Infrared Thermometer Selection Guide
With the continuous improvement of science and technology, there are more and more types of infrared thermometers. We can’t help but be at a loss when purchasing. Faced with so many products, what should we do when shopping?
Below, our engineers will give you some suggestions.
When we buy, we generally consider the following three aspects:
1. Performance indicators, such as temperature range, spot size, working wavelength, measurement accuracy, response time, etc.;
2. Environmental and working conditions, such as ambient temperature, windows, 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 continuous development of technology, the best design and new developments of infrared thermometers provide users with various functions and multi-purpose instruments, expanding the choice.
Then I will give you a specific introduction:
Determine the temperature range
The temperature measurement range is an important performance index of the thermometer. For example, the coverage range of TIME and Raytek products is -50℃-+3000℃, but this cannot be done by one type of infrared thermometer. Each type of thermometer has its own specific temperature measurement range. Therefore, the user’s measured temperature range must be accurate and comprehensive, neither too narrow nor too wide. According to the law of black body radiation, the change in radiant energy caused by temperature in the short-wave band of the spectrum will exceed the change in radiant energy caused by the emissivity error. Therefore, it is better to use shortwave as much as possible when measuring temperature.
Determine the target size
Infrared thermometers can be divided into monochromatic thermometers and two-color thermometers (radiometric colorimetric thermometers) according to their principles. For a monochromatic thermometer, when measuring temperature, the measured target area should be full of the thermometer’s field of view. It is recommended that the size of the measured target exceeds 50% of the field of view. If the size of the target is smaller than the field of view, the background radiation energy will enter the visual and acoustic symbols of the thermometer to interfere with the temperature measurement reading, causing errors. Conversely, 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 the optical resolution (distance and sensitivity)
The optical resolution is determined by the ratio of D to S, which is the ratio of the distance D from the thermometer to the target and the diameter S of the measuring spot. If the thermometer must be installed far away from the target due to environmental constraints, and you want to measure a small target, you should choose a thermometer with high optical resolution. The higher the optical resolution, the higher the D:S ratio, and the higher the cost of the thermometer.
Determine the wavelength range
The emissivity and surface characteristics of the target material determine the spectral response or wavelength of the thermometer. For high reflectivity alloy materials, there are 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. Wavelengths of 1.6μm, 2.2μm and 3.9μm can be selected for other temperature zones. 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 internal temperature of the measuring glass should be 10μm, 2.2μm and 3.9μm (the glass to be measured must be very thick, otherwise it will pass through) wavelengths; the internal temperature of the measuring glass should be 5.0μm; the low measuring area should be 8-14μm; The wavelength of 3.43μm is used to measure polyethylene plastic film, and the wavelength of 4.3μm or 7.9μm is used for polyester. If the thickness exceeds 0.4mm, select 8-14μm wavelength; for example, measure CO2 in flame with narrow band 4.24-4.3μm wavelength, measure C0 in flame with narrow band 4.64μm wavelength, and measure N02 in flame with 4.47μm wavelength.
Determine the response time
The response time indicates the reaction speed of the infrared thermometer to the measured temperature change. It is defined as the time required to reach 95% of the energy of the final reading (two-color colorimetric fiber only needs 5% energy). It interacts with the photodetector and signal processing circuit. It is related to the time constant of the 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 speed of the target is fast or when measuring a rapidly heated target, a fast-response infrared thermometer should be selected, otherwise the signal response will not be adequate and the measurement accuracy will be reduced. However, not all applications require a fast-response infrared thermometer. When there is thermal inertia in a static or target thermal process, the response time of the thermometer can be relaxed. Therefore, the response time of the infrared thermometer should be selected to suit the conditions of the measured target.
I believe that through the above introduction, we should be able to choose a product that is suitable for our use when we buy an infrared thermometer.