Working principle and application scope of balanced flowmeter radar level meter

The guided wave radar level meter of the balance flow meter is a microwave level meter, which is an application of microwave (radar) positioning technology. It transmits energy waves through a device that can transmit energy waves (generally pulse signals). The energy waves are transmitted in the waveguide. The energy waves are reflected by obstacles. The reflected energy waves are transmitted by the waveguide to the receiving device, and then the receiving device receives the reflected signal. The level change is determined by measuring the time difference of the energy wave movement process. The microwave signal is processed by an electronic device and finally converted into an electrical signal related to the level.

The energy radiation level is low. The energy wave used by this device is a pulse energy wave (the frequency is generally lower than that of the intelligent radar level meter). The maximum pulse energy of a general pulse energy wave is about 1mW (the average power is about 1μW), which will not cause radiation damage to other equipment and personnel.

2. Scope of application and characteristics:

The guided wave microwave level meter is used for contact and continuous measurement of liquids, slurries, granular materials and other media with relatively small dielectric constants. It is suitable for occasions with large temperature and pressure changes and the presence of inert gas or steam.

(1) The radar level meter adopts an integrated design with no moving parts, no mechanical wear and long service life.

(2) The electromagnetic waves emitted by the radar level meter during measurement can pass through a vacuum, do not require a transmission medium, and are not affected by the atmosphere, steam, or volatile mist in the tank. They can be used to measure the level of volatile media such as crude benzene.

(3) Radar level meters can be used to measure the level of almost all liquids. When electromagnetic waves are reflected on the liquid surface, the signal will attenuate. When the signal attenuation is too small, the radar level meter will not be able to measure enough electromagnetic wave signals. Conductive media can reflect electromagnetic waves very well. For MAT radar level meters, even slightly conductive materials can reflect enough electromagnetic waves. Non-conductive media with a dielectric constant greater than 1.5 (the dielectric constant of air is 1.0) can also ensure sufficient reflected waves. The larger the dielectric constant, the stronger the reflected signal. In practical applications, almost all media can reflect enough reflected waves.

(4) Non-contact measurement is adopted and is not affected by the density, concentration and other physical properties of the liquid in the tank.

(5) The measuring range is large, with the maximum measuring range reaching 0~35m, which can be used for high temperature and high pressure liquid level measurement.

(6) The key components such as the antenna are made of high-quality materials with strong corrosion resistance and can adapt to highly corrosive environments.

(7) Rich in functions, it has a false wave learning function. By inputting the actual liquid level, the software can automatically identify the false echoes from the liquid surface to the antenna and eliminate the interference of these waves.

(8) Parameters are easy to set. They can be set using the simple operation keys on the level meter, or they can be set remotely or directly connected to the communication end of the level meter using a HART protocol handheld operator or a PC equipped with MAT software. It is very convenient.

Principle of MAT radar level meter

The radar level meter adopts the transmission-reflection-reception working mode. The antenna of the radar level meter transmits electromagnetic waves, which are reflected by the surface of the measured object and then received by the antenna. The time from the emission to the reception of the electromagnetic wave is proportional to the distance to the liquid surface. The relationship is as follows:

D=CT/2

Where D is the distance from the radar level meter to the liquid surface; C is the speed of light; T is the running time of the electromagnetic wave.

The radar level meter records the time taken by the pulse wave, and the transmission speed of the electromagnetic wave is a constant, so the distance from the liquid surface to the radar antenna can be calculated, thereby knowing the liquid level.

3. Precautions for installing radar level meter

Whether the radar level meter can measure accurately depends on the signal of the reflected wave. If the liquid surface cannot reflect the electromagnetic wave back to the radar antenna at the selected installation location or there are interference objects within the range of the signal wave that reflect interference waves to the radar level meter, the radar level meter cannot accurately reflect the actual liquid level. Therefore, it is very important for the radar level meter to reasonably choose the installation location. The following points should be noted during installation:

(1) The axis of the radar level meter antenna should be perpendicular to the reflecting surface of the liquid level.

(2) If the stirring valve in the tank, the adhesion of the tank wall and the path and other objects are within the signal range of the radar level meter, they will produce interfering reflected waves and affect the liquid level measurement. When installing, choose a suitable installation location to avoid interference from these factors.

(3) The horn of the horn-type radar level meter must exceed the inner surface of the mounting hole by a certain distance (>10mm). The antenna of the rod-type level meter must extend out of the mounting hole, and the length of the mounting hole cannot exceed 100mm. For circular or elliptical containers, it should be installed at a distance of 1/2R (R is the radius of the container) from the center, and should not be installed in the center of the top of the circular or elliptical container, otherwise the radar wave will be reflected multiple times by the container wall and converge at the center of the container top, forming a strong interference wave, which will affect the correct measurement.

　 (4) For liquid level measurement of containers with large liquid level fluctuations, a liquid level meter with a bypass pipe can be used to reduce the impact of liquid level fluctuations.

After installation, you can use a PC with MAT software to observe the reflected wave curve to determine whether the level meter is installed properly. If not, further adjust the installation position until it is satisfactory.

In our company's storage tank, we initially chose to install the radar level meter at a position about 300mm away from the tank wall. The reflected wave curve observed by PC is shown in Figure 2a. There is a strong interference wave in front of the reflected wave. The main reason for this interference wave may be the scale on the tank wall. To avoid the influence of these factors, we chose to install the radar level meter at a position 1000mm away from the antenna and the support column as shown in Figure 1b. The reflected wave curve observed by PC equipped with MAT software is shown in Figure 2b, which reduces the intensity of the interference wave and effectively eliminates the influence of the interference wave.

For interference waves that cannot be avoided in some installation locations, such as interference waves in Figure 2b, the MAT radar level meter can also use its function of identifying false waves. The level meter can identify interference reflection waves according to the actual liquid level and store them in the internal database of the radar level meter, so that the radar level meter can identify these interference waves during data processing, remove the influence of these interference reflection waves, and ensure the accuracy of measurement.

4. Maintenance of radar level meter

The radar level meter is mainly composed of electronic components and antennas, with no moving parts, and rarely fails in use. An occasional problem encountered in use is that some volatile organic matter in the storage tank will crystallize on the bell or antenna of the radar level meter. For these, they only need to be checked and cleaned regularly, and the maintenance is minimal.

In daily maintenance, you can use a PC (with MAT software) to remotely observe the reflected wave curve. For new interference waves that may be generated later, you can use the level meter's ability to identify false waves to remove the influence of these interfering reflected waves and balance the flow meter to ensure correct measurement.