What is an Infrared Thermometer?

It is an online monitoring (non-power failure) high-tech detection technology. It combines photoelectric imaging technology, computer technology, and image processing technology. It receives infrared (infrared radiation) emitted by objects and displays its thermal image on a fluorescent screen. Therefore, the temperature distribution of the object surface can be accurately judged, which has the advantages of being accurate, real-time and fast.

Infrared thermometer

Is a

Infrared temperature measurement technology in the production process, product quality control and monitoring, equipment online

In 1672, people discovered

Infrared thermometer

There are three main types of infrared temperature measuring instruments:

When setting the measurement distance, make sure that the target diameter is equal to or larger than the measured spot size. The distance between object 1 marked on the right and the measuring instrument is positive, because the target is slightly larger than the measured spot size. The "object No. 2" is too far away because the target is smaller than the measured spot size, that is,

The right infrared thermometer

The choice of infrared thermometer can be divided into 3 aspects:

(1) In terms of 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 ambient temperature, window, display and output, protection accessories, etc .;

(3) 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 technology and continuous development, the best design and new development of infrared thermometers provide users with various functions and multi-purpose instruments, expanding the choice. Other options, such as ease of use, maintenance and calibration performance, and price. When selecting the thermometer type, you should first determine the measurement requirements, such as the measured target temperature, the measured target size, the measurement distance, the measured target material, the target environment, the response speed, the measurement accuracy, whether it is portable or online ; In the comparison of various existing thermometers, choose the model that can meet the above requirements; choose the best combination of performance, function and price among the many models that can meet the above requirements.

Determine the temperature range

Determine the temperature measurement range: The temperature measurement range is one of the most important performance indicators of the thermometer. Such as Raytek () product coverage is -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 considered 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 wavelength band of the spectrum will exceed the change in radiant energy caused by emissivity errors. Therefore, it is better to use short waves when measuring temperature. Generally speaking, the narrower the temperature measurement range, the higher the resolution of the output temperature monitoring signal, and the easier the accuracy and reliability can be solved. The temperature measurement range is too wide, which will reduce the temperature measurement accuracy. For example, if the measured target temperature is 1000 degrees Celsius, first determine whether it is online or portable, and if it is portable. There are many models that meet this temperature, such as 3iLR3, 3i2M, 3i1M. If the measurement accuracy is main, it is best to choose 2M or 1M model, because if you choose 3iLR type, its temperature measurement range is very wide, the high temperature measurement performance will be worse; if the user in addition to measuring the target of 1000 degrees Celsius, also take care Low temperature target, that had to choose 3iLR3.

Determine target size

Infrared thermometers can be divided into monochrome thermometers and dual-color thermometers (radiochromatic thermometers) according to the principle. For a monochrome thermometer, when measuring temperature, the area of the target to be measured should be filled with the field of view of the thermometer. It is recommended that the size of the target to be measured exceeds 50% of the field of view. If the size of the target is smaller than the field of view, the background radiant energy will enter the audiovisual notes of the thermometer and interfere with the temperature reading, causing errors. Conversely, if the target is larger than the field of view of the thermometer, it is determined by the ratio of the radiant energy in two independent wavelength bands. Therefore, when the target to be measured is small, not full of field of view, there is smoke, dust, and obstruction on the measurement path, and there is no significant impact on the measurement result when the radiation energy is attenuated. For small targets that are in motion or vibration, a colorimeter is the best choice. This is due to the small diameter and flexibility of the light, which can transmit light radiation energy on curved, blocked and folded channels.

For the Raytek two-color thermometer, it is not full of the scene, and there will be no influence on the measurement results when there is smoke, dust and blocking on the measurement path that attenuate the radiant energy. Even in the case of energy attenuation of 95%, the required temperature measurement accuracy can still be guaranteed. For targets that are small and moving or vibrating; sometimes moving in the field of view, or targets that may partially move out of the field of view, under these conditions, using a two-color thermometer is the best choice. If direct aiming between the thermometer and the target is impossible, and the measurement channel is curved, narrow, blocked, etc., a two-color fiber optic thermometer is the best choice. This is due to its small diameter and flexibility, which can transmit light radiation energy on curved, blocked and folded channels, so it can measure targets that are difficult to access, harsh conditions or close to electromagnetic fields.

Determine distance factor (optical resolution)

The distance coefficient is determined by the ratio of D: S, which is the ratio of the distance D from the thermometer probe to the target to the diameter of the target to be measured. If the thermometer must be installed away from the target due to environmental conditions, and you need to measure a small target, you should choose a thermometer with high optical resolution. The higher the optical resolution, that is, increasing the D: S ratio, the higher the cost of the thermometer. Raytek infrared thermometers D: S range from 2: 1 (low distance coefficient) to above 300: 1 (high distance coefficient). If the thermometer is far away from the target and the target is small, you should choose a thermometer with a high distance coefficient. For a fixed focal length thermometer, the minimum position of the light spot is at the focal point of the optical system, and the light spot near and far from the focal point will increase. There are two distance coefficients. Therefore, in order to accurately measure temperature at distances close to and away from the focus, the size of the measured target 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. Increasing D: S will reduce the received energy. If the receiving aperture is not increased, the distance coefficient D: S will be difficult to increase, which will increase the cost of the instrument.

Determine the wavelength range

The emissivity and surface characteristics of the target material determine the corresponding wavelength of the thermometer's spectrum. For high reflectivity alloy materials, there is a low or varying emissivity. In the high temperature region, the best wavelength for measuring metal materials is near-infrared, which can be selected from 0.8 to 1.0 m. Other temperature zones can be selected from 1.6m, 2.2m and 3.9m. Since some materials are transparent at a certain wavelength, infrared energy can penetrate these materials, and a special wavelength should be selected for this material. For example, the internal temperature of the glass should be 1.0 m, 2.2 m, and 3.9 m (the measured glass must be thick, otherwise it will transmit). The surface temperature of the glass should be 5.0 m. The low temperature area should be 8 to 14 m. For example, the measurement of polyethylene plastic film is 3.43m, polyester is 4.3m or 7.9m, and thickness of more than 0.4mm is 8-14m. For example, a narrow band of 4.64 m is used to measure CO in the flame, and 4.47 m is used to measure NO 2 in the flame.

Determine 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 final reading. It is related to the time constant of the photodetector, signal processing circuit and display system. The response time of Raytek's new infrared thermometer can reach 1ms. This is much faster than the contact temperature measurement method. If the target moves fast or measures a fast-heated target, a fast-response infrared thermometer should be selected; otherwise, a sufficient signal response cannot be achieved, which will reduce the measurement accuracy. However, not all applications require fast response infrared thermometers. When there is thermal inertia for stationary or target thermal processes, the response time of the thermometer can be relaxed. Therefore, the choice of the response time of the infrared thermometer should be adapted to the situation of the measured target. Determine the response time, mainly based on the speed of the target's movement and the temperature of the target. For a stationary target or target in thermal inertia, or the speed of existing control equipment is limited, the response time of the thermometer can be relaxed.

Signal processing function

In view of the difference between discrete processes (such as part production) and continuous processes, infrared thermometers are required to have multiple signal processing functions (such as peak hold, valley hold, and average value) to be used. To use peak hold, the temperature output signal is transmitted to the controller. Otherwise the thermometer reads the lower temperature between the bottles. If using peak hold, set the response time of the thermometer slightly longer than the time interval between the bottles so that at least one bottle is always under measurement.

Consideration of environmental conditions

The environmental conditions in which the thermometer is located have a great impact on the measurement results, and 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 is dust, smoke and steam, accessories such as protective covers, water cooling, air cooling systems, and air purifiers provided by the manufacturer can be used. These accessories can effectively solve the environmental impact and protect the thermometer to achieve accurate temperature measurement. When determining accessories, standardised services should be required wherever possible to reduce installation costs. The fiber optic two-color thermometer is the best choice when the noise, electromagnetic field, vibration or inaccessible environmental conditions, or other harsh conditions, smoke, dust or other particles reduce the measurement of the energy signal. A colorimeter is the best choice. Under noise, electromagnetic field, vibration and inaccessible environmental conditions, or other harsh conditions, a light color thermometer should be selected.

In sealed or hazardous materials applications (such as containers or vacuum boxes), the thermometer looks through the window. The material must be strong enough to pass the operating 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 location and window material should be selected to avoid mutual influence. In low-temperature measurement applications, Ge or Si materials are usually used as windows, which are not transparent to visible light, and the human eye cannot observe the target through the window. If the operator needs to pass through the window target, an optical material that transmits both infrared radiation and visible light should be used. For example, an optical material that transmits both infrared radiation and visible light should be used, such as ZnSe or BaF2 as the window material.

When there is flammable gas in the working environment of the thermometer, an intrinsically safe infrared thermometer can be selected, so as to perform safe measurement and monitoring in a certain concentration of flammable gas environment.

In the case of harsh and complicated environmental conditions, a system with a separate temperature head and display can be selected to facilitate installation and configuration. You can choose the signal output form that matches the current control equipment.

Calibration of infrared radiation thermometer

The infrared thermometer must be calibrated so that it can correctly display the temperature of the target being measured. If the thermometer used is out of temperature during use, it needs to be returned to the manufacturer or repair center for recalibration.

Effect of emissivity on infrared temperature measurement accuracy

We know that when any object is above absolute zero (-273.15 ), there will be infrared energy on the surface of the object, that is, infrared radiation is emitted. The higher the temperature, the stronger the infrared energy emitted! Infrared thermometers and infrared cameras measure the surface temperature of objects based on this feature. Since we know that infrared thermometers and infrared cameras measure the surface temperature of objects, they will inevitably be affected by the surface finish of the objects. Affected, the experiment proves that the closer the surface of the object is to the mirror surface (the stronger the reflection), the more the infrared energy emitted by the surface is more attenuated. Set a compensation coefficient, this compensation coefficient is the emissivity!