thermistances

Thermistances, or thermistances, are a class of temperature-sensitive resistors whose resistance changes with temperature. The term thermistance is often used interchangeably with thermistor, though thermistors is the more common plural in modern usage.

There are two main types. Negative Temperature Coefficient (NTC) thermistors decrease in resistance as temperature rises, making them useful for temperature sensing and compensation. Positive Temperature Coefficient (PTC) thermistors increase in resistance with temperature, and are commonly used for overcurrent protection and self-regulating heating elements.

Thermistances come in several forms, including discs, beads, chips, and film devices. They are widely used for monitoring and controlling temperatures in electronics, automotive sensors, consumer appliances, medical devices, and industrial equipment. PTC types may serve as resettable fuses in circuits.

The electrical response is nonlinear, so resistance is related to temperature through equations such as the B-parameter model or the Steinhart–Hart equation. Accurate use requires calibration and temperature range specification. To minimize self-heating, measurements are typically made with small excitation currents.

Advantages include high sensitivity to temperature changes, small size, fast response, and low cost. Limitations include nonlinear behavior over wide ranges, drift with age, tolerance variation, and vulnerability to mechanical or moisture stress. They are most effective when selected for a defined temperature range and paired with appropriate circuitry.