Thermometer principle of Infrared thermometer

The principle of temperature measurement of infrared thermometer is to convert the radiant energy of infrared rays emitted by an object into an electrical signal. The magnitude of infrared radiant energy corresponds to the temperature of the object itself. According to the size of the electrical signal, the temperature of the object can be determined.

Introduction

Infrared temperature measurement technology has been developed to scan and measure the temperature of the surface with heat change, determine the temperature distribution image, and quickly detect the hidden temperature difference. This is the infrared thermal imager. The infrared thermal imager was first applied to the military, the United States. TI has developed the world's first infrared scanning reconnaissance system in 19 years. In the future, infrared thermal imaging technology has been used in aircraft, tanks, warships and other weapons in the West, and the thermal imaging system as a reconnaissance target has greatly improved. The ability to search and hit targets. Fluke infrared thermometers are leading the way in civilian technology. However, how to make infrared temperature measurement technology widely used is still a research topic worth studying.

Thermometer principle

The infrared thermometer consists of an optical system, a photodetector, a signal amplifier, signal processing, and display output. The optical system converges the target infrared radiation energy within its field of view. The size of the field of view is determined by the optical components of the thermometer and their position. The infrared energy is focused on the photodetector and converted into a corresponding electrical signal. The signal passes through the amplifier and the signal processing circuit, and is converted to the temperature value of the measured object after being corrected according to the algorithm of the internal treatment of the instrument and the target emissivity.

In nature, all objects with temperatures above absolute zero are constantly emitting infrared radiation energy to the surrounding space. The magnitude of the infrared radiation energy of an object and its distribution by wavelength - is very closely related to its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, it can accurately measure its surface temperature, which is the objective basis on which infrared radiation is measured.

Infrared Thermometer Principle The black body is an idealized radiator that absorbs the radiant energy of all wavelengths. Without the reflection and transmission of energy, the surface emissivity is 1. However, the actual objects existing in nature are hardly black. In order to clarify and obtain the law of infrared radiation distribution, it is necessary to select a suitable model in theoretical research. This is the quantized vibrator model of body cavity radiation proposed by Planck. The law of Planck blackbody radiation, the blackbody spectral irradiance expressed in wavelength, is derived. This is the starting point of all infrared radiation theory, so it is called the blackbody radiation law. The amount of radiation of all actual objects depends on the wavelength of the radiation and the temperature of the object, as well as the type of material that makes up the object, the method of preparation, the thermal process, and the surface state and environmental conditions. Therefore, in order to apply the law of blackbody radiation to all practical objects, it is necessary to introduce a proportionality factor, ie, emissivity, related to the material properties and surface state. This coefficient indicates how close the thermal radiation of the actual object is to the blackbody radiation, with values between zero and less than one. According to the law of radiation, as long as the emissivity of the material is known, the infrared radiation characteristics of any object are known. The main factors affecting the emissivity are: material type, surface roughness, physical and chemical structure and material thickness.

When using the infrared radiation thermometer to measure the temperature of the target, first measure the amount of infrared radiation in the range of the target, and then calculate the temperature of the target by the thermometer. The monochromatic thermometer is proportional to the amount of radiation in the band; the two-color thermometer is proportional to the ratio of the amount of radiation in the two bands.