subtract the voltage drops that occur in the leads, so the calculated RTD resistance reflects the sensor element itself rather than the lead resistances. This compensation is especially effective when the lead resistances are similar, and it provides accurate readings without needing a fourth wire, unlike the four-wire method. This technique is used for actual measurement, not just calibration.