Teach you how to correctly select the infrared thermometer
Select infrared thermometer can be divided into three areas:
(1) performance indicators, such as temperature range, spot size, operating wavelength, measurement accuracy, window, display and output, response time, protective accessories.
(2) environmental and working conditions, such as ambient temperature, window, display and output, protection accessories.
(3) other options, such as ease of use, maintenance and calibration performance and price, but also the choice of the thermometer have a certain impact.
With the technology and continuous development, infrared thermometer for the best design and new progress to provide users with a variety of functions and multi-purpose instrument, expanding the choice. Other options, such as ease of use, maintenance and calibration performance, and price. In the choice of thermometer model should first determine the measurement requirements, such as the measured target temperature, the measured target size, measurement distance, the measured target material, the target environment, response speed, measurement accuracy, portable or online and so on ; In the existing comparison of various types of thermometers, selected to meet the above requirements of the instrument model; in many to meet the above requirements to select the models in the performance, functionality and price of the best match.
1, determine the temperature range
Temperature measurement range is the most important performance indicators. Such as Raytek (Raytek) product coverage of -50 ℃ - +3000 ℃, but this can not be a type of infrared thermometer to complete. Each type of thermometer has its own specific temperature range. Therefore, the user's measured temperature range must be considered accurate, comprehensive, neither too narrow, not too wide. According to the law of blackbody radiation, the change of radiation energy caused by temperature will exceed the change of radiation energy caused by emissivity error in the short wavelength band of the spectrum, so it is better to use short wave as temperature measurement. In general, the narrower temperature range, monitor the temperature of the output signal resolution, the higher the accuracy of reliability is easy to solve. Temperature range is too wide, will reduce the temperature measurement accuracy. For example, if the measured target temperature is 1000 ° C, first determine the on-line or portable, if it is portable. Many models to meet this temperature, such as 3iLR3, 3i2M, 3i1M. If the measurement accuracy is the main, the best choice 2M or 1M models, because if the choice of 3iLR type, its wide temperature range, the high temperature measurement performance will be worse; If the user in addition to measuring 1000 ℃ target, but also take care of Low temperature target, it had to choose 3iLR3.
2, to determine the target size
According to the principle of infrared thermometer can be divided into monochromatic thermometer and two-color thermometer (radiation than color thermometer). For monochrome thermometer, in the temperature measurement, the measured target area should be filled with thermometer field of view. It is recommended that the measured object size exceed 50% of the field size. If the target size is smaller than the field of view, the background radiation energy will enter the thermometer as the audio-visual interference temperature reading, resulting in errors. Conversely, if the target is greater than the field of view of the thermometer, the thermometer will not be affected by the background outside the measurement area. For colorimetric pyrometers, the temperature is determined by the ratio of the radiated energy in two independent wavelength bands. So when the measured target is very small, do not fill the field of view, the measurement path of smoke, dust, block, the attenuation of radiation energy, do not have a significant impact on the measurement results. The colorimetric thermometer is the best choice for objects that are small and in motion or vibration. This is due to the small diameter of light, flexible, can bend, block and fold the channel transmission of optical radiation energy.
For a Raytek two-color pyrometer, the temperature is determined by the ratio of the radiated energy in two independent wavelength bands. Therefore, when the measured target is very small, not full of the scene, the measurement path of smoke, dust, blocking the radiation energy attenuation, will not have an impact on the measurement results. Even in the case of energy attenuation of 95%, but also to ensure the accuracy of the required temperature measurement. For targets that are small in size and in motion or vibration; sometimes moving in the field of view, or partially moving out of the field of view, a two-color thermometer is the best choice. If the thermometer and the target can not be directly aimed at, measuring channel bending, narrow, blocked, etc., the two-color fiber optic thermometer is the best choice. This is due to its small diameter and flexibility and the ability to transmit optical radiation energy on curved, blocked and folded channels, making it possible to measure targets that are difficult to access, harsh or near electromagnetic fields.
3, to determine the distance coefficient (optical resolution)
Distance coefficient from the D: S ratio to determine the temperature probe to the target distance between the D and the measured target diameter ratio. If the thermometer due to environmental constraints must be installed away from the target, but also to measure a small target, you should choose a high optical resolution of the thermometer. Optical resolution is higher, that is, increasing the D: S ratio, the higher the cost of the thermometer. Raytek Infrared Thermometer D: S ranges from 2: 1 (low range factor) to more than 300: 1 (high range factor). If the thermometer away from the target, and the target is small, you should choose the high-range coefficient of the thermometer. For a fixed focal length of the thermometer, the focal point of the optical system for the smallest spot position, near and far away from the focus position of the spot will increase. There are two distance coefficients. Therefore, in order to be close to and away from the focus on the accurate temperature measurement, the measured target size should be greater than the focal spot size, zoom thermometer has a minimum focus position, according to the distance to the target adjustment. Increase D: S, to reduce the energy received, if not increase the receiving aperture, distance coefficient D: S is very difficult to do, which would increase the cost of the instrument.
4. Determine the wavelength range
The emissivity and surface properties of the target material determine the corresponding spectral wavelength of the pyrometer with low or variable emissivity for high reflectivity alloy materials. In the high temperature region, the optimum wavelength of the metal material is near infrared, and it can be 0.8 ~ 1.0μm. Other temperature ranges are available in 1.6μm, 2.2μm and 3.9μm. Because some materials are transparent at certain wavelengths, infrared energy will penetrate these materials, the material should choose a special wavelength. Such as the measurement of the internal temperature of the glass selected 1.0μm, 2.2μm and 3.9μm (measured glass to be very thick, otherwise it will penetrate) wavelength; measured glass surface temperature selected 5.0μm; measured low temperature zone 8 ~ 14μm suitable. Such as the measurement of polyethylene plastic film selection 3.43μm, polyester 4.3μm or 7.9μm, thickness of more than 0.4mm 8-14μm. Such as the flame in the CO with a narrow band 4.64μm, measured in the flame with NO2 4.47μm.
5, determine the response time
The response time represents the response time of the infrared thermometer to the measured temperature change, defined as the time required to reach 95% of the final reading energy, which is related to the time constant of the photodetector, signal processing circuit and display system. Raytek (Raytek) new infrared thermometer response time of up to 1ms. This is much faster than the contact temperature measurement method. If the target is moving quickly or measuring rapid heating target, the choice of rapid response infrared thermometer, or fail to reach a sufficient signal response, will reduce the measurement accuracy. However, not all applications require a fast response infrared thermometer. The response time of the thermometer can be relaxed for the presence of thermal inertia in a stationary or target thermal process. Therefore, the choice of infrared thermometer response time and the measured target to adapt to the situation. Determine the response time, mainly based on the target speed and target temperature of the speed of change. For stationary targets or targets that are limited by thermal inertia or the speed of existing control equipment, the response time of the thermometer can be relaxed.
6, signal processing functions
In view of discrete processes (such as parts production) and continuous process different, so the requirements of infrared thermometer with multi-signal processing functions (such as peak hold, valley to maintain, the average), such as temperature conveyor belt on the bottle, To maintain the peak, the temperature of the output signal to the controller. Otherwise the thermometer reads the lower temperature value between the bottles. If the peak hold, set the thermometer response time is slightly longer than the time interval between the bottles, so at least one bottle is always in the measurement.
7, environmental considerations
Thermometer in which the environmental conditions have a great impact on the measurement results should be considered and properly addressed, otherwise it will affect the accuracy or even cause damage to the temperature measurement. When the ambient temperature is high, the presence of dust, smoke and steam conditions, manufacturers can use the protective cover, water cooling, air cooling systems, air purifiers and other accessories. These accessories can effectively solve the environmental impact and protect the thermometer to achieve accurate temperature measurement. In determining attachments, standardization services should be required wherever possible to reduce installation costs. When measuring noise, electromagnetic fields, vibration or difficult to access environmental conditions, or other harsh conditions, smoke, dust or other particles to reduce the measurement of energy signal, the optical fiber color thermometer is the best choice. Colorimetric thermometer is the best choice. In the noise, electromagnetic fields, vibration and difficult to access the environmental conditions, or other harsh conditions, should choose the light colorimetric thermometer.
In sealed or hazardous material applications (such as containers or vacuum boxes), the thermometer through the window for observation. The material must be strong enough to pass through the operating wavelength range of the thermometer used. But also to determine whether the operator also need to observe through the window, so to choose the appropriate installation location and window materials, to avoid mutual influence. In low-temperature measurement applications, usually Ge or Si material as a window, impermeable to visible light, the human eye can not observe the target through the window. Such as the operator through the window target, should be used both through infrared radiation and through the visible light of optical materials, such as the use of both infrared radiation and through the visible light of optical materials, such as ZnSe or BaF2 as a window material.
When the thermometer working environment in the presence of flammable gases, the choice of intrinsically safe infrared thermometer, which in a certain concentration of flammable gas environment for safety measurement and monitoring.
In the case of harsh environmental conditions, you can choose a separate head and monitor the system, in order to facilitate the installation and configuration. Can choose to match with the existing control device signal output form.
8, the infrared radiation thermometer calibration
Infrared thermometer must be calibrated in order to enable it to correctly display the measured target temperature. If the thermometer used in the use of temperature tolerance, you need to return to the factory or service center re-calibration.
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Contact:Eric Xie
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