Thermistor is a kind of sensitive element, and according to the different temperature coefficients, thermistor can be divided into positive temperature coefficient thermistor (PTC thermistor) and negative temperature coefficient thermistor (NTC thermistor). The typical characteristic of the thermistor is sensitive to temperature, and different temperatures show different resistance values. At the higher temperature, the resistance value of PTC thermistor is larger, and NTC thermistor is lower, which belongs to the same semiconductor device.
The main characteristics of the thermistor are:
(1) High sensitivity: its temperature resistance coefficient is 10 to 100 times more than metal, and it can detect the change of temperature of 10 to 6℃.
(2) Wide working temperature range: room temperature device applies to -55 to 315℃; high temperature device is applicable to higher than 315℃ (the highest can reach 2000℃); low temperature device is suitable for -273 to -55℃.
(3) Small volume: it can measure the temperature of the void that other thermometers cannot do, and the temperature of cavity and organism.
(4) Using easily: the resistance value can be selected arbitrarily between 0.1 and 100kΩ.
(5) Easy processing into complex shapes.
(6) Good stability and strong overload capacity.
The thermistor has many applications. Thermistors can be used as electronic circuits, which is applicable to temperature of instrument circuit andthermocouple cold end.By using the thermal properties of the NTC thermistor, the automatic gain control can be realized, which can constituteRC oscillator amplitude stabilization circuit, and that can reach the purpose of delaying circuit and protecting circuit. When the temperature is much larger than the ambient temperature, the resistance will be also related to radiation environmental conditions, so using this thermistor characteristic, special detecting elements are made, which apply to the flow meter, current meter, thermal analysis and gas analyzer. The PTC thermistor is mainly used for the overheating protection of electrical equipment,non-contact relay, constant temperature, automatic gain control, motor star, time delay, color TV automatic degaussing, temperature compensation etc.
