Infrared thermometers are divided into three categories and their principles
Three categories of infrared thermometers:
(1) Infrared thermometer for human use: Forehead-type infrared thermometer is a thermometer that uses the principle of infrared reception to measure the human body. When in use, you only need to conveniently align the detection window with the forehead, and you can quickly and accurately measure the body temperature.
(2) Industrial infrared thermometer: The industrial infrared thermometer measures the surface temperature of the object, and its optical sensor radiates, reflects and transmits energy, and then the energy is collected and focused by the probe, and then the information is converted into reading display by other circuits On the machine, the laser light equipped with this machine is more effective in aiming at the measured object and improving the measurement accuracy.
(3) Infrared thermometer for animals in animal husbandry: According to the Planck principle, the infrared non-contact thermometer for animals can accurately measure the body surface temperature of specific parts of the animal body surface, and correct the temperature difference between the body surface temperature and the actual temperature. Can accurately display the animal's individual body temperature.
Determining 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 wavelengths. 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 for measuring the internal temperature of the glass (the glass to be tested must be very thick, otherwise it will pass through); the wavelength of 5.0 μm is used for measuring the internal temperature of the glass; ; Another example is to measure polyethylene plastic film with a wavelength of 3.43 μm, and polyester with a wavelength of 4.3 μm or 7.9 μm.
Determine the response time: The response time indicates the reaction speed of the infrared thermometer to the measured temperature change, which is defined as the time required to reach 95% of the energy of the final reading, which is related to the time constant of the photodetector, signal processing circuit and display system. The response time of the new infrared thermometer can reach 1ms. This is much faster than the contact temperature measurement method. If the moving speed of the target is very fast or when measuring a fast-heating target, a fast-response infrared thermometer should be selected, otherwise the sufficient signal response will not be achieved, and the measurement accuracy will be reduced. However, not all applications require a fast-response infrared thermometer. For static or target thermal processes where thermal inertia exists, the response time of the pyrometer can be relaxed. Therefore, the choice of the response time of the infrared thermometer should be adapted to the situation of the measured target.
The optical resolution is determined by the ratio D to S, which is the ratio of the distance D between the pyrometer to the target and the diameter S of the measurement 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, i.e. increasing the D:S ratio, the higher the cost of the pyrometer.
Determining 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 wavelengths. 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 1.0 μm, 2.2 μm and 3.9 μm are used to measure the internal temperature of the glass (the glass to be tested must be very thick, otherwise it will pass through); the wavelength of 5.0 μm is used to measure the internal temperature of the glass; the wavelength of 8-14 μm is used for low measurement It is advisable; another example is to measure the wavelength of 3.43 μm for polyethylene plastic film, and the wavelength of 4.3 μm or 7.9 μm for polyester.
Determine the response time: The response time indicates the reaction speed of the infrared thermometer to the measured temperature change, which is defined as the time required to reach 95% of the energy of the final reading, which is related to the time constant of the photodetector, signal processing circuit and display system. The response time of Guangzhou Hongcheng Hong Kong CEM brand infrared thermometer can reach 1ms. This is much faster than contact temperature measurement methods. If the moving speed of the target is very fast or when measuring a fast-heating target, a fast-response infrared thermometer should be selected, otherwise the sufficient signal response will not be achieved, and the measurement accuracy will be reduced. However, not all applications require a fast-response infrared thermometer. For static or target thermal processes where thermal inertia exists, the response time of the pyrometer can be relaxed. Therefore, the choice of the response time of the infrared thermometer should be adapted to the situation of the measured target.
Signal processing function: Measuring discrete processes (such as parts production) is different from continuous processes, requiring infrared thermometers to have signal processing functions (such as peak hold, valley hold, average value). For example, when measuring the temperature of the glass on the conveyor belt, it is necessary to use the peak value to hold, and the output signal of its temperature is sent to the controller.
Consideration of environmental conditions: The environmental conditions of the thermometer have a great influence on the measurement results, which should be considered and properly resolved, otherwise it will affect the temperature measurement accuracy and even cause damage to the thermometer. When the ambient temperature is too high and there is dust, smoke and steam, you can choose the protective cover, water cooling, air cooling system, air blower and other accessories provided by the manufacturer. These accessories can effectively address environmental influences and protect the thermometer for accurate temperature measurement. When specifying accessories, standardize service should be requested as much as possible to reduce installation costs. When smoke, dust or other particles reduce the measurement energy signal, a two-color thermometer is the best choice. Under noise, electromagnetic field, vibration or inaccessible environmental conditions, or other harsh conditions, the fiber optic two-color thermometer is the best choice.
In applications with sealed or hazardous materials such as containers or vacuum chambers, the pyrometer views through a window. The material must be strong enough and pass through the operating wavelength range of the pyrometer being used. Also determine whether the operator also needs to observe through the window, so choose the appropriate installation location and window material to avoid mutual influence. In low-temperature measurement applications, Ge or Si materials are usually used as windows, which are opaque to visible light, and the human eye cannot observe the target through the window. If the operator needs to pass through the window target, an optical material that transmits both infrared radiation and visible light should be used. For example, an optical material that transmits both infrared radiation and visible light should be used as the window material, such as ZnSe or BaF2.
Simple operation and easy use: Infrared thermometers should be intuitive, easy to operate, and easy to be used by operators. Among them, portable infrared thermometers are small, light, and carried by people that integrate temperature measurement and display output. Temperature measuring instruments can display temperature and output various temperature information on the display panel, and some can be operated by remote control or computer software program.
In the case of harsh and complicated environmental conditions, a system with a separate temperature measuring head and display can be selected for easy installation and configuration. The signal output form matching the current control equipment can be selected. Calibration of the infrared radiation thermometer: the infrared thermometer must be calibrated so that it can correctly display the temperature of the measured target. If the temperature measurement of the thermometer used is out of tolerance during use, it needs to be returned to the manufacturer or the repair center for re-calibration.
