Characteristics and causes of "random magnetism" phenomenon in magnetic float level gauge

In the production of chemical and oil refining industries, flow and liquid level are two data that are crucial to production control. Liquid level meters are also the most commonly used instruments in these production sites. Among the many industrial instruments for measuring liquid levels, magnetic float liquid level meters are widely used in oil refining and chemical equipment because of their wide measurement range, low cost, clear indication, high pressure level, good safety and many other advantages. Since the magnetic float uses the principle of magnetic coupling to work and realize liquid level measurement, there is often such a situation that the magnetic float liquid level meter is unstable because of the performance of the magnetic steel. After a period of use, the magnetism weakens, and the magnetic pot in the float and the small magnetic steel in the indicator lose the magnetic connection, resulting in the panel indicator cannot follow the magnetism, and the flap on the indicator cannot be effectively turned over and loses its indication function. Due to the different degrees of weakening of the magnetism of several small magnetic steels in the indicator, the phenomenon of chaotic magnetism (also known as flower screen) is generated. This is the main reason for the chaotic magnetism of early magnetic float liquid level meters.
　　
This situation was more common in the past because the product quality of the raw material supply of the magnetic steel was not up to standard and the general quality was poor. However, with the technological progress and the intensification of market competition in recent years, many enterprises with poor quality have been eliminated or increased their investment in technology and paid attention to product quality. The quality of magnetic steel products on the market has changed greatly. The magnetism of magnetic steel has been enhanced and the magnetic stability has been improved. The "magnetic disorder" phenomenon caused by magnetic steel is quite rare. This article is about another reason that is not easy to detect.
　　
When using a conventional magnetic float level gauge to measure the liquid level of liquefied hydrocarbons that are easily vaporized, the gas phase and liquid phase of the measured medium are transformed into each other in a stable state and reach a balance. At this time, if the liquid is extracted from the tank, the space above the liquid surface increases and the gas phase pressure decreases, a large number of bubbles will be generated in the heating part of the liquid vaporization part. Small bubbles will merge into large bubbles during the rising process. Large bubbles enter the measuring chamber of the conventional magnetic float level gauge, which may cause a rising gas phase segment. When the gas phase segment encounters the float during the rising process, the gas wants to pass around the float. At the same time, the float moves too fast and loses the magnetic connection with the indicator outside the measuring chamber, causing the "magnetic disorder" phenomenon.
　　
In addition, in the closed pipeline of normal production, sometimes due to various reasons, many bubbles of different sizes will be mixed in a certain liquid phase, and even "gas phase" will be produced in severe cases. The appearance of gas phase mixed in these liquid phases will change with the changes in production. If the relative position of the feed pipeline and the liquid level gauge of a device equipped with a conventional magnetic float level gauge is conducive to the entry of bubbles into the liquid level gauge, when the liquid phase mixed with gas phase enters this device, the gas phase will enter the measuring chamber of the magnetic float level gauge. If some dispersed small bubbles enter, the buoyancy of the float will change due to the change in the medium density in the measuring chamber of the magnetic float level gauge, and the position of the float will change, and the liquid level value indicated by the indicator of the magnetic float level gauge will produce a large or small error, that is, this situation interferes with the normal indication of the magnetic float level gauge. If a large bubble or a "gas phase segment" enters the measuring chamber of the magnetic float level gauge, it will also produce the "magnetic disorder" phenomenon described above when liquefied hydrocarbons are not handled.
 
The above phenomena that cause conventional magnetic float level gauges to fail to work properly are all caused by the impact of the gas phase mixed in the liquid phase medium measured by the level gauge on the level gauge. In order to make the magnetic float level gauge work properly, it must be modified to adapt to this impact.
 
Supplementary analysis: The magnetic float level gauge is a fixed buoyancy level gauge, which measures the interface between the lower liquid phase medium and the upper gas phase. When the pressure change in the container causes the medium to change phase, this interface will fluctuate. For example, a large number of bubbles are generated in the medium during decompression, which lifts the gas-liquid interface. This phenomenon is different in the bypass pipe and the inside of the container, so it may be eliminated in another way.

Fundamentally speaking, the fixed buoyancy level gauge has no ability to overcome the false liquid level caused by phase change. Because it only recognizes the gas-liquid interface, it does not ask how much is in the tank. The sinking barrel level gauge and the differential pressure level gauge are fundamentally to measure the weight of the medium in the container and calculate the liquid level data in the tank through pressure. However, the latter two types of liquid levels also have disadvantages, that is, although the instrument shows that the liquid level is not full, it is actually overflowing. Therefore, the specific selection of liquid level meter in production requires comprehensive consideration of various factors. In order to ensure the correct liquid level, many companies even use two liquid level meters at the same time to monitor the change of liquid level to ensure the safety and stability of production operation.