FOCUS ON LEVEL MEASUREMENT
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80G radar level meter in foam environment
80G radar level meter is a wide range of FMCW radar level meter applied to solid and liquid level measurement, the antenna emitted microwave to the surface of the measured medium, the microwave frequency is continuously modulated, receive and record the reflected information from the surface of the measured medium, when the emitted signal in the received signal, has changed its emitted frequency, by the associated signal to get a frequency difference, the frequency difference and the surface reflection distance is proportional. The signal processing part analyzes the emitted signal and the echo signal for mixing and processing, and gets the mixed signal spectrum and then the software calculates the distance from the antenna to the surface of the medium, and through the set parameters, the actual level can be calculated. 80G radar level meter as a non-contact level measurement instrument has high accuracy of continuous measurement, wide measurement range, almost independent of the measured medium temperature, pressure, steam, dust and corrosive and toxic harsh conditions, easy to install, easy to install and easy to use. It is easy to install, simple to maintain and operate, and has low failure rate. This makes it the preferred instrument for level measurement in many special occasions.
1. Brief introduction of site working conditions
Ltd., due to the production process of the sewage required to purify the treatment, sewage is dirty, easy to precipitate, the tank is small and has an agitator, and there will be a large amount of foam generated when adding sewage and mixing, the process requires the container to pump negative pressure to lower the boiling point of the sewage, and then collect water vapor condensation. When more foam is added to the defoamer, most of the liquid level meters such as monoflange, static pressure, guided wave radar and float can not be used in this working condition, and only non-contact measuring instruments can be used. Therefore, the tank adopts our non-contact intelligent 80G FM continuous wave radar level meter, which can not only measure the liquid level, but also collect the error information of the radar when there is more sewage foam, and add defoamer through PLC control. However, the level meter is often inaccurate after the start-up of the plant, and it has to be handled 1-2 times almost every day, which has a great impact on the operation of the production plant. In order to solve the problem of high frequency of level meter failures, the causes of the failures are analyzed and corresponding countermeasures are proposed by means of theory and field tests.
2. Fault judgment processing
2.1 Inaccuracy of liquid level meter indication
Phenomenon: The fault is manifested as the measured value is not consistent with the actual level change trend, but there is a fixed error in the value.
Reason: One is the top of the tank plus wire mesh to block the foam, plus the diameter of 100mm round glass to cross the radar electromagnetic wave, the glass surface and radar lens vertical square, resulting in a strong false echo signal. The instrument indication follows the measurement change, which can indicate that the instrument is working normally, due to the complexity of the field conditions causing the measured data fluctuations.
Countermeasures: Understand the measurement method of the orifice height, container height, upper and lower range parameters of the instrument before calibrating the parameters, and make field measurements to obtain the most realistic data when entering the parameters. The wire mesh will be removed after the measurement data is normal, the manufacturer is recommended to install the glass at an angle, the diameter is increased to 150mm, to be fixed installation.
2.2 Liquid level meter indication unchanged
Phenomenon: It shows that the measured value does not match with the actual liquid level at the scene, and it remains unchanged.
Reason: Due to the complex working conditions in the system tank, high temperature water vapor exists from time to time, although the vapor has almost no interference to the radar measurement, but this water vapor condenses into a large number of dense water droplets on the radar lens antenna and glass, resulting in false false radar echoes, reflecting the radar wave, thus affecting the measurement, thus causing the meter output to remain unchanged. Radar level meter loss of wave is also the cause of unchanging instructions, due to the middle of the tank top position is installed in the range mixer, the operation of the liquid level in the tube violent fluctuations, making the radar wave diffusion or absorption, and thus the echo is very little or even no.
Countermeasures: radar lens antenna condensation of water vapor, through the sewage heating, the lens on the water droplets will disappear. Glass tilt installation one can eliminate the false echo signal generated by the glass two is conducive to the downward flow of water beads.
2.3 Level meter indication fluctuations
Phenomenon: The fault is manifested by the existence of violent fluctuations in the measured value, without a specific rule, and does not follow the actual liquid level changes at all.
Reason: The stirrer installed in the top of the tank, when running, the liquid level fluctuates greatly, and occasionally causes media splashing, forming a false liquid level under the radar level meter, so the level fluctuation often occurs when using.
Countermeasures: Firstly, under the condition of ensuring process safety, increase the sampling damping time and inlet and outlet speed of the level meter sensor appropriately to reduce the fluctuation of the level indication caused by false echo. Second, through communication with the user to change the stirring all the time operation to intermittent operation. After using these methods, the processing frequency of the radar level meter was significantly reduced and the level meter worked stably and reliably, which laid the foundation for further technical improvement.
2.4 Other communication to improve the program
Through communication with the user under the condition of not affecting the process, improve the control program, one is to collect the radar level by delaying 2 seconds to compare the participation in the control; two is to report E14 error when the radar detects foam, stop adding water to it, and add water after normal; three is to add defoamer to the sewage when the radar detects foam, do not always add, intermittently.
Through the above summary of field experience, when dealing with radar level meter failure, first of all, should start from the installation of the level meter, site conditions and other root causes, and then take appropriate measures to eliminate interference in use, so as to minimize the chances of failure of the instrument, and truly reflect the advantages of its continuous reliability and high accuracy.