Function Of Thermistor
July 25, 2021
1. Thermistor is a resistor made of a special material, and its resistance value changes with temperature. According to the different coefficient of resistance change, thermistors are divided into two categories:
One type is called positive temperature coefficient thermistor (PTC), whose resistance value increases with temperature;
The other type is called Negative Temperature Coefficient Thermistor (NTC), whose resistance value decreases with increasing temperature.
2. Thermistor working principle
1) Positive temperature coefficient thermistor (PTC)
PTC is generally made of barium titanate as the main material, and a small amount of rare earth elements are added to barium titanate, and it is made by high temperature sintering. Barium titanate is a polycrystalline material. There is a crystal particle interface between the internal crystal and the crystal. When the temperature is low, the conductive electrons can easily cross the particle interface due to the internal electric field. At this time, its resistance value Will be smaller. When the temperature rises, the internal electric field will be destroyed, it is difficult for the conductive electrons to cross the particle interface, and the resistance value will rise at this time.
2) Negative temperature coefficient thermistor (NTC)
NTC is generally made of metal oxide materials such as cobalt oxide and nickel oxide. This type of metal oxide has fewer electrons and holes, and its resistance value will be higher. When the temperature rises, the number of electrons and holes inside will increase and the resistance value will decrease.
3. Advantages of thermistor
High sensitivity, the temperature coefficient of thermistor is more than 10-100 times larger than that of metal, and can detect temperature changes of 10-6℃; wide operating temperature range, normal temperature devices are suitable for -55℃~315℃, high temperature devices are suitable for temperature Above 315℃ (currently the highest can reach 2000℃), the low-temperature device is suitable for -273℃~-55℃; it is small in size and can measure the temperature of the space that other thermometers cannot measure.
4. Application of thermistor
The main application of a thermistor is as a temperature detection element, and temperature detection usually uses a thermistor with a negative temperature coefficient, that is, NTC. For example, commonly used household appliances, such as rice cookers, induction cookers, etc., all use thermistors.