How To Choose Infrared Thermometer

With the continuous improvement of science and technology, there are more and more kinds of infrared thermometers. When we buy them, we can't help but feel at a loss. In the face of so many products, what should we do when purchasing?

 

We generally consider the following three aspects when purchasing:
1. Performance indicators, such as temperature range, spot size, working wavelength, measurement accuracy, response time, etc;

2. Environment and working conditions, such as ambient temperature, window, display and output, protection accessories, etc;

3. Other options, such as easy to use, maintenance and calibration performance and price, also have a certain impact on the selection of thermometer. With the continuous development of technology and technology, the design and new progress of infrared thermometer provide users with various functions and multi-purpose instruments, and expand the choice.

 

Determination of temperature measurement range
The temperature measuring range is an important performance index of the thermometer Zui. For example, time and Raytek products cover a range of - 50 ℃ - + 3000 ℃, 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 accurate and comprehensive, neither too narrow nor too wide. According to the law of blackbody radiation, the change of radiation energy caused by temperature will exceed that caused by emissivity error in the short band of spectrum. Therefore, shortwave should be selected as far as possible in temperature measurement.

 

Determine target size
According to the principle, infrared thermometer can be divided into monochromatic thermometer and bicolor thermometer (radiation Colorimetric Thermometer). For the monochromatic thermometer, the measured target area should be full of the field of view of the thermometer. It is suggested that the size of the measured object 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 optoacoustic branch of the thermometer and 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, the thermometer will not be affected by the background outside the measurement area.

 

Determination of optical resolution (range and sensitivity)
The optical resolution is determined by the ratio of D to s, which is the ratio of the distance d between the thermometer and the target and the diameter s of the measured spot. If the thermometer must be installed far away from the target due to the limitation of environmental conditions, and to measure small targets, the thermometer with high optical resolution should be selected. The higher the optical resolution is, the higher the D: s ratio is, the higher the cost of the thermometer is.

 

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 region, the best wavelength for measuring metal materials is near infrared, and the wavelength of 0.18-1.0 μ M can be selected. In other temperature regions, the wavelengths of 1.6 μ m, 2.2 μ m and 3.9 μ M can be selected. Because some materials are transparent at a certain wavelength, infrared energy will penetrate these materials, so a special wavelength should be selected for this material. For example, the wavelengths of 10 μ m, 2.2 μ m and 3.9 μ m (the glass to be measured should be very thick, otherwise it will pass through); the wavelength of 5.0 μ m should be selected for measuring the internal temperature of the glass; the wavelength of 8-14 μ m should be selected for the low detection area; and the wavelength of 3.43 μ m should be selected for the measurement of polyethylene plastic film, and the wavelength of 4.3 μ m or 7.9 μ m should be selected for polyacetic acid. If the thickness is more than 0.4mm, the wavelength of 8-14 μ m is selected; for example, the narrow-band wavelength of 4.24-4.3 μ m is used for the measurement of C02 in the flame, the narrow-band wavelength of 4.64 μ m is used for the measurement of C0 in the flame, and the wavelength of 4.47 μ m is used for the measurement of N02 in the flame.

 

Determine response time
The response time represents the reaction speed of the infrared thermometer to the measured temperature change, which is defined as the time required to reach 95% of the reading of Zui (only 5% energy is needed for two-color colorimetric fiber). It is related to the time constant of 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 fast heating target is measured, the fast response infrared thermometer should be selected, otherwise the signal response can not be enough, which will reduce the measurement accuracy. However, not all applications require fast response infrared thermometers. When the thermal inertia exists in the static or thermal process, the response time of the thermometer can be relaxed. Therefore, the selection of the response time of the infrared thermometer should adapt to the situation of the measured target.