Thermistors are produced using basic ceramics technology by binding a mixture of oxide powders, selected from manganese, cobalt, copper, iron, titanium and nickel, together. The resulting material is formed into geometric shapes and leads are attached. Varying the amounts of each oxide used, and changing the temperature to which they are heated, result in different resistance and temperature characteristics.
Negative temperature coefficient (NTC) thermistors are those in which the resistance decreases with a temperature increase. They are best used when measuring a wide temperature range. In positive temperature coefficient (PTC) thermistors, the resistance increases with an increase in temperature. PTC thermistors are useful for when a change in resistance is needed at a particular temperature.
The relationship between a thermistor’s resistance and temperature is nonlinear. As the temperature changes slightly, the resistance changes sharply. Putting the measured resistance into particular equations directly gives the temperature. It is essential to calibrate the thermistor before use.