Thermistors are inexpensive, easily-obtainable temperature sensors. They are easy to use and adaptable. Circuits with thermistors can have reasonable output voltages - not the millivolt outputs thermocouples have. Because of these qualities, thermistors are widely used for simple temperature measurements. They're not used for high temperatures, but in the temperature ranges where they work, they are widely used.
Thermistors are temperature sensitive resistors. All resistors vary with temperature, but thermistors are constructed of semiconductor material with a resistivity that is especially sensitive to temperature. However, unlike most other resistive devices, the resistance of a thermistor decreases with increasing temperature. That's due to the properties of the semiconductor material that the thermistor is made from. For some, that may be counterintuitive, but it is correct.
- They are inexpensive, rugged and reliable.
- They respond quickly.
- The Steinhart-Hart equation gives the reciprocal of absolute temperature as a function of the resistance of a thermistor.Using the Steinhardt-Hart equation, you can calculate the temperature of the thermistor from the measured resistance.The Steinhardt-Hart equation is: 1/T = A + B*ln(R) + C*(ln(R))3 R in W, T in oK