Non - contact temperature sensor
Non-contact temperature sensor sensor and the measured object is not in contact with each other, Called non-contact temperature measuring instrument. This thermometer can be used to measure moving objects, Small target and heat capacity is small or the temperature changes rapidly (transient) the surface temperature of the object. It can also be used to measure the temperature distribution of the temperature field.
Non-contact temperature sensor temperature law:
The most commonly used non-contact thermometer based on the basic law of blackbody radiation, Known as radiation thermometer. Radiation temperature measurement methods include: brightness method (see optical pyrometer), Radiation method (see radiation pyrometer), Colorimetric method (see colorimetric thermometer).
Various types of radiation temperature measurement method can only measure the corresponding photometric temperature, Radiation temperature or color temperature. Only the black body (absorb all the radiation does not reflect the light of the object) measured temperature is the real temperature.
1, to determine the true temperature of the object, It is necessary to modify the surface emissivity of the material. While the surface emissivity of the material depends not only on the temperature and wavelength, But also with the surface state, Coating and microstructure, etc., So it is difficult to accurately measure. In the automated production often need to use radiation temperature measurement method to measure or control the surface temperature of some objects.
2, such as metallurgical steel strip rolling temperature, Roll temperature, The temperature of the forging and the temperature of the various molten metals in the smelting furnace or crucible. In these specific cases, The measurement of the surface emissivity of the object is quite difficult.
3, for solid surface temperature automatic measurement and control, An additional reflector may be used to form a blackbody cavity together with the surface to be measured. The effect of additional radiation can increase the effective radiation and effective emission coefficient of the measured surface. Using the effective emission coefficient through the instrument on the measured temperature of the corresponding correction, The final temperature of the measured surface can be obtained. The most typical additional reflector is a hemispherical reflector. The diffuse radiation of the surface near the center of the sphere can be reflected back to the surface by the hemispherical mirror to form additional radiation, Thereby increasing the effective transmittance: Where ε is the surface emissivity of the material,ρ is the reflectivity of the mirror. As for the radiation measurement of the true temperature of the gas and liquid medium, It is possible to use a method of inserting a heat-resistant material tube to a certain depth to form a blackbody cavity. The effective emission coefficient of the cylindrical cavity after the heat balance with the medium is calculated. To correct the actual temperature of the medium.
Non-contact temperature sensor Advantages:
1>. The upper limit of the measurement is not limited by the temperature tolerance of the temperature sensing element, Therefore, there is no limit to the maximummeasurable temperature in principle. For high temperatures above 1800 ° C, Mainly used non-contact temperature measurement method. With the development of infrared technology, Radiation temperature gradually from the visible light to the infrared expansion, 700 ℃ below the room temperature have been used, And the resolution is high.
2>.Due to the measured medium is not directly in contact with, So do not have to consider some of the physical properties of the contact with the media, For example: adhesion, corrosion, wear, etc. will not cause damage to the sensor. And contact type will face the additional solution to these problems.
3>. Smaller by space. For some distance is far from being easily accessible to the measured target can be measured temperature long distance.
4>. For some inconvenient to touch the measurement of the target can be achieved measurement, Such as rotating machinery, moving targets and so on
Non-contact temperature sensor Disadvantages:
1, susceptible to environmental factors, such as thermal radiation
2, it is not easy to achieve long-term continuous measurement of the target.