SunFounder ESP32 Starter Kit
5.26 Thermistor
A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard
resistors. The word is a combination of thermal and resistor. Thermistors are widely used as inrush current limiters,
temperature sensors (negative temperature coefficient or NTC type typically), self-resetting overcurrent protectors, and
self-regulating heating elements (positive temperature coefficient or PTC type typically).
• Thermistor - Wikipedia
Here is the electronic symbol of thermistor.
Thermistors are of two opposite fundamental types:
• With NTC thermistors, resistance decreases as temperature rises usually due to an increase in conduction elec-
trons bumped up by thermal agitation from valency band. An NTC is commonly used as a temperature sensor,
or in series with a circuit as an inrush current limiter.
• With PTC thermistors, resistance increases as temperature rises usually due to increased thermal lattice agitations
particularly those of impurities and imperfections. PTC thermistors are commonly installed in series with a
circuit, and used to protect against overcurrent conditions, as resettable fuses.
In this kit we use an NTC one. Each thermistor has a normal resistance. Here it is 10k ohm, which is measured under
25 degree Celsius.
Here is the relation between the resistance and temperature:
RT = RN * expB(1/TK - 1/TN)
• RT is the resistance of the NTC thermistor when the temperature is TK.
5.26. Thermistor 743
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