Which RTD connection method provides the highest accuracy?
A. 2-wire
B. 3-wire
C. 4-wire
D. Single-wire
View Answer
Correct Answer: C
Explanation:
The 4-wire RTD connection provides the highest measurement accuracy because it completely eliminates the effect of lead wire resistance.
In an RTD measurement system, the resistance of the connecting wires can introduce errors, especially when long cables are used. The 4-wire method uses separate wires for current excitation and voltage measurement, allowing the measuring instrument to accurately determine only the RTD resistance.
Comparison of RTD Wiring Methods
2-wire RTD
- Simplest connection
- Lowest cost
- Lead wire resistance adds directly to the measured resistance
- Lowest accuracy
3-wire RTD
- Most common industrial method
- Compensates for lead resistance assuming equal wire resistance
- Good balance between accuracy and cost
4-wire RTD
- Highest accuracy
- Completely removes lead wire resistance errors
- Preferred for calibration laboratories and critical measurements
The measured RTD resistance is converted to temperature using equations such as the Callendar-Van Dusen equation, ensuring highly accurate temperature measurement.
For critical applications where maximum precision is required, the 4-wire RTD connection is the preferred choice.
Therefore, Option C (4-wire) is the correct answer.