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Functions of the Thermistor Resistor

Functions of the Thermistor Resistor

1. Function 1 of the thermistor - temperature measurement


As a thermistor resistor for measuring temperature, the structure is generally simple and the price is relatively low. The thermistor without an outer protective layer can only be used in a dry place; the sealed thermistor is not afraid of moisture erosion and can be used in harsh environments. Because the resistance of the thermistor resistor is relatively large, the resistance and contact resistance of its connecting wire can be ignored. Therefore, the thermistor resistor can be used in long-distance temperature measurement of several kilometers, and the measurement circuit mostly uses a bridge.


2. Function 2 of the thermistor - temperature compensation


The thermistor resistor can compensate the humidity of certain components within a certain temperature range. For example, the moving coil in the head of the moving coil meter is made of copper wire, and the resistance increases with the temperature rising, causing temperature errors. Therefore, the thermistor with negative temperature coefficient can be connected in parallel with the manganese-copper wire resistance in the loop of the moving coil and then connected in series with the compensated component to offset the error caused by the internal temperature change.


3. Function 3 of the thermistor - overheat protection


Overheating protection is divided into direct protection and indirect protection. For small current occasions, the thermistor resistor can be directly connected to the load to prevent overheating damage to protect the device. For high current occasions, it can be used to protect relays, transistor circuits, etc. For example, the abrupt thermistor resistor is embedded in the stator winding of the motor and connected in series with the relay. When the motor is overloaded, the stator current increases, causing heat. When the temperature is greater than the sudden change point, the current in the circuit can change from a few tenths of milliamps to tens of milliamps, so the relay operates to achieve overheating protection.


4. Function 4 of the thermistor - liquid level measurement


When a certain heating current is applied to the NTC thermistor resistor, its surface temperature will be higher than the surrounding air temperature, and its resistance value is smaller at this time. When the liquid is higher than its installation height, the liquid will take away its heat, causing its temperature to drop and resistance to increase. Judging the change of its resistance value, you can know whether the liquid level is lower than the set value. The fuel level alarm sensor in the automobile fuel tank is made by using the above principles.

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