Thermal Sensor

What Is Thermal Sensor?

A thermal sensor detects and measures temperature in various devices and systems. It is able to convert temperature information into usable electrical signals or data for use by other devices or systems. Thermal sensors are widely used in a variety of fields, including industrial automation, consumer electronics, automotive engineering, and medical equipment.

Types of Thermal Sensor

All thermal sensors monitor the temperature of a system or environment. Their primary function is to prevent overheating and adjust for changes in temperature-sensitive electrical parameters. The choice of a specific thermal sensor depends on the system's required accuracy and responsiveness. Thermal sensors come in various types, each with its own working principle and specific use case. Thermal sensors are categorized as follows:

Thermocouples

• Working principle: A thermocouple is a non-linear thermal sensor, with sensitivity and temperature ranges dependent on the types of metals combined. While thermocouples have low accuracy, they provide a wide operational range, spanning from -200℃ to 1750℃. They operate based on the Seebeck effect, where a temperature difference between two different metal wires generates a corresponding voltage difference. This voltage is proportional to the temperature change, and a look-up table is used to translate the voltage difference into temperature readings.

• Application: Thermocouples are widely used in industrial high-temperature measurement, furnace temperature monitoring, automotive, consumer applications, and other fields, because of their high-temperature resistance, fast response, and high precision.

Resistance Temperature Detectors (RTD)

• Working principle: RTDs sense temperature by detecting changes in resistance, requiring materials with a precise resistance-to-temperature relationship. Platinum is the preferred material for RTDs due to its linear response to temperature variations. Platinum RTDs are known for their stability, accuracy, and measurement repeatability, operating within a range of -270℃ to 850℃.

• Application: RTDS are used in situations where accurate temperature measurement is required, such as laboratory environments and process control systems.

Thermistors

• Working principle: Thermistors use polymer or ceramic materials instead of platinum and copper, which make them cheaper, but less accurate, than RTDs. A thermistor is a temperature-sensitive resistor whose resistance value changes with temperature. Common thermistors are positive temperature coefficient (PTC) and negative temperature coefficient (NTC).

• Application: Thermistors are mostly used for temperature measurement in the low-temperature range, such as temperature monitoring of electronic equipment and temperature control systems of household appliances.

Thermometers

• Working principle: Temperature measurements correspond to the volume change of the sensing element within the thermometer. The accuracy of a thermometer is influenced by the size of the device and the type of fluid used as the sensing element.

• Application: Thermometers are used to measure the temperature of any glass solids or liquids.

Infrared (IR) Sensors

• Working principle: IR sensors are electronic devices that detect temperature by emitting infrared radiation. These sensors are non-contact thermal sensors. With IR sensors, there is a trade-off between cost and accuracy: the more expensive the sensor, the greater its accuracy.

• Application: In the COVID-19 outbreak, people are using this non-contact heat sensor to check their body temperature.

Integrated Circuit (IC) Temperature Sensor

• Working principle: IC temperature sensors are based on semiconductor technology and typically provide either analog or digital signal outputs, which can be directly connected to electronic circuits or microprocessors. IC temperature sensors are highly accurate and linear over the temperature range of 55℃ to 155℃.

• Applications: IC temperature sensors are commonly found in CPU temperature monitoring, smartphones, wearable devices, and more.