Working Principle and Application of Infrared Thermometer
1 Overview
In the production process, infrared temperature measurement technology plays an important role in product quality control and monitoring, equipment online fault diagnosis and protection, and energy saving. In the past 20 years, non-contact infrared thermometers have developed rapidly in technology, their performance has been continuously improved, their functions have been continuously enhanced, their varieties have continued to increase, their scope of application has also continued to expand, and their market share has increased year by year. Compared with contact temperature measurement methods, infrared temperature measurement has the advantages of fast response time, non-contact, safe use and long service life. Non-contact infrared thermometers include three series of portable, on-line and scanning, and are equipped with various options and computer software, and each series has various models and specifications. Among the various models of thermometers with different specifications, it is very important for users to choose the correct model of infrared thermometer.
Infrared detection technology is a key promotion project of national scientific and technological achievements during the "Ninth Five-Year Plan". The emitted infrared (infrared radiation) displays its thermal image on the fluorescent screen, thereby accurately judging the temperature distribution of the object surface, which has the advantages of accuracy, real-time, and speed. Due to the movement of its own molecules, any object continuously radiates infrared heat energy outward, thus forming a certain temperature field on the surface of the object, commonly known as "thermal image". Infrared diagnostic technology absorbs this infrared radiation energy to measure the temperature of the equipment surface and the distribution of the temperature field, so as to judge the heating condition of the equipment. At present, there are many test equipments using infrared diagnosis technology, such as infrared thermometer, infrared thermal TV, infrared thermal imager and so on. Equipment such as infrared thermal TVs and infrared thermal imaging cameras use thermal imaging technology to convert this invisible "thermal image" into a visible light image, making the test effect intuitive, high sensitivity, and able to detect subtle changes in the thermal state of the equipment and accurately reflect The internal and external heating conditions of the equipment have high reliability and are very effective in discovering hidden dangers of equipment.
Infrared diagnostic technology can make reliable predictions for early failure defects and insulation performance of electrical equipment, and improve the preventive test maintenance of traditional electrical equipment (preventive test is the standard introduced in the former Soviet Union in the 1950s) to the predictive state maintenance, which is also the modern electric power system. The direction of enterprise development. Especially now that the development of large units and ultra-high voltage has put forward higher and higher requirements for the reliable operation of the power system, which is related to the stability of the power grid. With the continuous development and maturity of modern science and technology, the use of infrared state monitoring and diagnostic technology has the characteristics of long-distance, no contact, no sampling, no disassembly, and has the characteristics of accuracy, speed, and intuition, and can monitor and diagnose electrical equipment online in real time. Most of the faults (almost can cover the detection of various faults of all electrical equipment). It has received much attention from domestic and foreign power industries (an advanced condition-based maintenance system widely used in foreign countries in the late 1970s), and has developed rapidly. The application of infrared detection technology is of great significance to improve the reliability and effectiveness of electrical equipment, improve the economic benefits of operation, and reduce maintenance costs. It is a very good method that is widely promoted in the field of predictive maintenance at present, and it can raise the maintenance level and the health level of equipment to a higher level.
Infrared imaging detection technology can be used to conduct non-contact detection of running equipment, photograph the distribution of its temperature field, measure the temperature value of any part, and diagnose various external and internal faults accordingly, with real-time, telemetry, intuitive and quantitative With the advantages of temperature measurement, it is very convenient and effective to detect the operating equipment and live equipment of power plants, substations and transmission lines.
The method of using a thermal imager to detect online electrical equipment is the infrared temperature recording method. Infrared temperature recording method is a new technology used in industry for non-destructive detection, testing equipment performance and mastering its operating status. Compared with traditional temperature measurement methods (such as thermocouples, wax sheets with different melting points, etc. placed on the surface or body of the measured object), the thermal imager can detect the temperature of the hot spot in real time, quantitatively, and online within a certain distance. , It can also draw the temperature gradient thermal image of the equipment in operation, and it has high sensitivity and is not disturbed by electromagnetic fields, so it is convenient for on-site use. It can detect thermally induced faults of electrical equipment with a high resolution of 0.05 °C in a wide range from -20 °C to 2000 °C, revealing such as heating of wire joints or clamps, and local hot spots in electrical equipment, etc.
Infrared diagnostic technology of live equipment is a new subject. It is a comprehensive technology that utilizes the heating effect of charged equipment, uses special equipment to obtain infrared radiation information emitted from the surface of the equipment, and then judges the status of the equipment and the nature of defects.
2. Infrared basic theory
In 1672, it was discovered that sunlight (white light) is composed of light of various colors. At the same time, Newton made the conclusion that monochromatic light is simpler in nature than white light. Use a dichroic prism to decompose sunlight (white light) into monochromatic lights of red, orange, yellow, green, blue, blue, purple, etc. In 1800, the British physicist F. W. Huxel discovered infrared rays when he studied various colored lights from the thermal point of view. When he was studying the heat of various colors of light, he deliberately blocked the first window of the dark room with a dark plate, and opened a rectangular hole in the plate, and a beam splitter prism was installed in the hole. When sunlight passes through the prism, it is decomposed into colored light bands, and a thermometer is used to measure the heat contained in different colors in the light bands. In order to compare with the ambient temperature, Huxel used several thermometers placed near the colored light band as comparative thermometers to measure the ambient temperature. During the experiment, he accidentally discovered a strange phenomenon: a thermometer placed outside the reddish light had a higher value than other temperatures in the room. After trial and error, this so-called high-temperature zone with the most heat is always located outside the red light at the edge of the light band. So he announced that in addition to visible light, there is also a "red light" invisible to the human eye in the radiation emitted by the sun. This invisible "red light" is located outside the red light and is called infrared light. Infrared is a kind of electromagnetic wave, which has the same essence as radio waves and visible light. The discovery of infrared is a leap in human understanding of nature, and it has opened up a new broad road for the research, utilization and development of infrared technology.
The wavelength of infrared rays is between 0.76 and 100 μm. According to the wavelength range, it can be divided into four categories: near infrared, mid-infrared, far-infrared, and extremely far-infrared. Its position in the continuous spectrum of electromagnetic waves is the area between radio waves and visible light. . Infrared radiation is one of the most extensive electromagnetic radiation in nature. It is based on the fact that any object will produce its own molecular and atomic irregular motions in a conventional environment, and continuously radiate thermal infrared energy, molecules and atoms. The more intense the movement, the greater the radiated energy, and vice versa, the smaller the radiated energy.
Objects with a temperature above zero will radiate infrared rays due to their own molecular motion. After the power signal radiated by the object is converted into an electrical signal by the infrared detector, the output signal of the imaging device can completely simulate the spatial distribution of the surface temperature of the scanned object one by one. After being processed by the electronic system, it is transmitted to the display screen and obtained The thermal image corresponding to the heat distribution on the surface of the object. Using this method, it is possible to realize the long-distance thermal state image imaging and temperature measurement of the target and analyze and judge.
