Which component is commonly used as the temperature sensor in electronic thermostats?

Which component is commonly used as the temperature sensor in electronic thermostats?

• A. A heater element
• B. A mercury switch
• C. A thermistor
• D. A capacitor

Answer: (C)

Temperature sensing in electronic thermostats relies on a device whose electrical property changes with temperature. A thermistor fits that role because it is a small, inexpensive resistor whose resistance changes noticeably as temperature shifts—typically decreasing as temperature rises in the common NTC type used in home thermostats. The control circuit reads this changing resistance (often via a voltage divider and an ADC) and converts it into a temperature measurement. This setup offers good sensitivity in the typical room-temperature range, fast response, and low cost, which is why it’s the standard sensor in most electronic thermostats. The heater element is used to generate heat, not measure it. A mercury switch is a mechanical switch that changes state with temperature (or orientation) but doesn’t provide a continuous temperature reading. A capacitor stores charge and isn’t used as a practical temperature sensor in this context.

Temperature sensing in electronic thermostats relies on a device whose electrical property changes with temperature. A thermistor fits that role because it is a small, inexpensive resistor whose resistance changes noticeably as temperature shifts—typically decreasing as temperature rises in the common NTC type used in home thermostats. The control circuit reads this changing resistance (often via a voltage divider and an ADC) and converts it into a temperature measurement. This setup offers good sensitivity in the typical room-temperature range, fast response, and low cost, which is why it’s the standard sensor in most electronic thermostats.

The heater element is used to generate heat, not measure it. A mercury switch is a mechanical switch that changes state with temperature (or orientation) but doesn’t provide a continuous temperature reading. A capacitor stores charge and isn’t used as a practical temperature sensor in this context.