What are the different types of temperature sensors in air conditioners?

What are the different types of temperature sensors in air conditioners?

Temperature sensors play a crucial role in the functioning of air conditioners, ensuring optimal cooling and energy efficiency. These sensors detect the temperature of the surrounding environment and provide feedback to the air conditioning system, allowing it to adjust its settings accordingly. In this article, we will explore the various types of temperature sensors used in air conditioners, their working principles, and their advantages and limitations.

1. Thermocouples

Thermocouples are one of the most commonly used temperature sensors in air conditioners. They consist of two different metal wires joined together at one end, forming a junction. When there is a temperature difference between the junction and the other end of the wires, a voltage is generated. This voltage is then measured and converted into a temperature reading.

Advantages of thermocouples:

  • Wide temperature range: Thermocouples can measure temperatures ranging from -200°C to over 2000°C, making them suitable for various air conditioning applications.
  • Fast response time: Thermocouples provide real-time temperature readings, allowing the air conditioner to quickly adjust its cooling output.
  • Durable and reliable: Thermocouples are robust and can withstand harsh environmental conditions, making them suitable for both indoor and outdoor air conditioning units.

Limitations of thermocouples:

  • Non-linear output: The voltage generated by thermocouples is non-linearly related to temperature, requiring additional calibration and compensation to obtain accurate readings.
  • Low accuracy: Thermocouples have lower accuracy compared to other temperature sensors, with typical errors ranging from 1 to 5 degrees Celsius.

2. Resistance Temperature Detectors (RTDs)

RTDs are another commonly used type of temperature sensor in air conditioners. They are made of a pure metal wire, such as platinum, wound around a ceramic or glass core. As the temperature changes, the resistance of the wire also changes, allowing the air conditioner to determine the temperature.

Advantages of RTDs:

  • High accuracy: RTDs offer excellent accuracy, typically within 0.1 degrees Celsius, making them suitable for precise temperature control in air conditioners.
  • Linear output: The resistance of RTDs changes linearly with temperature, simplifying the calibration process and ensuring accurate readings.
  • Stability: RTDs exhibit long-term stability and do not require frequent recalibration, providing reliable temperature measurements over an extended period.

Limitations of RTDs:

  • Limited temperature range: RTDs are not suitable for extreme temperature conditions, as their operating range is typically limited to -200°C to 600°C.
  • Slow response time: RTDs have a slower response time compared to thermocouples, which may result in a slight delay in the air conditioner’s adjustment to temperature changes.

3. Thermistors

Thermistors are temperature sensors that use the principle of resistance change with temperature. They are made of semiconductor materials with a negative temperature coefficient (NTC) or positive temperature coefficient (PTC). NTC thermistors have a decreasing resistance with increasing temperature, while PTC thermistors have an increasing resistance.

Advantages of thermistors:

  • High sensitivity: Thermistors offer high sensitivity to temperature changes, allowing for precise temperature control in air conditioners.
  • Compact size: Thermistors are small and can be easily integrated into air conditioning systems without occupying much space.
  • Cost-effective: Thermistors are relatively inexpensive compared to other temperature sensors, making them a popular choice for air conditioner manufacturers.

Limitations of thermistors:

  • Non-linear output: The resistance-temperature relationship of thermistors is non-linear, requiring additional calibration and compensation for accurate temperature readings.
  • Limited temperature range: The operating range of thermistors is typically limited to -50°C to 150°C, making them unsuitable for extreme temperature conditions.

4. Infrared (IR) Sensors

Infrared sensors, also known as non-contact temperature sensors, measure temperature by detecting the thermal radiation emitted by objects. They do not require physical contact with the object being measured, making them suitable for remote temperature sensing in air conditioners.

Advantages of infrared sensors:

  • Non-contact measurement: Infrared sensors can measure temperature without physically touching the object, making them ideal for applications where contact is not feasible or desirable.
  • Fast response time: Infrared sensors provide instantaneous temperature readings, allowing for quick adjustments in the air conditioning system.
  • Wide temperature range: Infrared sensors can measure temperatures ranging from -50°C to over 1000°C, making them suitable for various air conditioning environments.

Limitations of infrared sensors:

  • Dependent on surface emissivity: Infrared sensors rely on the emissivity of the object’s surface, which can vary and affect the accuracy of temperature measurements.
  • Interference from other heat sources: Infrared sensors may be affected by other heat sources in the vicinity, leading to inaccurate temperature readings.


Temperature sensors are essential components in air conditioners, enabling precise temperature control and energy efficiency. Thermocouples, RTDs, thermistors, and infrared sensors are among the most commonly used temperature sensors in air conditioning systems, each with its own advantages and limitations. Thermocouples offer a wide temperature range and fast response time but have lower accuracy. RTDs provide high accuracy and stability but have a limited temperature range. Thermistors are cost-effective and compact but have a non-linear output. Infrared sensors allow non-contact temperature measurement but can be affected by surface emissivity and interference from other heat sources. By understanding the different types of temperature sensors available, air conditioner manufacturers and users can make informed decisions to optimize cooling performance and energy efficiency.

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