Performance indicators of far-infrared thermometers
1, to determine the temperature range: temperature range is the most important performance indicators of the pyrometer. Each type of thermometer has its own specific temperature measurement range. Therefore, the user's measured temperature range must be considered accurately and thoroughly, neither too narrow nor too wide. According to the law of blackbody radiation, in the short wavelength band of the spectrum by the temperature-induced changes in radiant energy will exceed the change in radiant energy caused by emissivity errors.
2, determine the target size:Infrared thermometer can be divided into monochromatic pyrometer and two-colour pyrometer (radiation colorimetric pyrometer) according to the principle. For single-colour pyrometer, temperature measurement, the target area should be measured to fill the pyrometer field of view. It is recommended that the target size exceeds 50[%] of the field of view size. If the target size is smaller than the field of view, the background radiant energy will enter the pyrometer's visual acoustic signature and interfere with the temperature reading, resulting in an error. Conversely, if the target is larger than the pyrometer's field of view, the pyrometer will not be affected by the background outside the measurement area. In the case of a two-colour pyrometer, the temperature is determined by the ratio of the radiant energy in two separate wavelength bands. Therefore, when the measured target is very small and does not fill the field of view, the presence of smoke, dust, obstruction on the measurement path, there is attenuation of the radiant energy, are not significant impact on the measurement results. For targets that are small and in motion or vibration, a two-colour pyrometer is the best choice. This is due to the small diameter of the light, flexible, can be in the bending, blocking and folding of the channel to transmit optical radiation energy.
3, determine the distance coefficient (optical resolution): the distance coefficient is determined by the ratio of D: S, i.e., the ratio of the distance between the pyrometer probe to the target, D, and the diameter of the target to be measured. If the pyrometer must be installed away from the target due to environmental conditions, but also to measure small targets, you should choose a high optical resolution pyrometer. The higher the optical resolution, i.e. the larger the D:S ratio, the higher the cost of the pyrometer. If the pyrometer is far from the target and the target is small, a pyrometer with a high distance factor should be selected. For a fixed focal length pyrometer, the spot is smallest at the focal point of the optical system, and the spot increases both near and far from the focal point. There are two distance coefficients.
4, to determine the wavelength range: the emissivity of the target material and the surface characteristics of the spectral decision pyrometer corresponding wavelength for high reflectivity alloy materials, there are low or changing emissivity. In the high-temperature region, the best wavelength to measure the metal material is near infrared, can be selected 0.8 ~ 1.0 μm. Other temperature zones can be selected 1.6 μm, 2.2 μm and 3.9 μm. As some materials at a certain wavelength is transparent, infrared energy will be penetrated by these materials, such materials should be selected for special wavelengths.
5, to determine the response time: the response time indicates the infrared thermometer on the measured temperature change response speed, defined as the time required to reach the final reading of 95 [%] of the energy, which is related to the photodetector, the signal processing circuit and the display system time constant. If the target is moving very fast or when measuring a rapidly heating target, choose a fast response infrared thermometer, otherwise it will not achieve a sufficient signal response and will reduce the measurement accuracy. However, not all applications require a fast response infrared pyrometer. For stationary or target thermal processes there is thermal inertia, the response time of the pyrometer can relax the requirements.
6, signal processing capabilities: Given the discrete process (such as parts production) and continuous process is different, so the requirements of infrared thermometer with multiple signal processing capabilities (such as peak hold, valley hold, average value) available for selection, such as temperature measurement conveyor belt on the bottle, it is necessary to use the peak hold, and the temperature of the output signal transmitted to the controller. Otherwise the pyrometer reads out the lower temperature value between bottles. If the peak hold, set the thermometer response time is slightly longer than the time interval between bottles, so that at least one bottle is always in the measurement.
7, environmental conditions to consider: the environmental conditions in which the pyrometer has a great impact on the measurement results should be considered and properly addressed, otherwise it will affect the accuracy of temperature measurement or even cause damage. When the ambient temperature is high, the presence of dust, smoke and steam conditions, you can choose the manufacturer to provide a protective cover, water cooling, air cooling system, air blowers and other accessories. These accessories can effectively solve the environmental impact and protect the pyrometer to achieve accurate temperature measurement. In determining the accessories, standardised services should be required as far as possible to reduce installation costs.
8, infrared radiation thermometer calibration: infrared thermometer must be calibrated in order to make it correctly display the temperature of the target being measured. If the pyrometer used in the use of the temperature measurement over the difference, it is necessary to return to the manufacturer or maintenance centre to recalibrate.
