Infrared thermometer

Temperature, pressure, current, voltage, etc. are basic physical quantities that people are familiar with. In the industrial field, it has a great impact on product quality, whole process control, etc. Among these basic physical quantities, it is much more difficult to measure and calibrate the temperature. This is because the influence of the "insulation" and "heat transfer" of the temperature system itself is very complex, which results in the large volume of the temperature measurement calibration system, the long stability time required, and the difficulty in improving the accuracy. It is not the same as the pressure system that the internal and external pressure can be increased without mutual influence as long as the pressure transmission pipeline leakage is increased/increased. In this way, it is easy to achieve rapid pressure transmission. The stability time only takes a few milliseconds and the measurement accuracy can easily reach several thousandths of a percent.

Let's take a look at a temperature measurement system with high accuracy and stability. It is impossible to improve/increase its "insulation", that is, to completely prevent heat transfer. People usually make a large enough volume think that the temperature field gradient of a small volume at its internal mass center is sufficiently balanced when it reaches thermal equilibrium, which is one of the important reasons why the volume of the temperature calibration source is huge. In addition, the heat transmission of a temperature system is also very complicated, and it is often completed by heat conduction, convection and radiation. It can be imagined that it is almost impossible to make its temperature suddenly change and reach the thermal balance. This is the conventional temperature calibration source. In order to improve/increase a certain uniformity of the temperature field, the device is large in size, and takes a long time to raise and lower the temperature, The inspection, maintenance and calibration of the temperature measurement system in the industrial field are time-consuming, laborious and expensive, and the reliability of the system is affected due to the repeated disassembly and assembly of the temperature probe.

The industrial field hopes to have a small, light and portable temperature correction source (thermostat) like the pressure calibrator. However, this small and portable temperature calibrator must overcome the disadvantages of poor uniformity and stability of the temperature field caused by the reduction of volume. To make the temperature rise and fall stable in a short time, there must be close cooperation between heating and cooling, It can reduce the heating and cooling time, and the cooling and heating in the miniaturized constant temperature bath also affect the uniformity of the temperature field. Therefore, the portable temperature corrector, which can achieve ultra small volume with a certain accuracy and quickly rise and fall, is a field application instrument that has been eagerly explored and developed in the field of temperature measurement technology for many years.

Infrared detection technology is a key promotion project of scientific and technological achievements in the "Ninth Five Year Plan". Infrared detection is an online monitoring (uninterruptible) high-tech detection technology, which integrates photoelectric imaging technology, computer technology, and image processing technology. It receives infrared (infrared radiation) emitted by objects, displays its thermal image on the fluorescent screen, and accurately judges the temperature distribution on the surface of objects, It is accurate, real-time and fast. Any object, due to the movement of its own molecules, constantly radiates infrared heat energy, thus forming a certain temperature field on the surface of the object, commonly known as "thermal image". The infrared diagnosis technology is to absorb the infrared radiation energy, measure the temperature of the equipment surface and the distribution of the temperature field, and then judge the heating condition of the equipment. There are many test equipment using infrared diagnostic technology, such as infrared thermometer, infrared thermal television, infrared thermal imager, etc. Devices such as infrared thermal television and infrared thermal imager use thermal imaging technology to transform this invisible "thermal image" into visible image, so that the test effect is intuitive, the sensitivity is high, the subtle thermal state changes of the equipment can be detected, and the internal and external thermal conditions of the equipment can be accurately reflected, with high reliability.

Infrared diagnosis technology can reliably predict the early fault defects and insulation performance of electrical equipment, so that preventive test maintenance of traditional electrical equipment (preventive test is the standard introduced from the former Soviet Union in the 1950s) can be improved to predictive condition maintenance, which is also the development direction of modern electric power enterprises. In particular, the development of large units and ultra-high voltage puts 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, maturity and improvement of modern science and technology, infrared condition monitoring and diagnosis technology has the characteristics of long-distance, non-contact, non sampling, non disassembly, and accurate, fast, intuitive, real-time online monitoring and diagnosis of most faults of electrical equipment (it can cover almost all kinds of fault detection of electrical equipment). It is highly valued by the domestic and foreign power industry (an advanced condition based maintenance system widely used in the late 1970s abroad), and has developed rapidly. The application of infrared detection technology is of great significance in improving the reliability of electrical equipment, improving the economic efficiency of operation and reducing the maintenance cost. It is a good means widely used in the field of predictive maintenance, and can also make the maintenance level and equipment health level to a higher level.

1) Take out the infrared thermometer from the box at the measured place;

2) Hold the handle of the thermometer with your right hand, press the switch with your index finger, and you will hear the sound of "BI-BI". When the power is turned on, the screen will display the temperature of the object you are facing. When measuring, pay attention to the distance coefficient K, which is K=D: S=12:1. It is generally understood that when the measuring range is 12m away, the area of the measured object is a circle with a diameter of 1m. If there is an object with a diameter of 1m at a place greater than 12m, The measured object temperature will not be accurate.

3) To measure an object, place the lens directly against the object to be measured, press and hold the switch to measure, and then the SCAN symbol will appear on the upper left side of the screen, indicating that the measurement is in progress. Release the switch, and the HOLD symbol will appear on the upper left side of the screen, which is the temperature of the object to be measured displayed on the screen.

4) To use the instrument in a dark or unclear environment, first release the power switch button, and then press the laser/backlight button. This is the laser/backlight symbol displayed on the screen. This is to press the switch for measurement, and you will see a red dot on the measured object, indicating that the temperature is being measured in this area. When not in use, release the power key, then press the laser/backlight button, press no laser once, press no backlight twice, and press no backlight and laser three times.

5) When testing a surface (such as airtight), the fixed-point method can be used, and each measurement must be recorded in time. The measured data is automatically kept for 7 seconds, no operation, and the power is automatically turned off after 30 seconds. The backlight automatically turns off after a delay of ten seconds.

Due to the needs of medical development, in many cases, ordinary thermometers can no longer meet the requirements of rapid and accurate temperature measurement, such as human body temperature measurement in places with high population density such as stations and airports. Although the technology of temperature measurement abroad is relatively mature, the domestic technology is still in the development stage. Therefore, in order to meet the needs of medical development, temperature measurement in special environment is needed, so as to effectively control and prevent the spread of special diseases such as SARS. It is urgent to design a thermometer with fast temperature measurement speed and high accuracy. In view of the low accuracy of the general industrial infrared thermometer, we improve the accuracy of the infrared thermometer according to the principle of this infrared thermometer, the selection of key components, the design of the aiming system, and the automatic adjustment of temperature compensation. We design a temperature measurement circuit with infrared wire, which is used for rapid human body temperature measurement in crowded and large flow situations.

1 Principle of infrared temperature measurement All objects in nature whose temperature is higher than zero (- 273.15 ℃) are constantly radiating electromagnetic waves including infrared wave band to the surrounding space due to the thermal movement of molecules, and the relationship between the radiation energy density and the temperature of the object itself conforms to the radiation law. Radiation principle outside the group - radiation law: where: E is the radiation emittance, W/m3; σ is the Stephen Boltzmann constant, 5.67 × 10-8W/(m2 · K4); ε is the emissivity of the object; T is the temperature of the object, in K; T0 is the ambient temperature around the object, in K. The temperature can be obtained by measuring the emitted E. The temperature measuring instrument made by using this principle is called infrared temperature instrument. This measurement does not need to contact the measured object, so it belongs to non-contact measurement. The temperature measurement range of infrared temperature instrument is very wide, from - 50 ℃ to more than 3000 ℃. In different temperature ranges, the wavelength distribution of the electromagnetic wave energy emitted by the object is different. In the normal temperature range (0~100 ℃), the energy is mainly concentrated in the mid infrared and far infrared wavelengths. The specific design of instruments used for different temperature ranges and different measuring objects is also different. According to the principle of formula (1), the infrared radiation measured by the instrument is:

Where: A is the optical constant, which is related to the specific design structure of the instrument; ε 1 is the emissivity of the measured object; ε 2 is the emissivity of the infrared thermometer; T1 is the temperature of the measured object (K); T2 is the temperature of the infrared thermometer (K); It is measured by a built-in temperature detector.    

The emissivity ε is a coefficient used to express the ability of an object to emit electromagnetic waves, and the value ranges from 0 to 1.0. 奡 An ideal radiation object is an object with a radiation rate of 1.0, which is physically called a blackbody. This is a theoretical concept. In fact, no object can reach the emissivity of 1.0. However, the actual blackbody which is very close to ε=1.0 can be manufactured for the calibration of thermometers. The ε value of all real objects, including the surfaces of various parts of the human body, is a value lower than 1.0. Since the value of ε is extremely difficult to measure and uncertain, after the instrument measures E, T1 calculated according to formula (2) will have errors. In actual work, the instrument is calibrated on the bold body with ε=1.0 and delivered. Only when the object with ε=1 is measured, its indication represents the actual temperature of the object. If the object ε is not equal to 1, the instrument reading does not represent the actual temperature of the object, and it needs to be corrected.    

The main radiation wavelength of the human body is 9~10 μ m of infrared ray. The measurement of the infrared energy radiated by the human body itself can accurately measure the temperature of the human body surface. Since the light within this wavelength range is not absorbed by the air, the infrared energy radiated by the human body can be used to accurately measure the temperature of the human body surface.    

The infrared radiation characteristics of a human body are closely related to its surface temperature. Therefore, the measurement of the infrared energy radiated by the human body itself can accurately measure the surface temperature of the human body. The great advantage of infrared temperature measurement technology is that the test speed is fast, and the test can be completed within 1s. Since it only receives the infrared radiation emitted by the human body, there is no other physical and chemical factors acting on the human body, so it is harmless to the human body.