Level Measurement

What is a magnetic level indicator?

A magnetic level indicator can provide accurate level measurement, it can provide a high clarity indication of the liquid level. A magnetic level indicator consists of three major components and they are float chamber, float, and indicator system. A magnetic level indicator is principally designed as an alternative to glass level gauges. So the magnetic level indicator is a replacement for the glass level gauges. The magnetic level gauges have visual level indication but it is not categorized as direct level measurement, it is due to the level indication method the level indication is done according to the magnetic attraction between the internal float and the external indicator. This level measurement device is very reliable when properly maintained.

What are the factors that must be considered while selecting a magnetic level indicator?

The strength of the magnetic coupling between the float and the indicator must be directly proportional to the distance separating them. We must not allow any dirt or debris in the chamber, it can be lodged between the float and the inner wall, and it could prevent the float from following the change in the liquid level so the measurement will be badly affected. The magnetic level indicator is designed for specific liquid density so if the float is not properly manufactured or the density of the process fluid changes then there will be an error in the measurement. We must not use the magnetic level indicator for the process fluid that has less specific gravity than that of the float.

The magnetic level indicator must be made of stainless steel or other materials that could be compatible with the process fluid. The float must be selected according to the density of the liquid. The length of the magnetic level indicator must be suitable for the level range of the application. It must not be used for the liquid-liquid interface. We must make sure that the float and the chamber are designed according to the design pressure and temperature.

How does a magnetic level indicator work?

In a magnetic level, indicator floats are used to indicate the level, this type of level measurement is done with the attraction between two magnets. This device has a magnet that is enclosed in a float and it also has a second magnet which is called the magnet follower and it is in a non-ferrous metal tube. The magnet in the float attracts the magnet in the tube as the float raises and lowers with the level of the process liquid and this would cause the magnet inside the tube to raise and lower. By checking the position of the magnet the level of the liquid in the tank can be determined.

How to install a magnetic level indicator?

The effective pressure of the installation should not be more than the maximum permitted pressure of the instrument nameplate. The chamber cage level indicator must be installed vertically on the vessel. We must make sure that any magnetic field that is generated by other equipment does not affect the measurement. The bolts and gaskets that are selected must be suitable for the pressure rating of the connecting flange and the operating pressure. The process connections must be fit properly. In order to do the level measurement, the chamber material should be a non-magnetic type.

What are the advantages of magnetic level indicator?

  • It is cheap
  • Easy to install
  • High accuracy
  • It is not affected by material characteristics such as conductivity and dielectric constant

What are the disadvantages of the magnetic level indicator?

  • It would require recalibration if the liquid density changes
  • There is a chance for foreign material build-up on the float
  • It cannot be used for liquids containing magnetic particles
  • It is only suitable for the liquids that have specific gravity more than that of the float
  • The depth of the immersion of the float would increase as the product density decreases, the depth is also dependent on the float material
  • The float requires thick walls to operate at higher temperatures

What are the applications of magnetic level indicator?

  • Power stations
  • Chemical industry, petro-chemistry,& offshore
  • Environmental industry
  • Food and beverage industry
  • Shipbuilding, engineering
  • Pharmacy & water purification
  • Waste treatment

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