Selection of Handheld Infrared Thermometers
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.
1. Determine the temperature measurement range
The temperature measurement range is the most important performance index of the thermometer. For example, the product coverage range is -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. Generally speaking, the narrower the temperature measurement range is, the higher the resolution of the output signal of the temperature monitoring is, and the accuracy and reliability are easy to solve. If the temperature measurement range is too wide, the temperature measurement accuracy will be reduced. For example, if the measured target temperature is 1000°C, first determine whether it is online or portable, and if it is portable. There are many models that meet this temperature, such as TI315, TI213 and so on.
2. Determine the target size
Infrared thermometers can be divided into single-color thermometers and two-color thermometers (radiation colorimetric thermometers) according to the principle. For a monochromatic thermometer, 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 a two-color pyrometer, the 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 moving 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 pyrometer and the target, and the measurement channel is bent, narrow, blocked, etc., the two-color fiber optic pyrometer is the best choice. This is due to their 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.
3. Determine the optical resolution
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. For example, the handheld infrared thermometer TI213 of the infrared era has a distance coefficient of 80:1. If it is 80 cm away from the target, the diameter of the measurement range is 1 cm. 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.
4. 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 glass to be tested 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, the wavelength of 8-14μm is used; for example, the narrow-band 4.24-4.3μm wavelength is used to measure C02 in the flame, the narrow-band 4.64μm wavelength is used to measure the C0 in the flame, and the 4.47μm wavelength is used to measure the N02 in the flame.
5. Determine 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 selection of the response time of the infrared thermometer should be suitable for the situation of the measured target.
6. Signal processing function
In view of the difference between discrete processes (such as parts production) and continuous processes, infrared thermometers are required to have multi-signal processing functions (such as peak hold, valley hold, average value) to choose from, such as when measuring the temperature of the bottle on the conveyor belt, it is To use peak hold, the temperature output signal is sent to the controller. Otherwise the thermometer reads a lower temperature value between the bottles. If using peak hold, set the thermometer response time to be slightly longer than the time interval between bottles so that at least one bottle is always under measurement.
7. 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. When the ambient temperature is high and there is dust, smoke and steam, the protective cover, water cooling, air cooling system, air purger and other accessories provided by the manufacturer can be selected.
