Radar level meter is used to measure the level of non-contact sensor instrument, suitable for liquid storage tank, solid silo, process container or strong dust easy crystallization, condensation occasions.It has the advantages of low maintenance, high performance, high precision, high reliability and long service life.Can adapt to high temperature, high pressure, steam and other harsh production environment.

    Radar level meter has the advantages of maintenance-free, no impact and wear, no hanging phenomenon, no parts replacement problem, long service life, and simple installation, simple calibration, also not affected by the bin gas composition, dust, temperature changes, etc., in the field of actual level measurement has been widely used.

1、Working principle of radar level meter

    Radar level meter is the use of UHF electromagnetic wave through the antenna to be detected by the container of the material surface, when the electromagnetic wave meets the material surface reflected back, the sensor detects the transmission and echo time difference, so as to calculate the height of the material surface. The better the electrical conductivity or dielectric constant of the measured medium is, the better the reflection effect of the echo signal is. Radar sensors use special time interval adjustment technology to amplify and locate the echo signal per second, and then analyze and process it. Therefore, radar level sensor can carefully analyze and process these amplified echo signals within 0.1s, without spending a lot of time to analyze the frequency.

    Radar level meter is mainly composed of transmitting and receiving device, signal processor, antenna, operation panel, display and so on. Transmitting  reflecting receiving is the basic principle of radar level meter. It is divided into time difference type and frequency difference type.

    The time difference type is the transmission frequency is fixed, by measuring the transmission wave and reflection wave running time, and through the intelligent signal processor, to measure the height of the measured material level. The relation between the running time of the radar level gauge and the level distance is t=2d/ C. Where C is the propagation speed of electromagnetic waves, C=3×10⁸m/s; D is the distance m between the material level of the measured medium and the probe; T is the time s of the probe from transmitting electromagnetic wave to receiving reflected electromagnetic wave.

    The frequency difference formula is to measure the frequency difference between the transmitted wave and the reflected wave, and convert this frequency difference into an electrical signal proportional to the measured liquid level. The transmitter frequency of this level meter is not a fixed frequency, but a first amplitude adjustable frequency.

2、Characteristics of radar level meter

    Radar level meter in inflammable, explosive, corrosive, high temperature, viscous and other harsh measurement conditions, but also shows its performance, especially suitable for large vertical tank and spherical tank measurement. The understanding of its performance is conducive to the correct application of radar level meter.

3、Selection of radar level meter

3.1 The radar level meter is selected according to the measured medium

   • The measured medium is liquid, which can be met by all radar products. For small range storage tanks, the 80GHz radar level gauge is recommended.

   • The medium to be measured is solid small particles/powder, or small range bin. It is recommended to use 80GHz radar level meter.

3.2 Select radar level meter according to antenna shape

   • Antenna is a key component of radar level gauge. The shape of antenna determines the focus and sensitivity of radar wave.

   • The flared antenna is suitable for most occasions and has excellent focusing characteristics. This type of antenna is used in many liquid storage tanks or solid silos in the field, but is not suitable for measuring corrosive media.

   • The mounting flange of the rod antenna is small in size, good in chemical stability, easy to clean, insensitive to the adhesion of condensed water, especially suitable for high-precision measurement of corrosive media (such as sulfur) and narrow installation tube.

   • Flanged down-mounted antenna is suitable for high temperature media, corrosive media or cannot be mounted on top of the environment.

   • Parabolic antenna has good focusing ability and is not affected by heating steam. It is especially suitable for measuring in tanks of large vessels with heating steam, such as residuum, asphalt, etc. The measuring range can be up to 40m.

   • 80G radar generally adopts spherical antenna and has strong signal collection capability.

4、 radar level meter installation notes

   • As far as possible to avoid installed in the launch Angle of false reflection devices, such as limit switches, temperature sensors, etc. In particular, obstacles should be avoided in the 1/3 cone transmitting zone closest to the antenna (because the closer the barrier, the stronger the false reflection).If it is unavoidable, it is recommended to use a refractor plate to refract the false reflected signal that is too strong. In this way, the energy density of the false echo can be reduced and the false signal can be filtered out easily by the sensor.

   • Do not install above the inlet to avoid false reflection.

   • The sensor should not be installed in the center of the arch tank (otherwise the sensor will receive false echo enhancement), nor should it be installed very close to the tank wall. The distance between the inner wall of the tank and the outer wall of the short tube should be greater than 1/6 of the diameter of the tank.

   • Do not install the sensor where there is strong eddy current. For example, due to stirring or strong chemical reaction, it is recommended to use wave guide tube or bypass pipe installation.

   • If the sensor is installed on the nozzles, the antenna must extend out of the nozzles, and the flared antenna should extend out of the nozzles at least 10mm.If the trumpet length is shorter than the short tube, the antenna extension tube should be used. Rod antenna pipe length and diameter should be carried out according to the product requirements of different manufacturers, rod antenna must be extended to install short tube.

    About the waveguide tube: the inner wall of the waveguide tube must be smooth and uniform in diameter. No welding shall be allowed. No 0.1mm weld shall be produced in any transition section. The Angle between two rows of conducting grooves is 180° (not 90°);The width or aperture of the guide wave groove is 1/10 of the diameter of the tube. The number and length of the guide wave groove will not affect the measurement. The spacing between the two holes is 15cm...50cm, the bottom opening of the wave guide tube must be at the minimum level required for measurement in the pipeline.

5、 Problems and solutions in the application of radar level gauge

    Instrument seal: cable inlet and instrument cover seal is not strict enough to lead to rain water or other liquid, dust, wet gas into the instrument, causing the instrument circuit part failure. Therefore, the sealing joint must be fixed, and it must be installed well. If necessary, the protective cover can be fixed. It is a good method to wrap the whole meter.

    The treatment of antenna scarring: the hanging material with very small dielectric constant has no effect on the measurement in the dry state, while the hanging material with very high dielectric constant has an effect on the measurement. It can be purged with compressed air (or rinsed with water), and the cooled compressed air reduces the temperature of the flange and electrical components. Scarring can also be cleaned periodically with an acidic cleaning solution, but measurements cannot be taken during cleaning.

    Therefore, only after a detailed understanding of the measured object and its container technical parameters, according to the actual situation of the site to choose the appropriate radar level meter, radar level meter can be long-term, reliable operation.