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summary: This article introduces the working principle and characteristics of radar level meters and the advanced measurement technology of radar level meters. It also proposes precautions in the selection and installation of radar level meters and solutions to related problems in use. It conducts useful discussions for better mastering and using radar level meters. keywords: Radar material level meter principle and application selection and installation 1. Overview Material level is an important parameter in industrial production. There are many methods of material level measurement. Material level meters with different measurement principles can be used for different working conditions and media. There are several commonly used material level measuring instruments such as air blowing method, static pressure type, float type, weight type, ultrasonic, etc., all of which have their own characteristics and application ranges. Radar level gauges use advanced radar measurement technology and play an increasingly important role in industrial production due to their excellent performance, especially under harsh measurement conditions such as agitation, high temperature, large steam, highly corrosive media, and easy scarring in tanks. 2. Principle and technical performance Radar wave is a special form of electromagnetic wave. The radar level meter uses the special properties of electromagnetic waves to detect material level. The physical properties of electromagnetic waves are similar to visible light, and their propagation speed is equivalent to the speed of light. Its frequency is 300MHz~3000GHz. Electromagnetic waves can penetrate interference sources such as space vapor and dust, and are easily reflected when encountering obstacles. The better the conductivity or the greater the dielectric constant of the measured medium, the better the reflection effect of the echo signal. The higher the frequency of the radar wave, the smaller the emission angle, the greater the energy (magnetic flux or field strength) per unit area, the smaller the attenuation of the wave, and the better the measurement effect of the radar level meter. 1. Basic principles of radar level meter and components of radar level meter: It mainly consists of transmitting and receiving devices, signal processors, antennas, operation panels, displays, fault alarms and other parts. Transmission-reflection-reception is the basic working principle of radar level meter. As shown in the picture. The antenna of the radar sensor emits a minimum radar signal of 5.8GHz in the form of a beam. The reflected signal is still received by the antenna, and the running time of the radar pulse signal from transmission to reception is proportional to the distance from the sensor to the medium surface and the material level. Right now: h = H – vt/2 where h is the material level ； H is the height of the slot ； v is the radar wave speed ； t is the time interval between transmitting and receiving radar waves ； 2. Advanced technology of radar level meter measuring material level: (1) Application of new echo processing technology It can be known from the measurement principle of the radar level meter that the radar level meter measures the material level by processing the time when the radar wave is emitted from the probe to the surface of the medium and then returns to the probe. There are many interference signals mixed in the reflected signal. Therefore, the processing of real echo and the identification technology of various false echoes have become the key factors for the accurate measurement of the radar level meter. (2) Measurement data processing: Due to the influence of factors such as liquid level fluctuations and random noise, a large amount of noise must be mixed in the detection signal. In order to improve the accuracy of detection, the detection signal must be processed to eliminate noise as much as possible. After a large number of experimental verifications, the data smoothing method can achieve satisfactory results. This method can also effectively overcome the influence of the stirrer in the tank on the measurement. (3) Characteristics of radar level meter: Because the radar level meter adopts the above-mentioned advanced echo processing and data processing technology, and the radar wave itself has high frequency and good penetration performance, the radar level meter has better performance than contact level meters and similar non-contact level meters. ①Can measure continuously and accurately under harsh conditions. ②Simple operation and convenient debugging. ③Accurate, safe and energy efficient. ④No maintenance required and high reliability. ⑤Almost all media can be measured. 3. Issues that should be paid attention to during installation (1) When measuring liquid materials, the axis of the sensor should be kept vertical to the medium surface. ； When measuring solid materials, the sensor must be tilted at a certain angle because the solid medium will have a stacking angle. (2) Try to avoid devices that cause false reflections within the emission angle. In particular, avoid obstacles in the 1/3 cone-shaped emission area closest to the antenna (because the closer the obstacle is, the stronger the false reflected signal will be). If it cannot be avoided, it is recommended to use a refraction plate to refract away the excessively strong false reflection signals. This can reduce the energy density of false echoes and make it easier for the sensor to filter out false signals. (3) Avoid the feed port to avoid false reflections. (4) The sensor should not be installed in the center of the arched tank (otherwise the false echo received by the sensor will be enhanced), nor should it be installed very close to the tank wall. The best installation location is 1/2 of the radius of the tank. (5) Avoid installing in places with strong eddy currents. like: Due to stirring or strong chemical reactions, it is recommended to use a waveguide or bypass tube for measurement. (6) If the sensor is installed on the pipe, the antenna must extend from the pipe. The horn antenna extends out of the pipe by at least 10mm. Rod antenna take-up length is up to 100 or 250mm. The minimum pipe diameter is 250mm. The method of increasing the diameter of the nozzle can be adopted to reduce the interference echo generated by the nozzle. (7) About waveguide antenna: The inner wall of the waveguide must be smooth, and the waveguide with the opening below must reach the required minimum liquid level so that measurements can be made in the pipeline. The type plate of the sensor should be aligned with the axis of the waveguide opening. If the measured dielectric constant is less than 4, it is necessary to install a reflective plate at the end of the waveguide, or bend the end of the waveguide into a bend to refract away the reflected echo from the bottom of the container. 4. Problems and solutions in application. The radar level gauge used in some working conditions has some problems due to improper installation position and conditions of the sensor. The following will provide solutions to some problems in use for your reference. 1． The first way to solve the problem of scarring and frequent failures of the probe is to raise the installation position of the probe. However, sometimes the installation conditions are limited and cannot be raised. The method of interlocking the material level measurement value with the pump of the tank should be used to solve this problem.: Reduce the maximum material level setting value by about 0.5m. When the material level reaches the maximum value, the feed pump can be stopped or the discharge pump can be started. 2． The corresponding improvement method when the radar level meter is flooded. The way to solve this problem is to change the radar level meter to a waveguide type measurement. The waveguide radar level meter is still installed at the original opening. The waveguide is about 0.2m higher than the exhaust pipe. In this way, even if the slurry overflows from the exhaust pipe under severe working conditions, the material level meter antenna will not be submerged by the slurry. It also avoids the interference of the stirrer eddy current and the emergence of a large amount of steam from the probe, reducing damage to the probe. At the same time, due to the good focusing effect of the waveguide, the received radar wave signal is stronger, and good measurement results are achieved. Using the waveguide measurement method can improve the meter measurement conditions and improve the meter measurement performance, which has high promotion and application value. 3． About the effect of foam on measurements: Dry foam and wet foam can reflect radar waves back and have no effect on measurements. ； Neutral foam will absorb and diffuse radar waves, thus seriously affecting the reflection of echoes or even causing no echoes at all. When the surface of the medium is thick foam, the measurement error is large or cannot be measured. Under such working conditions, the radar level meter has no advantage, which is a limitation of its application. 4． Treatment of antenna scarring: Hanging materials with a small dielectric constant have no effect on the measurement in the dry state, while hanging materials with a high dielectric constant have an impact on the measurement. It can be purged with compressed air (or flushed with clean water), and the cooled compressed air can reduce the temperature of the flange and electrical components. Alkaline scabs can also be cleaned with acidic cleaning solutions, but material level measurement cannot be performed during cleaning. 5. Conclusion Radar level meter is currently the material level measuring instrument with the widest application range, the most accurate measurement and the most convenient maintenance among all types of material level measuring instruments. As its price further decreases and its cost-effectiveness increases, its application will become more and more widespread and it will play an increasingly important role in material level measurement. This article systematically explains it, aiming to help maintenance personnel better use and master it, hoping to provide some reference and help to everyone.