How to choose an infrared temperature sensor?What should I pay attention to when choosing an infrared temperature sensor?

There are many Infrared temperature sensor products on the market, which makes us a little dazzled. So how to choose an Infrared temperature sensor correctly? It should start from the following aspects:

First, determine the requirements of the measurement target, considering the temperature and size of the target, the measurement distance, the material of the target, and the environment where the target is located;

Secondly, we must consider the response speed of the instrument, the measurement accuracy, whether it is used on-site or online monitoring, etc.; then choose the performance, function and price of the Infrared temperature sensor to become the best match; finally, consider the convenience of use, brand, and Quality assurance and service issues such as maintenance and calibration.

The specific analysis is as follows:

1. Understand the measurement temperature range The temperature measurement range is one of the most important performance indicators of Infrared temperature sensors. Each type of thermometer has its own specific temperature measurement.Range, it is recommended that you select an Infrared temperature sensor with an appropriate range according to the measurement requirements. The temperature range to be measured must be accurate and comprehensive, and don’t overdo it Narrow, not too wide. Excessive temperature measurement range will reduce the accuracy of temperature measurement. The temperature is too high and the price is expensive, which is not economically cost-effective; the temperature is too low to be full Meet the requirements. According to the law of black body radiation, the change in radiant energy caused by temperature in the short waveband of the spectrum will exceed the radiant energy caused by the emissivity error Therefore, it is better to choose short wave when measuring temperature. Generally speaking, the narrower the temperature measurement range, the higher the resolution of the output signal Degree of reliability is easy to solve.

2. Understand measurement accuracy and minimum resolution Measurement accuracy and resolution are two different concepts, which are easy to confuse. Measurement accuracy is to ensure that the measurement is accurate The only accurate indicator is also a key indicator to determine the performance of the Infrared temperature sensor. Resolution is the smallest measure when measuring a specific temperature.

3. Understanding the emissivity According to customer feedback, when using Infrared temperature sensors, measurement deviations often occur, 50% of which are the case.

Emissivity is the main cause of error. Since the Infrared temperature sensor is suitable for various occasions, the material and color of the surface of the object to be measured are different (especially It is a variety of pipes in the HVAC system), and its ability to emit infrared energy to the outside is different. By adjusting the emissivity, the material And the resulting measurement error. So whether the instrument has this function is very important.

4. Understand that the target size is the spot size, which is the area of the spot measured by the thermometer. The farther you are from the target, the larger the spot size. According to the principle, Infrared temperature sensors can be divided into monochromatic thermometers and two-color thermometers (radiometric colorimetric thermometers). For monochromatic thermometers, when measuring temperature, the measured target area should fill the field of view of the thermometer. It is recommended that the size of the measured target 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 thermometer to interfere with the temperature 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. For colorimetric thermometers, the temperature is determined by the ratio of radiant energy in two independent wavelength bands. Therefore, when the measured target is small, does not fill the field of view, smoke, dust, and barriers on the measurement path attenuate the radiation energy, it will not affect the measurement result. Even when the energy is attenuated by 95%, the required temperature measurement accuracy can still be guaranteed. For small objects that are in motion or vibration, the colorimetric thermometer is the best choice, because the light diameter is small, flexible, and can transmit light radiation energy in curved, blocked and folded channels, and can measure difficult .In order to approach, in bad conditions or close to the target of electromagnetic field.

5. Understand that the distance coefficient ratio (D:S) is the optical resolution, which refers to the ratio of the distance D between the Infrared temperature sensor to the target and the measurement spot diameter S. If you are far away from a target with a small diameter, you should choose a high-rate Infrared temperature sensor. The higher the distance coefficient ratio, the higher the cost of the Infrared temperature sensor. In order to obtain accurate temperature readings, the distance between the thermometer and the test target must be within an appropriate range. 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. For a thermometer with a fixed focal length, the focal spot of the optical system is the smallest spot, and the spot near and farther than the focal point will increase. There are two distance factors. Therefore, in order to accurately measure the temperature at the distance close to and far from the focus, the size of the target to be measured should be larger than the spot size at the focus. The zoom thermometer has a minimum focus position that can be adjusted according to the distance to the target. Increasing D:S will reduce the received energy. If the receiving aperture is not increased, the distance coefficient D:S is difficult to increase, which will increase the cost of the instrument.

6. Understanding the emissivity and surface characteristics of the target material in the wavelength range determines the corresponding wavelength of the spectrum of the thermometer. For high reflectivity alloy materials, there is a low or varying emissivity. In the high temperature zone, the best wavelength for measuring metal materials is near infrared, 0.8-1.0μm can be selected. Other temperature zones can choose 1.6μm, 2.2μm and 3.9μm. 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, use 1μm, 2.2μm and 3.9μm to measure the internal temperature of the glass (the glass to be measured must be very thick, otherwise it will pass through) wavelengths; use 5μm to measure the surface temperature of the glass; use 8-14μm to measure the low temperature zone. For example, use 3.43μm for polyethylene plastic film, 4.3μm or 7.9μm for polyester type, and 8-14μm if the thickness exceeds 0.4mm. For example, a narrow band of 4.64μm is used to measure CO in the flame, and 4.47μm is used to measure NO2 in the flame.

7. Understand the response time The response time is the time required for the Infrared temperature sensor to reach 95% of the energy of the final reading, indicating the reaction speed of the Infrared temperature sensor to the measured temperature change, and the time between it and the photodetector, signal processing circuit and display system Constant related. The choice of the response time of the Infrared temperature sensor should be adapted to the condition of the measured target. The response time is determined mainly based on the speed of the target's movement and the speed of the target's temperature change. If the speed of the target is fast or when measuring a rapidly heating target, a fast-response Infrared temperature sensor should be selected, otherwise the signal response will not be sufficient and the measurement accuracy will be reduced. However, not all applications require a fast response Infrared temperature sensor. For static or target thermal process with thermal inertia, response time You can relax the requirements.

8. Understanding of signal processing functions. In view of the difference between discrete processes (such as parts production) and continuous processes, Infrared temperature sensors are required to have multiple signal processing functions (such as peak hold, minimum hold, and average value) for selection, such as the temperature measurement conveyor belt When bottle is used, peak value hold is used, and the temperature output signal is transmitted to the controller. Otherwise, the thermometer reads the lower temperature value between the bottles. If peak hold is used, set the response time of the thermometer to be slightly longer than that of the bottle The time interval between so that at least one bottle is under measurement.

9. Understand the environmental conditions The environmental conditions in which the thermometer is located have a great influence on the measurement results. It 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 are dust, smoke and steam, you can choose the protective cover, water cooling, air cooling system, air purifier and other accessories provided by Tomoto DOBENY. These accessories can effectively solve the environmental impact and protect the thermometer to achieve accurate temperature measurement. When determining accessories, standardized services should be required as much as possible to reduce installation costs. When in noise, electromagnetic field, vibration or inaccessible environmental conditions, or other harsh conditions, smoke, dust or other particles reduce the measurement energy signal, the light colorimetric thermometer is the best choice.

If you need a non-contact Infrared temperature sensor, please contact the manufacturer of DOBENY: www.dobeny.com