A thermometric property is a property of an object, substance or system that varies with temperature. It can thus be used to measure temperature. A thermistor is a semiconductor whose resistance varies with/is dependent on temperature. The symbol used to represent a thermistor is:
It’s basically a resistor with a weird line through it. Here is what an actual thermistor looks like:
Evidently, the word thermistor is a combination of the words thermal and resistor. Magical right?
Types of thermistors
Thermistors come in two (2) flavours:
- Positive temperature coefficient (PTC) - the thermistor’s resistance increases as temperature increases
- Negative temperature coefficient (NTC) - the resistance decreases as temperature increases
Because of this behaviour, PTC thermistors are great for circuit protection. If the circuit becomes too hot, the resistance of the thermistor increases, thus decreasing the current (and therefore power) entering the circuit, allowing it to cool down.
NTC thermistors are more often used for temperature measurement. Temperature changes result in a change in the resistance of the thermistor and this new resistance results in a different signal.