1. There is an error in the measured value
The faults show that the actual liquid level and the measured value are in the same trend, but the values ​​are not equal. This is a common failure that is simpler and easier to eliminate. The traditional distance measuring method is used to measure the actual distance over the sky. If the measured value is consistent with the distance displayed by the instrument, it is proved that the quality of the instrument itself is no problem. According to the working principle of radar level gauge, the actual liquid level is obtained by subtracting the distance D from the reference point of measurement to the surface of the medium at the distance E of the empty can. Therefore, the height of the empty can must be accurate to ensure accurate and reliable measurement. Therefore, before calibration It must be measured on the ground to obtain the most realistic data. If the instrument is connected to a computer system, check whether the full-scale parameters of the instrument are consistent with the computer configuration data.
2. The measured value is obviously distorted
The fault is manifested as the change of the liquid level and the measured value is always constant. When the tank is empty or nearly full, the meter maintains a clear false material level, or it shows that the material in the tank will bounce back to a low value when the material is full. This type of failure is usually caused by the following reasons:
( 1) Antenna pods. Thick and wet scabs will have a strong reflection of the microwaves, keeping the instrument measurement at a constant high level.
( 2) When the material is drained, the antenna or nearby agglomerates produce interference echoes.
( 3) When the material is empty, the fixed components in the tank cause a strong echo. The following methods should be taken to solve the above situation:
( 1) Carefully clean the antenna and the attachment near the antenna.
( 2) Activate and reasonably set the "window boycott" distance. "Window suppression" is also called "near-field suppression". This function is used to eliminate the impact of mounting flange welds, antenna or its vicinity hanging on the measurement, and is an effective measure to optimize measurement. It sets the near-field suppression distance and the instrument registers echoes in this range as interference echoes without measuring.
( 3) Perform "fixed component echo suppression". In addition to intelligent filtering of interference echoes, radar level gauges can also register fixed wave echoes by registering interference waves.
( 4) The meter displays a lower material level when the material in the tank is full, due to the increase of multiple echoes in the liquid surface elevation tank. When the program is processed, a long echo of a time course is erroneously recognized as the measurement return. Waves to calculate a larger distance over the sky. For this situation, the near-field suppression distance should be modified to eliminate the effects of multiple echoes.
3. Measurement fluctuations
In the tank, the surface of the stirring medium fluctuates violently, or because the lower material causes temporary interference echoes in the tank to increase, so that the measurement value fluctuates. In addition to improving application parameters (floating point average curve algorithm), activating near-site suppression, and increasing output damping, you should also check the installation location of the instrument or consider installing a larger antenna.
According to the author's experience, if the card is powered by a two-wire meter, it should also check whether the DCS analog input card has enough load capacity. The 160-slot radar level gauge for settling has experienced failures in which the measured liquid level is stable but the measured value fluctuates dramatically. After a thorough inspection, it is determined that the AI-cassette load capacity of the DCS system is insufficient. The instrument is changed from the card channel power supply to the external power supply method. The measurement signal is sent to the card through the isolator and the instrument fault disappears.
Loss of wave
The failure manifested as a "lost wave" error or a crash in the instrument . When measuring low-dielectric constant liquids, the phenomenon of loss of waves often occurs because the reflection ability of the liquid is weak, but in the alumina industry, there is no problem of weak liquid reflection ability, so the loss of wave is mostly due to vortices and turbulence. The liquid surface, thick and thick foam makes the radar wave diffuse or be absorbed, so the echo is weak and there is no echo. To treat this situation, the optimal application parameters should be set according to the process characteristics in the vessel. If the above measures have no obvious effect, the installation position or larger antenna should be changed to enhance the echo strength. The use of waveguides or bypass tubes is an effective method to solve the problem of frequent wave losses, but the installation workload is large and it is not suitable for easy slurrying.
Radar level gauge is the most widely used, most accurate measurement, and most convenient maintenance in all types of 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 level measurement. To optimize the measurement, we must start from the root of the selection and installation, and then take better measures to eliminate interference in order to minimize the probability of instrument failure and truly reflect its reliable, high-precision features for the production process. Control provides accurate basis.
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