Working principle of thermal sensors
Measurements are performed using the physical properties of infrared radiation. Infrared radiation, also known as infrared light, possesses properties such as reflection, refraction, scattering, interference, and absorption. Any substance with a certain temperature (above absolute zero) can radiate infrared radiation. Infrared sensors do not directly contact the object being measured, thus eliminating friction, and offer advantages such as high sensitivity and fast response.
Infrared sensors consist of an optical system, a detection element, and a conversion circuit. Optical systems can be classified into two types based on their structure: transmissive and reflective. Detection elements can be classified into thermal detection elements and photoelectric detection elements based on their working principle.
The most widely used type of thermistor is the thermistor. When a thermistor is exposed to infrared radiation, its temperature rises, its resistance changes, and this change is converted into an electrical signal output through a conversion circuit.
What are the functions of a thermistor?
1. Overheat protection of thermistor sensors
Overheat protection can be divided into direct and indirect protection. For low-current applications, a thermistor sensor can be directly connected in series with the load to prevent overheating damage and protect the device. For high-current applications, it can be used to protect relays, transistor circuits, etc. In either case, the thermistor is tightly integrated with the protected device, allowing for sufficient heat exchange between them. Once overheating occurs, the thermistor provides protection.
2. Thermistor sensors are used for measuring liquid levels.
When a heating current is applied to an NTC thermistor sensor, its surface temperature will be higher than the surrounding air temperature, resulting in a lower resistance. When the liquid level rises above its installation height, the liquid carries away its heat, causing its temperature to drop and its resistance to increase. By observing the change in resistance, it's possible to determine whether the liquid level is below a set value. The fuel level alarm sensor in a car's fuel tank utilizes this principle. Thermistors are also used in automobiles to measure oil temperature, coolant mixing, and other parameters.
The above is an introduction to the working principle of thermistors. After reading this, you should have a more comprehensive understanding of the principle of thermistors! When there is thermal radiation in the surrounding environment, thermistors absorb the corresponding radiant heat, causing their temperature to rise. Currently, thermistor sensors have broad market application prospects. With the development and maturation of related technologies, it is believed that the overall performance of thermistors will be greatly improved in the future.
