Infrared thermometers can be divided into three categories:
(1) Performance indicators such as temperature range, spot size, operating wavelength, measurement accuracy, response time, etc; In terms of environment and working conditions, such as ambient temperature, windows, display and output, protective accessories, etc; Other factors such as ease of use, maintenance and calibration performance, and price also have a certain impact on the choice of thermometer.
(2) Determining the temperature measurement range is an important performance indicator of a thermometer. Each model of thermometer has its own specific temperature measurement range. Therefore, the user's measured temperature range must be considered accurately and comprehensively, neither too narrow nor too wide. According to the blackbody radiation law, the change in radiation energy caused by temperature in the short band of the spectrum will exceed the change in radiation energy caused by emissivity error. Therefore, short waves should be used as much as possible for temperature measurement.
(3) Infrared thermometers for determining target size can be divided into monochrome thermometers and two-color thermometers (radiation colorimetric thermometers) based on their principles. For monochrome thermometers, the area of the measured target should fill the thermometer's field of view during temperature measurement. It is recommended that the size of the target being tested exceed 50% of the field of view size. If the target size is smaller than the field of view, the background radiation energy will enter the visual and acoustic symbols of the thermometer and interfere with the temperature reading, causing errors. On the contrary, if the target is larger than the field of view of the thermometer, the thermometer will not be affected by the background outside the measurement area.
Determine optical resolution (distance sensitivity)
The optical resolution is determined by the ratio of D to S, which is the ratio of the distance D between the thermometer and the target to the diameter S of the measurement spot. If the thermometer must be installed far away from the target due to environmental conditions and needs to measure small targets, a high optical resolution thermometer should be selected. The higher the optical resolution, i.e. increasing the
D: S ratio, the higher the cost of the thermometer.
Determine wavelength range
The emissivity and surface properties of the target material determine the spectral response or wavelength of the thermometer. For high reflectivity alloy materials, there is a low or varying emissivity. In high-temperature areas, the optimal wavelength for measuring metal materials is near-infrared, which can be selected as 0.18-1.0mm wavelength. Other temperature zones can use wavelengths of 1.6mm, 2.2mm, and 3.9mm. Due to some materials being transparent at certain wavelengths, infrared energy can penetrate these materials, and special wavelengths should be selected for these materials. If measuring the internal temperature of glass, choose wavelengths of 1.0mm, 2.2mm, and 3.9mm (the measured glass should be very thick, otherwise it will pass through); Measure the internal temperature of the glass using a wavelength of 5.0mm; It is advisable to use a wavelength of 8-14mm for measuring low areas; For example, when measuring polyethylene plastic film, a wavelength of 3.43mm is used, while for polyester, a wavelength of 4.3mm or 7.9mm is used. Select wavelengths of 8-14mm for thicknesses exceeding 0.4mm; For example, CO2 in a flame is measured using a narrowband wavelength of 4.24-4.3mm, CO in a flame is measured using a narrowband wavelength of 4.64mm, and NO2 in a flame is measured using a narrowband wavelength of 4.47mm.
