Principles and Composition of Infrared Thermometers
The temperature measurement principle of an infrared thermometer is to convert the radiation energy emitted by an object (such as molten steel) into an electrical signal. The magnitude of the infrared radiation energy corresponds to the temperature of the object (such as molten steel) itself. Based on the magnitude of the converted electrical signal, the temperature of the object (such as molten steel) can be determined.
Working principle of infrared thermometer
The infrared thermometer consists of an optical system, a photodetector, a signal amplifier, signal processing, display output, and other components. The optical system concentrates the infrared radiation energy of the target within its field of view, and the size of the field of view is determined by the optical components and their positions of the thermometer. Infrared energy is focused on the photodetector and converted into corresponding electrical signals. The signal is amplified and processed by a signal processing circuit, and then converted into the temperature value of the measured target after being calibrated according to the algorithm and target emissivity of the instrument's internal therapy.
In nature, all objects with temperatures above absolute zero are constantly emitting infrared radiation energy into the surrounding space. The
magnitude and wavelength distribution of infrared radiation energy of an object are closely related to its surface temperature. Therefore, by measuring the infrared energy radiated by an object itself, its surface temperature can be accurately determined, which is the objective basis for infrared radiation temperature measurement.
A blackbody is an idealized radiator that absorbs radiation energy of all wavelengths without any reflection or transmission of energy, and its surface emissivity is 1. However, the actual objects that exist in nature are almost not blackbodies. In order to clarify and obtain the distribution law of infrared radiation, a suitable model must be selected in theoretical research. This is the quantized oscillator model of body cavity radiation proposed by Planck, which derived Planck's law of blackbody radiation, namely the spectral radiance of blackbody radiation expressed in wavelength. This is the starting point of all infrared radiation theories, hence it is called the blackbody radiation law. The radiation level of all actual objects depends not only on the radiation wavelength and 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 to make the blackbody radiation law applicable to all practical objects, a proportionality coefficient related to material properties and surface states, namely emissivity, must be introduced. This coefficient represents the degree to which the thermal radiation of an actual object is close to blackbody radiation, with values between zero and values 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 affecting emissivity are: material type, surface roughness, physical and chemical structure, and material thickness.
