Briefing of Magnetic level gauge

A magnetic level gauge is a level sensor, that is, a device used to measure the level of a fluid.Magnetic level gauges consist of a "floatable" device that can float in both high and low density fluids.Magnetic level gauges can also be designed for harsh ambient conditions up to 210 bar at 370 °C.

Magnetic level sensors

Magnetic float level sensors involve the use of a permanent magnet sealed within a float, which rises and falls to open or close a mechanical switch through direct contact or proximity to a reed switch.For mechanically actuated floats, the float is directly connected to the microswitch.For magnetic and mechanical float level sensors, chemical compatibility, temperature, specific gravity (density), buoyancy, and viscosity can affect stem and float selection.For example, larger floats can be used for liquids with a specific gravity as low as 0.5 while still maintaining buoyancy.The choice of float material is also influenced by temperature-induced changes in specific gravity and viscosity these changes directly affect buoyancy.

Explanation 

Exploring the physics and engineering behind this design requires studying fundamental magnetism.A standard bar magnet has two poles: a north pole and a south pole.(North reads positive on a gauss meter, south reads negative.)Magnetic fields are drawn using flux lines.The lines are a graphical representation of the magnetic field density.They show the direction of flow of the magnetic field and represent the relative field strength the closer the lines are, the stronger the field. Flux lines will always travel from the north pole to the nearest south pole, and will always leave and enter the surface at 90° or perpendicular to the surface.They can only travel along straight or curved paths, which means they can never change direction suddenly.The flux lines will also always follow the path of least reluctance.Most importantly, they can never cross each other.

Considerations

When selecting a magnetic level gauge it is important to take into account the strength of the magnetic field.The magnetic field is the heart of the magnetic level gauge the stronger the field, the more reliable the instrument will function.Some manufacturers rely on a single magnet for their magnetic level gauges which causes the strength of the north field to be identical to, and as weak as, the south field.It is apparent that at the location of the indicators, switches and transmitters, the field would not be as intense. Some manufacturers use a single annular ring magnet, others use a series of single bar magnets in a circular array in their float design. In this design the relative field strength of the north and south poles will be equal to one another and less than that of a dual magnet design. Moreover, the field strength as you travel around the circumference will have high and low spots as you pass between the individual bar magnets.