Analysis of advantages and disadvantages of high frequency and low frequency radar level meter

How does a radar level gauge work? How to choose high frequency and low frequency radar level meter? Working principle: Guided wave radar level meter is a microwave level meter, which is an application of radar positioning technology. It transmits energy waves through a device that emits energy waves (usually pulse signals), the energy waves are transmitted in the waveguide, the energy waves are reflected by obstacles, and the reflected energy waves are transmitted from the waveguide to the receiving device, and then received by The device receives the reflected signal. The change of the material level is determined according to the time difference of the movement process of the measured energy wave. The microwave signal is processed by the electronic device and finally converted into an electrical signal related to the material level. The electromagnetic wave emitted by the radar level gauge encounters the measured medium and is reflected, and the quality of the reflected echo reflects the application effect of the level gauge. Echo quality is defined as the ratio of the minimum echo amplitude (amplitude of echoes in harsh conditions) to the maximum noise amplitude (magnitude of false echoes, multipath reflections, etc.). The larger the echo quality value is, the better the application effect of the level meter is. The echo intensity is mainly affected by the following factors. The more stable the dielectric constant of the propagation medium, the more conducive to propagation. Radar waves are electromagnetic waves, and electromagnetic waves are not affected by the stability of the propagation medium during the propagation process, but are only related to their dielectric constant. This is a major difference between radar technology and ultrasonic technology. The flatter the surface of the measured medium, the greater the dielectric constant, the more conducive to echo reflection. Therefore, when considering on-site working conditions, special attention should be paid to these two aspects: (1) the distribution of the air permittivity between the antenna and the measured medium (2) the surface state of the measured medium and its permittivity. The advantages of radar level gauges are: not affected by air fluctuations, small attenuation with distance, and strong penetrating power. Disadvantages of radar level meter: 1) The performance of radar is affected by dielectric constant. In theory, radar attenuation in vacuum is extremely small. When there are materials that attenuate radar in the air, such as: dust powder with high dielectric properties (graphite, Ferro alloys, etc.), the water vapor is very large, and the measurement distance and effect will be affected. 2) The volatile gas of the measured medium will gather on the antenna, and the water vapor will condense on the antenna. At this time, it will affect the emission of radar waves. In severe cases, radar waves cannot be sent out. 3) The dielectric constant of the measured medium should not be too small. 4) Although the temperature and pressure have little effect on the radar, the radar antenna is made of materials, and the range of temperature and pressure that the radar can adapt to is related to the materials and sealing structures used. Low-frequency radar level gauges have the advantage of relatively low prices, but in the main application fields, they are gradually eliminated products. Analogous to the ultrasonic level meter, in order to obtain a better echo, the working frequency of the transducer is about 40KHz, the wavelength is about 9mm, and the opening angle of the transmitted wave is 7°-8°. The higher the operating frequency, the smaller the opening angle, but the smaller the range. Compared with the ultrasonic wave, to obtain the echo of the above-mentioned effect, when the operating frequency of the radar level meter is 26GHz, its wavelength is 11mm. When a horn with a diameter of 100mm is used, the emission wave with an opening angle of 7°-8° can be obtained. If the operating frequency of the radar is 6GHz, the operating frequency of the ultrasonic wave is 10KHz. However, the ultrasonic level meter with a working frequency of 10 kHz is not ideal for various indicators in the level measurement, and is especially not suitable for the measurement of solid material level. Compared with low-frequency radar, the advantages of high-frequency radar level gauge: 1) High-frequency radar level gauge (mainly refers to 26GHz and 24GHz) has high energy and small beam angle (generally, the beam angle of Φ95 horn antenna is 8o, And the horn antenna diameter of 6GHz low frequency pulse radar is Φ246, the beam angle is 15o), the antenna size is small, and the precision is high. 2) The wavelength of 26GHz radar is 11mm, and the wavelength of 6GHz radar is 50mm. When the radar measures the bulk material level, the radar wave reflection mainly comes from the diffuse reflection of the material surface. The intensity of the diffuse reflection is proportional to the size of the material and inversely proportional to the wavelength. The material diameter is much less than 50mm, which is why 26GHz radar is currently the best choice for bulk material level measurement. 3) In some applications of small tanks with small diameters and heights, the length of the 6GHz radar antenna (300-400mm) increases the blind area (about 600mm) invisibly. Due to the poor directivity of the 6GHz radar (large opening angle), the small tanks will produce Multipath reflection; 26GHz radar has high frequency, short antenna and good directivity, which overcomes the shortcomings of 6GHz radar and is suitable for small tank measurement. 4) Due to the harsh on-site environment, over time, the radar antenna will accumulate dirt, water vapor, etc. The 26GHz radar antenna is small, and the addition of a radome can greatly improve the impact of dirt and water vapor; the 6GHz radar antenna is large, and it is difficult to add a radome. And the instrument is heavy and difficult to clean. 5) Due to the good directivity of the 26GHz radar, in many harsh working conditions, the radar can be installed outside the container for measurement through simple isolation.
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