The working principle and characteristics of nuclear radiation level meter

Abstract: Information on the working principle and characteristics of nuclear radiation level meters is provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. As long as the propagation speed of ultrasonic waves in the medium is known, the level of material can be determined from the propagation time. However, the speed of sound is also related to factors such as the composition, temperature and pressure of the medium. Therefore, it is difficult to regard the speed of sound as a constant constant. Generally use settings. For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the details of the working principle and characteristics of the nuclear radiation level meter. As long as the propagation speed of ultrasonic waves in the medium is known, the level of material can be determined from the propagation time. However, the speed of sound is also related to factors such as the composition, temperature and pressure of the medium. Therefore, it is difficult to regard the speed of sound as a constant constant. Generally, the speed of sound should be corrected by setting a correction tool. The so-called calibration tool is to install a measurement device composed of an ultrasonic probe (calibration probe) and a reflector at a fixed distance in the sound-guiding medium, as shown in Figure 5-30. For the liquid medium ultrasonic level gauge, the calibration tool should be installed at the lowest position of the liquid medium to avoid the influence of the liquid surface reflected sound waves. Similarly, for the gas medium ultrasonic level gauge, the calibration tool should be installed at the top of the container. in the gas medium. If the ultrasonic pulse is transmitted from the probe and returns to the probe after ~ time, and travels through the correction section with a distance of 2sQ, then the actual speed of sound becomes the sound speed of the measurement section.„It is equal to the speed of sound in the correction section, then it can be obtained according to the formula: It is obvious from the formula that the measurement of the liquid level becomes the measurement time t and t0. When measuring, the speed of sound is different along the height direction, such as the density of the measured medium along the height direction. When the distribution is uneven or there is a temperature gradient, the floating arm type sound velocity correction tool can be used. The upper end of the correction tool is connected with a float, and the lower end is equipped with a rotating shaft, so that the position of the reflector of the correction tool rises and falls with the change of the liquid level, so that the correction probe and the measuring probe transmit and receive the ultrasonic wave passing through the state of the liquid is similar, so as to eliminate the errors due to differences in propagation speed. The measurement range of ultrasonic level measurement can be from the order of millimeters to more than tens of meters. The accuracy is 1% without the correction tool, and 0.1% after the correction tool is added. The phenomenon that the nucleus of a radioactive isotope emits various particles or rays with a certain energy in the nuclear decay is called nuclear radiation. There are three types of rays emitted by nuclear radiation, 0 and 7. where a-rays consist of positively charged O; particles’P-rays are composed of negatively charged 0 particles, and 7-rays are composed of neutral photons. At present, the radiation sources (or radioactive sources) used in level measuring instruments include radioactive isotopes such as cobalt c60Q and cesium cf7. Both isotopes emit stronger y-rays and have longer half-lives (the time it takes for a source of radiation to be reduced by half its intensity). For example, the half-life of cobalt C6^ is 5.3 years, and the half-life of cesium cf7 is 33 years. Compared with the 0: ray and the 0 ray, the 7-ray is less absorbed by the substance and can pass through the steel plate or other solid substances with a thickness of several tens of centimeters, so the 7-ray is widely used in the level detection. When rays pass through matter, they are scattered and absorbed by the atoms of the matter and lose some of their energy. After the ray passes through the material layer, its energy intensity attenuates exponentially with the thickness of the material layer, which can be expressed as in the formula, /G is the ray intensity before hitting the medium; / is the ray intensity after passing through the medium; A is the medium Absorption coefficient of rays; H is the thickness of the medium. When the radiation source is selected and the measured medium is known, both /0 and / are fixed values, then the relationship between the thickness of the medium // and the intensity of the ray after passing through the medium / can be expressed as The ray intensity after passing through the medium /, then the thickness of the medium, that is, the level F can be obtained. The ability of different media to absorb rays is different. The absorption ability of solid is the strongest, followed by liquid, and the weakest of gas. The nuclear radiation level meter consists of three parts: the radioactive source, the receiver and the display instrument. Its principle block diagram is shown in Figure 5-32. The radioactive source and receiver are placed on both sides of the container under test (measurement site), and the display instrument can be placed in the control room. The intensity of the radiation emitted by the radioactive source is /0. After passing through the container and the measured medium, it is received by the detector, and the detected radiation intensity / is converted into an electrical signal, which is amplified by the amplifier and sent to the display instrument for display. The ray detectors commonly used in industrial nuclear instruments include scintillation detectors, ionization chamber detectors and Geiger counters. The scintillation detector has high detection efficiency, can reduce the intensity of the radiation source of the instrument, and its working life is also long, up to several years; the disadvantages are high cost, slightly poor stability, and poor vibration resistance. According to the principle of nuclear radiation detection, it can be made into thickness gauge, level gauge and density gauge, etc. It can also be used to measure gas pressure, analyze material composition and perform non-destructive testing, and has a wide range of applications. In the application of radioisotopes, the y-ray level meter has a long application time and a large number.

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