Thermistors

What is a Thermistor?

A Thermistor is a temperature sensing element comprised of a mix of metal and metal oxide semiconductor materials. Thermistors normally have negative temperature coefficients in which the thermistor’s resistance decreases as the Thermistor’s temperature increases. Hence they derive their name due to being ‘Thermal Resistors’.

Thermistors are a cost-effective alternative to sensors for measuring temperature and still work with a high degree of accuracy. They come in different shapes such as, disk, bead, rod, or chip usually encapsulated in epoxy resin, paint, glassed or phenolic and can be mounted or fixed into the system needing monitoring.

How does a Thermistor work?

A thermistor does not measure and display temperature conventionally like other temperature sensing devices, instead the resistance of a thermistor changes with temperature.

The amount of change in resistance is dependent on the detecting material used in the thermistor and the media being measured. Requiring the measurement of a solid, liquid, or gas usually dictates what the optimal material for the job is.

A temperature controller is used to monitor the temperature of the Thermistor and sends a signal to a heater or cooler to regulate the temperature of the sensor.

While the main use of Thermistors are as resistive temperature sensors, they can also be connected in series with another component or device to control an electrical current flowing through them.

Type of Thermistors

NTC (Negative Temperature Coefficient) Thermistors – NTC Thermistors decrease resistance as temperature rises. An NTC is commonly used as a temperature sensor, or in series with a circuit as an inrush current limiter.

PTC (Positive Temperature Coefficient) Thermistors – PTC Thermistors increase resistance as temperature rises. PTC thermistors are commonly installed in series with a circuit, and used as resettable fuses to protect against overcurrent conditions.