Infrared temperature measurement technology is playing an important role in product quality control and monitoring, equipment online fault diagnosis, safety protection, and energy conservation. In the past two decades, non-contact infrared thermometers have been rapidly developed in technology, performance has been continuously improved, and the scope of application has also been continuously expanding. Market share has increased year by year. Compared with contact temperature measurement methods, infrared temperature measurement has the advantages of fast response time, non-contact, safe use, and long service life.
Guangzhou Hong Cheng Hong Kong CEM brand non-contact infrared radiation temperature measurement products include portable, online and scanning three series, and with a variety of optional accessories and the corresponding computer software, each series in a variety of models and specifications. In various specifications of various types of thermometers, the correct selection of infrared thermometer model is very important for the user. Here only the thinking steps of how to correctly select the thermometer model are provided for the buyer's reference.
Infrared thermometer working principle
Understanding the working principle, technical indicators, environmental working conditions and operation and maintenance of infrared thermometers is to help users select and use infrared thermometers correctly.
All objects above absolute zero emit infrared radiation energy to the surrounding space. The infrared radiation characteristics of an object - the size of the radiation energy and its distribution by wavelength - have a very close relationship with its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, it can accurately determine its surface temperature, which is the objective basis for infrared radiation temperature measurement.
Black body radiation law: The black body is an idealized radiator. It absorbs all wavelengths of radiation energy, no energy is reflected and transmitted, and its surface has an emissivity of 1. It should be pointed out that there is no real black body in nature, but in order to understand and obtain the infrared radiation distribution law, a suitable model must be selected in theoretical research. This is Planck's quantum oscillator model of body cavity radiation, which is derived. Planck's law of blackbody radiation, which is the wavelength of the blackbody spectral irradiance, is the starting point of all infrared radiation theory, so called the blackbody radiation law.
The effect of the emissivity of an object on radiation temperature measurement: The actual objects present in nature are hardly black. The radiation amount of all actual objects depends on the wavelength of the radiation and the temperature of the object, and also relates to the types of materials constituting the object, the preparation method, the thermal process, and the surface conditions and environmental conditions. Therefore, in order for the law of blackbody radiation to apply to all real objects, a proportional coefficient, namely the emissivity, must be introduced in relation to the properties of the material and the surface state. The coefficient represents the degree of closeness of the thermal radiation of the actual object to blackbody radiation, with values ​​between zero and less than one. According to the law of radiation, as long as the emissivity of the material is known, the infrared radiation characteristics of any object are known.
The main factors influencing the emissivity are: material type, surface roughness, physical and chemical structure and material thickness.
When measuring the target temperature with an infrared radiation thermometer, the infrared radiation amount of the target in its band is first measured, and then the temperature of the measured target is calculated by the thermometer. The monochromatic thermometer is proportional to the amount of radiation in the band; the dual pyrometer is proportional to the ratio of the radiation in both bands.
Infrared system: infrared thermometer consists of optical system, photodetector, signal amplifier and signal processing, display output and other components. The optical system converges the target infrared radiation energy within its field of view. The size of the field of view is determined by the optical components of the pyrometer and its position. The infrared energy is focused on the photodetector and converted to a corresponding electrical signal. The signal passes through the amplifier and the signal processing circuit, and is converted into the temperature value of the measured target after being corrected according to the algorithm and target emissivity of the internal therapy of the instrument.
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; environment 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, also have a certain impact on the choice of thermometer. With the development of technology and continuous development, the best design and new progress of infrared thermometers have provided users with various functions and multi-purpose instruments, which has expanded the choice.
Determine the temperature measurement range: The temperature measurement range is the most important performance indicator of the thermometer. If the Hong Kong CEM brand product coverage is -50 °C - +2200 °C, but this can not be done by a model of infrared thermometer. Each type of thermometer has its own specific temperature range. Therefore, the user's measured temperature range must be considered accurate and comprehensive, neither too narrow nor too wide. According to the law of black body radiation, the change of the radiant energy caused by temperature in the short wavelength band of the spectrum will exceed the change of the radiant energy caused by the emissivity error. Therefore, it is better to use the short wave as far as possible when measuring temperature.
Determine the target size: Infrared thermometer based on the principle can be divided into monochrome thermometer and two-color thermometer (radiometer colorimeter). For monochromatic thermometers, when measuring temperature, the measured target area should be full of thermometer field of view. It is recommended that the measured target size exceed 50% of the size of the field of view. If the target size is smaller than the field of view, background radiation energy will enter the thermometer's visual symbol and interfere with the temperature readings, 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 sensitive)
The optical resolution is determined by the ratio of D to S, which is the ratio of the distance D from the pyrometer to the target and the diameter S of the measurement spot. If the pyrometer must be installed far away from the target due to environmental conditions, but also to measure a small target, you should choose a high-resolution optical thermometer. The higher the optical resolution, ie the increase in the D:S ratio, the higher the cost of the pyrometer.
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 are low or varying emissivities. In the high temperature region, the best wavelength for measuring metallic materials is near-infrared, and wavelengths of 0.18-1.0 μm can be selected. Other temperature zones are available with wavelengths of 1.6μm, 2.2μm and 3.9μm. Since some materials are transparent at a certain wavelength, infrared energy penetrates these materials, and special wavelengths should be selected for this material. If the internal temperature of the glass is measured, choose 1.0μm, 2.2μm and 3.9μm (the measured glass must be very thick, otherwise it will pass through); choose the wavelength of 5.0μm for measuring the internal temperature of the glass; choose 8-14μm wavelength for the low measurement area; For example, 3.43 μm wavelength is used for measuring polyethylene plastic film, and 4.3 μm or 7.9 μm wavelength is used for polyester. Thickness of more than 0.4mm choose 8-14μm wavelength; Another example is to measure the flame in the CO2 with a narrow band 4.24-4.3μm wavelength, the CO in the flame with a narrow band 4.64μm wavelength, measurement of NO2 in the flame with a wavelength of 4.47μm.
Determine the response time: The response time represents the reaction speed of the infrared thermometer to the measured temperature change and is defined as the time required to reach 95% of the final reading. It is related to the time constant of the photodetector, the signal processing circuit and the display system. Guangzhou Hong Cheng Hong Kong CEM brand infrared thermometer response time up to 1ms. This is much faster than contact temperature measurement. If the target's moving speed is fast or the target of rapid heating is measured, a fast-response infrared thermometer should be selected, otherwise, a sufficient signal response cannot be achieved and the measurement accuracy will be reduced. However, not all applications require a fast-response infrared thermometer. When there is thermal inertia for a stationary or target thermal process, the response time of the thermometer can be relaxed. Therefore, the choice of response time of the infrared thermometer should be compatible with the situation of the target being measured.
Signal processing function: Measurement of discrete processes (such as part production) and different continuous processes require that the infrared thermometer have signal processing functions (such as peak hold, valley hold, average). When measuring the temperature of the glass on the conveyor belt, peak hold is used, and the temperature output signal is sent to the controller.
Consideration of environmental conditions: The environmental conditions of the thermometer are of great influence on the measurement results and should be considered and properly addressed. Otherwise, the accuracy of the temperature measurement may even affect the damage of the thermometer. When the ambient temperature is too high, dust, smoke, and steam are present, accessories such as protective covers, water cooling, air cooling systems, and air purifiers can be used. These accessories can effectively solve the environmental impact and protect the thermometer to achieve accurate temperature measurement. When determining attachments, standardized services should be required as much as possible to reduce installation costs. Dual-color thermometers are the best choice when smoke, dust, or other particles reduce the measurement power. Fiber optic dual-color thermometers are the best choice for noise, electromagnetic fields, vibration or inaccessible environmental conditions, or other harsh conditions.
In sealed or hazardous material applications (such as containers or vacuum boxes), the pyrometer observes through the window. The material must have sufficient strength and pass the operating wavelength range of the thermometer used. It is also necessary to determine whether the operator also needs to observe through the window, so choose the proper installation position and window material to avoid mutual influence. In cryogenic measurement applications, Ge or Si material is usually used as a window, not 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, such as ZnSe or BaF2, should be used as a window material.
The operation is simple and easy to use: The infrared thermometer should be intuitive, easy to use, and easy to use by the operator. The portable infrared thermometer is a compact, lightweight, portable device that combines temperature measurement and display output. The temperature measuring instrument can display temperature and output various temperature information on the display panel, and some can be operated by remote control or through a computer software program.
In the case of harsh and complex environmental conditions, it is possible to select a system in which the temperature measuring head and the display are separated to facilitate installation and configuration. The signal output form that matches the current control device can be selected.
Infrared radiation thermometer calibration: Infrared thermometer must be calibrated so that it correctly shows the temperature of the measured target. If the thermometer used in the use of temperature measurement error occurs, you need to return to the manufacturer or repair center to re-calibrate.