Which pair of sensors is commonly used to measure temperature?

• A. Thermocouple and RTD
• B. Orifice plate and magnetic flow meter
• C. Piezoelectric sensor
• D. Float switch

Answer: (A)

Temperature measurement in instrumentation commonly relies on two sensor families: thermocouples and RTDs. A thermocouple works on the Seebeck effect, producing a small voltage at the tip when there’s a temperature difference between the sensing junction and a reference junction. That voltage is proportional to temperature, making thermocouples simple, rugged, and capable of covering very wide temperature ranges with fast response. RTDs, on the other hand, change resistance with temperature, typically using platinum for stability and accuracy. They provide higher precision and repeatability, though they can be slower to respond and are usually more expensive. Together, they cover a broad span of temperatures and accuracy requirements found in many applications.

The other options aren’t primarily used to measure temperature: an orifice plate and a magnetic flow meter gauge how much fluid is moving, not its temperature; a piezoelectric sensor detects pressure, vibration, or force; a float switch detects liquid level.