Thermistors

Thermistors are thermally-sensitive resistors whose prime function is to exhibit large, predictable and precise changes in electrical current when subjected to a corresponding change in temperature. They are used for measurement and control and have sensors which help regulate hot and cold. It does not matter if their temperature is changed by conduction, radiation or due to self-heating (power dissipated in the device). There are two basic types of thermistor. The first is the negative temperature co-efficient (NTC) which exhibits a decrease in electrical resistance when subjected to an increase in temperature. It is made from a pressed disc or rod of semiconducting material such as metallic oxides. The second type is the positive temperature efficient (PTC) which exhibits an increase in electrical resistance when subjected to an increase in temperature. It is made from doped polycrystalline ceramic (containing barium titanate). Thermistors are used as inroad current limiter to avoid gradual damage to components and to avoid blowing fuses or tripping circuit breakers. They are found as temperature sensors in cars to monitor things like the coolant and the oil temperature. In many domestic appliances such as toasters and coffee makers, they are able to measure temperature and regulate accordingly.