The choice of infrared thermometer can be divided into three aspects
Performance indicators, such as temperature range, spot size, working wavelength, measurement accuracy, response time, etc.; environmental and working conditions, such as ambient temperature, window, display and output, protection accessories, etc.; other options, such as ease of use, maintenance And calibration performance and price, etc., also have a certain impact on the choice of thermometer. With the continuous development of technology and technology, the best design and new progress of infrared thermometers provide users with various functional and multi-purpose instruments, expanding the choice.
Determine the temperature range:
The temperature measurement range is the most important performance index of the thermometer. For example, Raytek (Ray Thai) products cover a range of -50°C-+3000°C, but this cannot be done by one type of infrared thermometer. Each type of thermometer has its own specific temperature range. Therefore, the user's measured temperature range must be considered accurately and comprehensively, neither too narrow nor too wide. According to the law of blackbody radiation, the change of radiation energy caused by temperature in the short-wave band of the spectrum will exceed the change of radiation energy caused by emissivity error. Therefore, it is better to use short-wave as much as possible when measuring temperature.
Determine target size:
Infrared thermometers can be divided into single-color thermometers and two-color thermometers (radiation colorimetric thermometers) according to the principle. For monochromatic thermometers, when measuring temperature, the area of the target to be measured should fill the field of view of the thermometer. It is recommended that the measured target size exceed 50% of the field of view. 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 measurement readings, causing errors. Conversely, if the target is larger than the pyrometer's field of view, the pyrometer will not be affected by background outside the measurement area.
For Raytek (Lei Tai) two-color thermometer, its temperature is determined by the ratio of radiant energy in two independent wavelength bands. Therefore, when the target to be measured is small, does not fill the site, and there is smoke, dust, or obstruction on the measurement path that attenuates the radiation energy, it will not affect the measurement results. Even in the case of 95% energy attenuation, the required temperature measurement accuracy can still be guaranteed. For targets that are small and moving or vibrating; sometimes move within the field of view, or may partially move out of the field of view, under these conditions, the use of a two-color thermometer is the best choice. If it is impossible to aim directly between the thermometer and the target, and the measurement channel is bent, narrow, blocked, etc., the two-color fiber optic thermometer is the best choice. This is due to its small diameter, flexibility, and ability to transmit optical radiant energy over curved, blocked, and folded channels, thus enabling measurement of targets that are difficult to access, in harsh conditions, or near electromagnetic fields.
Determining Optical Resolution (Distance and Sensitivity)
The optical resolution is determined by the ratio of D to S, which is the ratio of the distance D between the pyrometer to the target and the diameter S of the measuring spot. If the thermometer must be installed far away from the target due to environmental conditions, and a small target must be measured, a thermometer with high optical resolution should be selected. The higher the optical resolution, that is, the higher the D:S ratio, the higher the cost of the thermometer.
Determine the wavelength range:
The emissivity and surface properties of the target material determine the spectral response or wavelength of the pyrometer. For high reflectivity alloy materials, there is low or varying emissivity. In the high temperature area, the best wavelength for measuring metal materials is near infrared, and the wavelength of 0.18-1.0μm can be selected. Other temperature zones can choose 1.6μm, 2.2μm and 3.9μm wavelength. Since some materials are transparent at a certain wavelength, infrared energy will penetrate these materials, and a special wavelength should be selected for this material. For example, the wavelengths of 10 μm, 2.2 μm and 3.9 μm are used to measure the internal temperature of the glass (the measured glass must be very thick, otherwise it will pass through) wavelengths; The wavelength of 3.43 μm is used for measuring polyethylene plastic film, and the wavelength of 4.3 μm or 7.9 μm is used for polyester. If the thickness exceeds 0.4mm, choose 8-14μm wavelength; another example is to measure C02 in the flame with a narrow band of 4.24-4.3μm wavelength, measure C0 in the flame with a narrow band of 4.64μm wavelength, and measure N02 in the flame with a wavelength of 4.47μm.
