Red Seal Instrumentation and Control Technician Practice Exam

What type of sensor uses changes in resistance to measure temperature?

1. Thermocouple

2. Infrared sensor

3. Resistance Temperature Detector (RTD)

4. Capacitance sensor

The correct answer is: Resistance Temperature Detector (RTD)

A Resistance Temperature Detector (RTD) is a type of sensor specifically designed to measure temperature through changes in electrical resistance. The operational principle of an RTD is based on the fact that the resistance of certain metals, such as platinum, changes predictably with temperature. As the temperature increases, the resistance of the RTD also increases in a nearly linear relationship, allowing for accurate temperature measurement. This property makes RTDs highly reliable for precise temperature readings in various industrial applications. In contrast, a thermocouple operates by generating a voltage based on the junction of two different metal wires at different temperatures, utilizing the Seebeck effect. Infrared sensors focus on detecting thermal radiation emitted by objects to determine temperature, while capacitance sensors measure changes in capacitance caused by changes in temperature or other factors. These other devices do not rely on resistance changes for temperature measurement, which clearly distinguishes RTDs as the correct choice for this question.