The Thermistor

A thermistor is an electrical component in which the resistance decreases as the temperature increases.

It has the following symbol:

 

  • At low temperature the thermistor has a high resistance and little current can flow through it.

  • But at high temperatures the resistance of the thermistor is low and more current flows through it.

It is this property of the thermistor that allows it to be used as a temperature sensor. A Thermistor can be used as an electronic thermometer in which the current flowing through it at different temperatures can be calibrated in degrees Celsius to give a temperature reading. A thermistor is also used in a fire alarm. A thermistor is placed into a fire alarm circuit such that above a set temperature the current through the thermistor is at an amount to trigger a relay circuit which rings an alarm.

 

Current Potential graph for a Thermistor