Thermally sensitive materials are used to manufacture thermistors.
Depending on the temperature co- efficient of resistance value thermistors are classified as
NTC Thermistors: Negative temperature co- efficient
PTC Thermistors: Positive temperature co- efficient.
Symbol
Diagram
NTC Thermistors
NTC thermistors have negative temperature co-efficient of resistance where resistance of the resistive material decreases with increase in temperature.
NTC thermistors are used when continuous change of resistance is required over wide temperature range.
PTC Thermistors
PTC thermistors have positive temperature co-efficient of resistance in which resistance value decreases with decrease in temperature.
PTC thermistors are used when a drastic change in resistance is required at specific temperature.