Radar level gauge common faults and solutions

1. There is an error in the measured value. The fault shows that the actual liquid level and the measured value change in the same trend, but the values ​​are not equal. This is a common, simpler and easier to eliminate fault. The traditional rope measurement method is used to measure the true sky-space distance. If the measured value is consistent with the distance displayed by the meter, it proves that the quality of the meter itself is not problematic. According to the working principle of the radar level gauge, the actual liquid level is obtained by subtracting the distance D from the measurement reference point to the surface of the medium from the empty tank distance E. Therefore, the empty tank height must be accurate to ensure accurate and reliable measurement. Therefore, before calibration Must be measured in the field to get the most realistic data. If the meter is connected to the computer system, you should also check whether the meter full-scale parameters and computer configuration data are consistent.
2. The measured value is obviously distorted. The fault is represented by the liquid level change and the measured value is constant. When the tank is empty or will be full, the meter will maintain a clear false material level, or it will show that the material in the tank will be full when the tank is full. Go back to a low value. The usual causes of this type of failure are:
(1) Antenna scars. Thick, wet crusting produces a strong reflection of the microwave, keeping the meter's measurements at a constant high level.
(2) When the material is emptied, the antenna or nearby agglomerates generate interference echoes.
(3) When the material is empty, the fixed components in the tank cause strong echo. The following methods should be used to solve the above situation:
(1) Carefully clean the attachments near the antenna and antenna.
(2) Activate and reasonably set the "window resistance" distance. “Window suppression” is also called “near-site suppression”. This function is used to eliminate the influence of mounting flange welds, antennas or nearby materials on the measurement, and is an effective means to optimize the measurement. It sets the near-field suppression distance, and the instrument registers the echoes in this range as interference echoes and does not measure.
(3) Perform "fixed component echo suppression". In addition to intelligently filtering out interference echoes, the radar level gauge can also perform fixed component echo rejection by registering interference waves.
(4) When the material in the tank is full, the meter displays a lower level, which is due to the increase of multiple echoes in the tank. When the program is processed, a long time echo is incorrectly identified as a measurement back. Waves, thus calculating a larger distance over the sky. In this case, the near-field suppression distance should be modified to eliminate the effects of multiple echoes.
3. The measured value fluctuates in the tank due to the undulating surface of the stirring medium, or the temporary interference echo in the tank is enhanced due to the blanking, so that the measured value fluctuates. In addition to improving the application parameters (activating the floating-point average curve algorithm), activating near-field suppression, increasing output damping, you should also check the instrument's mounting position, or consider installing a larger specification antenna.
If it is a two-wire meter powered by a card, you should also check if the DCS analog input card has sufficient load capacity. The 160-slot radar level gauge has experienced a fault in which the measured liquid level is stable but the measured value fluctuates drastically. After thorough inspection, it is determined that the AI ​​cassette load capacity of the DCS system is insufficient. The meter is changed from the card channel power supply to the external power supply mode, and the measurement signal is sent to the card through the isolator, and the instrument fault disappears.
4. The loss of wave fault is manifested by the instrument's “missing wave” error or crash. In the measurement of low dielectric constant liquid, because the liquid's reflective ability is weak, the phenomenon of wave loss often occurs. However, in the alumina industry, there is no problem of weak liquid reflection ability. Therefore, the wave loss is mostly due to vortex and turbulence. The liquid surface, thick and thick foam causes the radar wave to diffuse or be absorbed, so the echo is weak or even echo free. In this case, the application parameters should be set according to the process characteristics in the container. If the above measures have no obvious effect, the installation position or larger size antenna should be changed to enhance the echo intensity. The use of a waveguide or a bypass tube is an effective method for solving the frequent wave loss phenomenon, but the installation work is large and it is not suitable for the easy-to-sludge slurry.
Radar level gauge is one of the most widely used, most accurate and safely maintained liquid level measuring instruments. With the further reduction of the price and the improvement of the cost performance, the application will become more and more extensive and play an increasingly important role in the liquid level measurement. Optimized measurement, first of all should start from the selection, installation and other root sources, and then eliminate the interference measures in use, in order to minimize the probability of instrument failure, truly reflect its reliable, high-precision characteristics, provide for production process control The basis of precision.

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