How does a thermistor function?

A thermistor is a type of temperature sensor that operates based on the principle of the temperature-dependent resistance of certain materials. Here’s how it functions:

Temperature Sensitivity: Thermistors are made from semiconductor materials that exhibit a high degree of temperature sensitivity. Their electrical resistance changes significantly with variations in temperature.

Negative Temperature Coefficient (NTC) Thermistors: The most common type of thermistor is the NTC thermistor, where the resistance decreases as the temperature increases. This characteristic makes NTC thermistors suitable for temperature measurement applications.

Resistance-Temperature Relationship: The relationship between the resistance (R) of a thermistor and the temperature (T) is typically described by the Steinhart-Hart equation or simplified approximations. As the temperature changes, the resistance of the thermistor varies accordingly.

Measurement Circuit: In a typical thermistor measurement circuit, the thermistor is connected in series or parallel with a known reference resistor (often called a “bias resistor” or “pull-up resistor”) across a voltage source. The voltage across the thermistor or the voltage drop across the bias resistor is measured.

Voltage Divider Principle: When the thermistor is subjected to a temperature change, its resistance alters, causing changes in the voltage drop across it or the bias resistor. By measuring this voltage, the temperature can be determined using calibration curves or tables specific to the thermistor’s characteristics.

Signal Conditioning: Depending on the application, signal conditioning circuits may be used to amplify, filter, linearize, or compensate for nonlinearity in the thermistor’s resistance-temperature relationship.