The selection of infrared thermometers can be divided into three aspects:
Determine the temperature measurement range:
The temperature measurement range is the most important performance indicator of a thermometer. The coverage range of Raytek products is -50 ℃ -+3000 ℃, but this cannot be achieved by a single model of infrared 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.
Determine target size:
Infrared thermometers 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.
For the Raytek dual color thermometer, its temperature is determined by the ratio of the radiated energy within two independent wavelength bands. Therefore, when the target being measured is small and not filled with the field, 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 energy attenuation of 95%, the required temperature measurement accuracy can still be guaranteed. For targets that are small and in motion or vibration; Sometimes targets that move within the field of view or may partially move out of the field of view, under these conditions, using a dual color thermometer is the best choice. If it is impossible to directly aim between the thermometer and the target, and the measurement channel is bent, narrow, or obstructed, a dual color fiber optic thermometer is the best choice. This is due to its small diameter, flexibility, and the ability to transmit optical radiation energy through curved, obstructed, and folded channels, making it possible to measure targets that are difficult to approach, have harsh conditions, or are close to electromagnetic fields.
Determine 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 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 0.18-1.0 μ m wavelength. Other temperature zones can use wavelengths of 1.6 μ m, 2.2 μ m, and 3.9 μ m. 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, wavelengths of 10 μ m, 2.2 μ m, and 3.9 μ m (the measured glass should be very thick, otherwise it will pass through) should be selected; Measure the internal temperature of the glass using a wavelength of 5.0 μ m; It is advisable to use a wavelength of 8-14 μ m for measuring low areas; For example, when measuring polyethylene plastic film, a wavelength of 3.43 μ m is used, while for polyacetylates, a wavelength of 4.3 μ m or 7.9 μ m is used. Select wavelengths of 8-14 μ m for thicknesses exceeding 0.4mm; For example, CO2 in the flame is measured using a narrowband wavelength of 4.24-4.3 μ m, C0 in the flame is measured using a narrowband wavelength of 4.64 μ m, and N02 in the flame is measured using a narrowband wavelength of 4.47 μ m.
