Functions of Thermistors
Introduction
As the name implies, a thermistor is a resistor that is sensitive to heat. Now that we understand its basic characteristic, let us explore the functions of thermistors.
1. Functions of Thermistors – Overview
A thermistor is a type of resistive sensor; unlike standard fixed resistors, its resistance value changes with temperature. Classified as a type of variable resistor, it is widely used in various electronic components. Unlike resistance thermometers, which utilize pure metals, thermistors are typically made from ceramic or polymer materials. They also exhibit different temperature response characteristics: resistance thermometers are suitable for broad temperature ranges, whereas thermistors generally offer higher precision within a limited range—typically -90°C to 130°C.
2. Functions of Thermistors – Characteristics
Thermistors are sensitive components with a long history of development, a wide variety of types, and mature technology. Composed of semiconductor ceramic materials, most thermistors exhibit a negative temperature coefficient (NTC), meaning their resistance decreases as temperature rises. Key characteristics include high sensitivity, a wide operating temperature range, compact size, ease of use, suitability for mass production and complex shapes, good stability, and strong overload capability.
Due to their unique properties, semiconductor thermistors serve not only as measuring components but also as control and circuit compensation elements. They are widely used in fields such as home appliances, the power industry, telecommunications, military science, and aerospace, offering immense potential for future development.
3. One Function of Thermistors – Temperature Measurement
Thermistor sensors used for temperature measurement generally feature a simple structure and low cost. Unprotected thermistors are suitable only for dry environments, whereas sealed thermistors are resistant to moisture and can operate in harsher conditions. Due to the high resistance of thermistor sensors, the resistance of connecting wires and contact resistance can be considered negligible; consequently, they are suitable for long-distance temperature measurement (spanning several kilometers), typically utilizing bridge circuits.
4. Thermistor Application No. 2: Temperature Compensation
Thermistor sensors can provide temperature compensation for specific components within a certain temperature range. For instance, the moving coil in a moving-coil instrument is wound with copper wire; as the temperature rises, the resistance increases, leading to temperature-induced errors. To counteract this, a negative temperature coefficient (NTC) thermistor can be connected in parallel with a Manganin wire resistor, and this combination placed in series with the component requiring compensation, thereby canceling out errors caused by temperature fluctuations.
5. Thermistor Application No. 3: Overheat Protection
Overheat protection can be categorized into direct and indirect protection. In low-current applications, the thermistor sensor can be connected directly in series with the load to protect the device from overheating damage. In high-current applications, it can be used to protect components such as relays and transistor circuits. For example, a step-change (switching-type) thermistor sensor embedded in an electric motor's stator winding can be connected in series with a relay; when the motor is overloaded, the stator current increases, generating heat. Once the temperature exceeds the switching point, the circuit current jumps from a fraction of a milliampere to tens of milliamperes, triggering the relay and thereby providing overheat protection.
6. Thermistor Application No. 4: Liquid Level Measurement
When a specific heating current is applied to an NTC thermistor sensor, its surface temperature rises above that of the surrounding air, resulting in lower resistance. When the liquid level rises above the sensor's installation height, the liquid dissipates the heat, causing the sensor's temperature to drop and its resistance to increase. By monitoring this change in resistance, one can determine whether the liquid level has fallen below a preset value. Fuel level warning sensors in automotive fuel tanks operate based on this principle.
As the name implies, a thermistor is a resistor that is sensitive to heat. Now that we understand its basic characteristic, let us explore the functions of thermistors.
1. Functions of Thermistors – Overview
A thermistor is a type of resistive sensor; unlike standard fixed resistors, its resistance value changes with temperature. Classified as a type of variable resistor, it is widely used in various electronic components. Unlike resistance thermometers, which utilize pure metals, thermistors are typically made from ceramic or polymer materials. They also exhibit different temperature response characteristics: resistance thermometers are suitable for broad temperature ranges, whereas thermistors generally offer higher precision within a limited range—typically -90°C to 130°C.
2. Functions of Thermistors – Characteristics
Thermistors are sensitive components with a long history of development, a wide variety of types, and mature technology. Composed of semiconductor ceramic materials, most thermistors exhibit a negative temperature coefficient (NTC), meaning their resistance decreases as temperature rises. Key characteristics include high sensitivity, a wide operating temperature range, compact size, ease of use, suitability for mass production and complex shapes, good stability, and strong overload capability.
Due to their unique properties, semiconductor thermistors serve not only as measuring components but also as control and circuit compensation elements. They are widely used in fields such as home appliances, the power industry, telecommunications, military science, and aerospace, offering immense potential for future development.
3. One Function of Thermistors – Temperature Measurement
Thermistor sensors used for temperature measurement generally feature a simple structure and low cost. Unprotected thermistors are suitable only for dry environments, whereas sealed thermistors are resistant to moisture and can operate in harsher conditions. Due to the high resistance of thermistor sensors, the resistance of connecting wires and contact resistance can be considered negligible; consequently, they are suitable for long-distance temperature measurement (spanning several kilometers), typically utilizing bridge circuits.
4. Thermistor Application No. 2: Temperature Compensation
Thermistor sensors can provide temperature compensation for specific components within a certain temperature range. For instance, the moving coil in a moving-coil instrument is wound with copper wire; as the temperature rises, the resistance increases, leading to temperature-induced errors. To counteract this, a negative temperature coefficient (NTC) thermistor can be connected in parallel with a Manganin wire resistor, and this combination placed in series with the component requiring compensation, thereby canceling out errors caused by temperature fluctuations.
5. Thermistor Application No. 3: Overheat Protection
Overheat protection can be categorized into direct and indirect protection. In low-current applications, the thermistor sensor can be connected directly in series with the load to protect the device from overheating damage. In high-current applications, it can be used to protect components such as relays and transistor circuits. For example, a step-change (switching-type) thermistor sensor embedded in an electric motor's stator winding can be connected in series with a relay; when the motor is overloaded, the stator current increases, generating heat. Once the temperature exceeds the switching point, the circuit current jumps from a fraction of a milliampere to tens of milliamperes, triggering the relay and thereby providing overheat protection.
6. Thermistor Application No. 4: Liquid Level Measurement
When a specific heating current is applied to an NTC thermistor sensor, its surface temperature rises above that of the surrounding air, resulting in lower resistance. When the liquid level rises above the sensor's installation height, the liquid dissipates the heat, causing the sensor's temperature to drop and its resistance to increase. By monitoring this change in resistance, one can determine whether the liquid level has fallen below a preset value. Fuel level warning sensors in automotive fuel tanks operate based on this principle.
Jun 24,2026