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According to different temperature coefficients, thermistors can be divided into two types of thermistors: positive temperature coefficient thermistor (PTC thermistor), negative temperature coefficient thermistor (NTC thermistor).
Use Thermistor For Indication Of Temperature
Thermistor applications are widely used in temperature control and temperature detection of household appliances such as induction cooker, electric pressure cooker, rice cooker, electric oven, disinfection cabinet, water dispenser, microwave oven, electric heater, industrial, environmental protection, meteorology, food processing equipment, and office automation equipment (such as copiers, printers), temperature detection and temperature compensation of instrument coils, integrated circuits, quartz crystal oscillators and thermocouples.
1. Through the liquid level control, place two negative temperature coefficient thermistors at the safe position of the high and low liquid level of the container, and apply a fixed heating current. The surface temperature of the thermistor at the bottom immersed in liquid is the same as the peripheral temperature, while the surface temperature of the thermistor resistor exposed to the air at a high place is higher than the peripheral temperature. If the liquid level floods the high resistance, the surface overflow decreases and the resistance value rises, the judgment circuit can use the resistance change to notify the alarm device in time, and the action circuit cuts off the liquid inlet pipeline to protect the liquid surface. If the liquid level drops to a low level, the bottom thermistor resistor is gradually exposed to the air. At this time, the surface temperature rises and the resistance decreases. The judgment circuit can use the resistance change to promptly notify the action circuit to open the liquid inlet pipe to supply liquid.
2. Temperature measurement as the thermistor resistor for measuring temperature, the general structure is simple and the price is low. Because of its large resistance, the contact resistance at the connection can be ignored, and it can be used in remote telemetry processes thousands of meters away.
3. Temperature compensation uses negative temperature characteristics, which can be used to compensate in some electronic devices. When the current and temperature increase due to overload, the resistance of the thermistor resistor increases the reverse pull-down current, which plays a role of compensation and protection. At this time, it should be noted that the positive temperature coefficient thermistor should be connected in series in the electronic circuit.
4. Temperature control in electromechanical protection and control, the critical point thermistor resistor is often connected in series in the relay control loop. When a device encounters a sudden failure and overloads, it will cause the temperature to rise. If the resistance value drops suddenly when the critical point is reached, the relay current exceeds the rated value of the operating current and acts to cut off and protect.