Red Seal Instrumentation and Control Technician Practice Exam

How does a thermocouple operate?

1. By measuring resistance change

2. By generating a voltage based on temperature difference

3. By converting thermal energy into light

4. By controlling valve positions

The correct answer is: By generating a voltage based on temperature difference

A thermocouple operates by generating a voltage that is directly related to the temperature difference between two junctions made of dissimilar metals. This principle is known as the Seebeck effect. When the two metals are joined at one end (the measuring junction) and exposed to a temperature, while the other ends (the reference junction) are kept at a constant temperature, a voltage is induced. This voltage can then be measured and is proportional to the temperature difference between the junctions. The ability of the thermocouple to produce a measurable voltage from a temperature difference makes it an effective and widely used temperature sensor in various applications, ranging from industrial processes to household appliances. The design and materials of the thermocouple can also affect its sensitivity and range, which contributes to its versatility in temperature measurement. The other options do not describe the fundamental operation of a thermocouple. Measuring resistance change is characteristic of resistance temperature detectors (RTDs), converting thermal energy into light pertains to certain types of thermal imaging or emission sensors, and controlling valve positions is related to control systems and actuators rather than temperature sensing.