Which of the following is used to measure temperature in power engineering?

In power engineering, temperature measurement is critical for monitoring the performance and safety of equipment. The thermocouple is a widely used device for this purpose due to its ability to provide accurate and rapid temperature readings. A thermocouple consists of two different metal wires joined together at one end. When the joined end, or the "hot junction," is exposed to temperature changes, it produces a voltage that correlates with the temperature difference between the hot junction and the other end, known as the "cold junction." This capability allows thermocouples to measure high temperatures and rapid changes effectively, making them suitable for various applications within power plants and industrial processes.

The thermocouple's versatility, durability, and relatively low cost further enhance its widespread use in temperature measurement compared to other methods. While devices like the Bourdon Tube measure pressure, and transducers can vary widely in function, especially in converting one form of energy to another, they do not specifically serve the purpose of temperature measurement. Closed loop systems are more about the control strategy and operational feedback, rather than being direct temperature-measuring devices. Therefore, the thermocouple is the best choice for accurately measuring temperature in power engineering contexts.