Temperature sensor non-contact
Its sensitive components are not in contact with the tested object, also known as non-contact temperature measuring instruments. This instrument can be used to measure the surface temperature of moving objects, small targets and objects with small thermal capacity or rapid temperature change (transient), as well as the temperature distribution of the temperature field.
The most commonly used non-contact thermometers are called radiation thermometers based on the basic law of black-body radiation. Radiation thermometry includes brightness method (see optical pyrometer), radiation method (see radiation pyrometer), and colorimetric method (see colorimetric thermometer). Various radiation temperature measurement methods can only measure the corresponding photometric temperature, radiation temperature, or colorimetric temperature. Only the temperature measured for a blackbody (an object that absorbs all radiation but does not reflect light) is the true temperature. If the true temperature of the object is to be measured, the emissivity of the material surface must be corrected. The emissivity of the material surface is not only determined by temperature and wavelength, but also related to the surface state, film and microstructure, so it is difficult to measure accurately. In automated production, it is often necessary to use radiation thermometry to measure or control the surface temperature of certain objects, such as the rolling temperature of steel strips, rolling roller temperature, forging temperature, and the temperature of various molten metals in smelting furnaces or crucibles in metallurgy. In these specific cases, it is quite difficult to measure the emissivity of the object surface. For automatic measurement and control of solid surface temperature, an additional reflector can be used to form a blackbody cavity together with the measured surface. The effect of additional radiation can increase the effective radiation and effective emission coefficient of the measured surface. By utilizing the effective emission coefficient and adjusting the measured temperature through an instrument, the true temperature of the measured surface can be obtained. The most typical additional reflector is a hemispherical reflector. The diffuse radiation of the measured surface near the center of the ball can be reflected back to the surface by the hemispherical mirror, forming additional radiation, thereby improving the effective emission coefficient ε Is the emissivity of the material surface, ρ Is the reflectivity of the reflector. As for the radiation measurement of the true temperature of gas and liquid media, the method of inserting a heat-resistant material tube to a certain depth to form a blackbody cavity can be used. Calculate the effective emission coefficient of the cylindrical cavity after reaching thermal equilibrium with the medium through calculation. In automatic measurement and control, this value can be used to correct the measured cavity bottom temperature (i.e. medium temperature) to obtain the true temperature of the medium.
Advantages of non-contact temperature measurement: The upper limit of measurement is not limited by the temperature resistance of the temperature sensing element, so there is no limit on the maximum measurable temperature in principle. For high temperatures above 1800 ℃, non-contact temperature measurement methods are mainly used. With the development of infrared technology, radiation temperature measurement has gradually expanded from visible light to infrared, and has been adopted from below 700 ℃ to room temperature with high resolution.
