What is the working principle of an infrared body thermometer?
The Temperature Measurement Principle of Infrared Thermometer
The principle of infrared thermometer temperature measurement is to convert the radiation energy of the infrared emitted by the measured object into electrical signals. The amount of infrared radiation energy is related to the temperature of the object itself, and the temperature of the object can be determined by converting it into an electrical signal. All objects above absolute zero will emit infrared radiation on their own. The function of an infrared thermometer is to collect the infrared radiation emitted by the object, and it will not emit any harmful radiation at all, so it is completely harmless to the human body. Some people misunderstand that the infrared thermometer emits radiation to the human body to produce readings, which is a misconception.
Temperature measurement emissivity of infrared thermometer
Blackbody is an idealized radiator that absorbs radiation energy of all wavelengths without any reflection or transmission of energy. Its surface emissivity is 1. However, almost all actual objects present in nature are not blackbodies. In order to understand and obtain the distribution law of infrared radiation, it is necessary to choose a suitable model in theoretical research, which is the quantized oscillator model of body cavity radiation proposed by Planck. This leads to the law of Planck blackbody radiation, which is the spectral radiance of blackbodies expressed in wavelength. This is the starting point of all infrared radiation theories, hence the blackbody radiation law. The radiation amount of all actual objects is not only dependent on the wavelength of radiation and the temperature of the object, but also on factors such as the type of material, preparation method, thermal process, surface state, and environmental conditions that make up the object. Therefore, in order for the blackbody radiation law to apply to all practical objects, it is necessary to introduce a proportional coefficient related to material properties and surface states, namely emissivity. This coefficient represents the proximity between the thermal radiation of the actual object and the blackbody radiation, with a value between zero and a value less than 1. According to the law of radiation, as long as the emissivity of a material is known, the infrared radiation characteristics of any object are known. The main factors that affect emissivity are material type, surface roughness, physicochemical structure, and material thickness. When measuring human body temperature, the emissivity is generally adjusted to 0.95 for the most accurate temperature measurement.
Human infrared thermometer
The infrared thermometer used to test human body temperature is called a human body infrared thermometer. However, it must be clarified that there is no specialized medical or industrial infrared thermometer, as the manufacturing principles of infrared thermometers are consistent. There is only a distinction between high-precision, high distance coefficient ratio, high-performance infrared thermometers, and high-precision, low distance coefficient ratio, and low-performance infrared thermometers. As long as the emissivity of the infrared thermometer is set to 0.95 (the emissivity of human skin is generally this value, and even if there is a difference, the impact is only within 0.3 degrees), it meets the requirements of human temperature measurement. (For example, all brands of cars can run at 40 km/h, while high-end cars may reach a speed of 200 km/h, but there is no distinction between cars that specifically run at 40 km/h and cars that specifically run at 200 km/h, only the difference between high and low performance cars.)
