How To Choose Infrared Thermometer Correctly Can Be Divided Into Three Aspects：

The selection of infrared thermometer can be divided into three aspects:

(1) Performance indicators, such as temperature range, spot size, working wavelength, measurement accuracy, window, display and output, response time, protection accessories, etc;

(2) Environmental and working conditions, such as environmental temperature, windows, display and output, protection accessories, etc;

(3) Other options, such as convenience of use, maintenance and calibration performance and price, also have a certain impact on the selection of thermometers.

With the development of technology and continuous development, the best design and new progress of infrared thermometers provide users with various functions and multi-purpose instruments, and expand the choice of space. Other options, such as ease of use, maintenance and calibration performance, and price, etc. When selecting the thermometer model, the measurement requirements shall be determined first, such as the temperature of the target being measured, the size of the target being measured, the measurement distance, the material of the target, the environment of the target, the response speed, the measurement accuracy, portable or online, etc.; in the comparison of the existing various types of thermometers, the instrument models that can meet the above requirements shall be selected; The best match in performance, function and price is selected among many models that can meet the above requirements.

Determine the temperature range

Determine the temperature range: the temperature range is the most important performance index of the thermometer. For example, Raytek (Raytek) products cover a range of -50 ℃ - +3000 ℃, but this can not be done by a type of infrared thermometer. Each type of thermometer has its own specific temperature range. Therefore, the temperature range of the user must be accurate and comprehensive, neither too narrow nor too wide. According to the blackbody radiation law, the change of radiation energy caused by temperature in the short band of spectrum will exceed the change of radiation energy caused by emissivity error. Therefore, short wave should be selected as much as possible in temperature measurement. Generally speaking, the narrower the temperature measurement range, the higher the resolution of the output signal of the monitoring temperature, and the easier to solve the accuracy and reliability. The temperature measurement accuracy will be reduced if the temperature range is too wide. For example, if the target temperature is 1000 degrees Celsius, determine whether online or portable, if it is portable. There are many models that meet this temperature, such as 3ilr3, 3i2m and 3i1m. If the measurement accuracy is the main one, it is better to choose 2m or 1m model. If 3ilr type is selected, the temperature measurement range is very wide, the high temperature measurement performance is worse; if the user takes care of the low temperature target in addition to the target of measuring 1000 ℃, then 3ilr3 must be selected.

Determine target size

According to the principle, infrared thermometer can be divided into monochromatic thermometer and two color thermometer (radiation Colorimetric Thermometer). For monochromatic thermometer, when measuring temperature, the target area to be measured shall be filled with the field of view of the thermometer. It is suggested that the target size measured exceeds 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 sound symbol of the thermometer to interfere with the temperature measurement reading, resulting in errors. On the contrary, if the target is larger than the field of view of the thermometer, it is determined by the ratio of radiation energy in two independent wavelength bands. Therefore, when the target is small and not full of field of view, smoke, dust and barrier exist in the measurement path, and the radiation energy is attenuated, it will not have a significant impact on the measurement results. For small and moving or vibrating targets, colorimetric thermometers are the best choice. This is because the light diameter is small and flexible, and the transmission radiation energy can be uploaded in the curved, blocked and folded channels.

For the Raytek (Raytek) two-color thermometer, it is not filled with the field. When smoke, dust and barrier exist in the measurement path, the radiation energy will not be affected. Even if the energy is reduced by 95%, the required temperature measurement accuracy can be guaranteed. For the target which is small and in motion or vibration; sometimes it moves in the field of view or may be partially removed from the field of view. Under this condition, the use of a two-color thermometer is the best choice. If the target and the thermometer can not be aimed directly, the two-color fiber optic thermometer is the best choice in the case of bending, narrow and blocked measuring channel. This is because of its small diameter and flexibility, it can upload the radiation energy in the curved, blocked and folded channels, so it can measure the target which is difficult to approach, under bad conditions or close to the electromagnetic field.

Determine distance coefficient (optical resolution)

The distance coefficient is determined by the ratio of d:s, that is, the ratio of distance d from the probe to the target of the thermometer and the diameter of the target being measured. If the thermometer must be installed far away from the target due to the limitation of environmental conditions, and small targets are to be measured, the high optical resolution thermometer shall be selected. The higher the optical resolution, that is, the higher the d:s ratio, the higher the cost of the thermometer. The range of the Raytek infrared thermometer d:s ranges from 2:1 (low distance coefficient) to higher than 300:1 (high distance coefficient). If the thermometer is far away from the target and the target is small, the thermometer with high distance coefficient should be selected. For the temperature measuring instrument with fixed focal length, the spot is the minimum position in the focus of optical system, and the spot near and far away from the focus will increase. There are two distance coefficients. Therefore, in order to measure the temperature accurately in the distance close to and away from the focus, the measured target size should be larger than the spot size at the focus. The zoom thermometer has a minimum focus position, which can be adjusted according to the distance to the target. If the receiving aperture is not increased, the distance coefficient d:s is difficult to increase, which will increase the cost of the instrument.

Determine the wavelength range

The emissivity and surface characteristics of the target materials determine that the corresponding wavelength of the thermometer has low or variable emissivity for high reflectivity alloy materials. In the high temperature region, the best wavelength of metal material measurement is near infrared, and 0.8-1.0 μ M can be selected. Other temperature zones can be selected as 1.6 μ m, 2.2 μ m and 3.9 μ M. Because some materials are transparent at a certain wavelength, infrared energy will penetrate these materials, so special wavelength should be selected for this material. For example, the wavelength of 1.0 μ m, 2.2 μ m and 3.9 μ m (the glass to be measured shall be thick or will pass through) is selected for the measurement of the glass internal temperature; the temperature of the glass surface is 5.0 μ m; the temperature measurement area is 8-14 μ M. For example, 3.43 μ m is selected for the measurement of polyethylene plastic film, 4.3 μ m or 7.9 μ m for polyester, and 8-14 μ m for polyester with thickness of more than 0.4mm. For example, the narrow band of CO in the flame is 4.64 μ m, and the NO2 in the flame is 4.47 μ M.

Determine response time

Response time is the reaction speed of infrared thermometer to the temperature change measured, which is defined as the time required to reach 95% of the final reading energy. It is related to the time constant of photodetector, signal processing circuit and display system. The response time of the new type of Raytek infrared thermometer can reach 1ms. This is much faster than contact type methods. If the target is moving fast or measuring the target with fast heating, it is necessary to select a fast response infrared thermometer, otherwise, it will reduce the measurement accuracy if it fails to achieve enough signal response. However, not all applications require fast response infrared thermometers. When there is thermal inertia in the static or target thermal process, the response time of the thermometer can be relaxed. Therefore, the response time of infrared thermometer should be adapted to the situation of the target. The response time is determined mainly according to the target speed and the target temperature change speed. For the static target or target parameter in thermal inertia, or the speed of existing control equipment is limited, the response time of the thermometer can be relaxed.

Signal processing function

Because the discrete process (such as parts production) and continuous process are different, it is required that infrared thermometer can be selected with multi signal processing functions (such as peak value, valley value maintenance and average value). For example, when bottle on the temperature measurement conveyor belt is used, peak value shall be used to maintain, and the output signal of temperature shall be transmitted to the controller. Otherwise, the thermometer reads the lower temperature value between bottles. If the peak value is maintained, set the temperature detector response time slightly longer than the time interval between bottles, so that at least one bottle is always in measurement.

Environmental conditions consideration

The environmental conditions of the thermometer have a great influence on the measurement results, which should be considered and properly solved, otherwise, the accuracy of the temperature measurement will be affected or even damaged. When the environment temperature is high and dust, smoke and steam exist, the manufacturer can choose the protective sleeve, water cooling, air cooling system, air blower and other accessories provided by the manufacturer. These accessories can effectively solve environmental impact and protect the thermometer, and realize accurate temperature measurement. When determining accessories, standardized services should be required as far as possible to reduce installation costs. When smoke, dust or other particles reduce the signal of energy signal measurement under noise, electromagnetic field, vibration or difficult to access the environment, or other harsh conditions, fiber optic dichroic thermometer is the best choice. The color thermometer is the best choice. In the case of noise, electromagnetic field, vibration and inaccessible environment, or other adverse conditions, it is advisable to select a light Colorimetric Thermometer.

In sealed or dangerous material applications (such as containers or vacuum boxes), thermometers are observed through windows. The material must have sufficient strength and be able to pass the working wavelength range of the thermometer used. It is also necessary to determine whether the operator also needs to observe through the window, so the appropriate installation position and window material shall be selected to avoid mutual influence. In low temperature measurement, ge or Si materials are usually used as windows, which are not transparent to visible light, and human eyes cannot observe the target through the window. If the operator needs to pass through the window target, optical materials that can transmit both infrared radiation and visible light shall be used. For example, optical materials such as ZnSe or BaF2 shall be used as window materials.

When there is flammable gas in the working environment of the thermometer, the intrinsic safe infrared thermometer can be selected to conduct safety measurement and monitoring in a certain concentration of flammable gas environment.

In the case of severe and complex environmental conditions, the temperature measuring head and display can be selected separately for installation and configuration. The signal output mode matching with the current control equipment can be selected.

Calibration of infrared radiation thermometer

The infrared thermometer must be calibrated to show the temperature of the target correctly. If the temperature measurement instrument used is out of tolerance in use, it is necessary to return to the manufacturer or the maintenance center for re calibration.

The influence of emissivity on the accuracy of infrared temperature measurement

We know: when any object is higher than absolute zero (-273.15 ℃), the infrared energy will be emitted on the surface of the object. The higher the temperature, the stronger the infrared energy emitted! The infrared thermometer and infrared thermograph measure the temperature of the object surface according to this characteristic. Since we know that infrared thermometers and infrared thermometers are measuring objects The temperature of the surface of the body will be affected by the surface finish of the object. The experiment shows that the closer the surface of the object is to the mirror (the stronger the reflection), the more the infrared energy attenuation is emitted on the surface of the object, so we need to compensate the attenuation of the infrared energy on the surface of different objects, that is, to set a compensation coefficient, which is the emission coefficient Rate!