Level Indicator and Its Uses
Author: SHIR
Level indicators are level measurement devices used to measure the height of liquid or solid in its containing vessel. The two most common types are the magnetic level indicator and the float and board level indicator.
The magnetic level indicator is used to measure fluids and consists of a floatable device that is able to float in high and low density fluids. These indicators can often withstand severe environmental conditions. It comprises a permanent magnet that is sealed within a float, whose rise and fall opens and closes the switch. The most important factor that must be kept in mind while selecting the appropriate magnetic indicator is the magnetic field. The stronger the magnetic field, the more efficient the instrument.
The magnetic indicator is fitted with a precision manufactured float which has internal magnets and flex rings. Moreover, the flag or shuttle type indicator with the stainless steel scale can correctly measure height, volume or percentage of level. These indicators are used in water heaters, industrial boilers, oil/water separators, flash drums, surge tanks, gas chillers, etc.
The float and board level indicators are also used to measure fluid levels in industries. The float is particularly important because of its buoyancy, structural design, volume displacement, etc. A regular float and board indicator would consist of a float, a dustproof pulley housing, pointer cradle with nylon and 150 mm screen printed aluminium scale. These indicators work on the principle of buoyancy. They find application in over ground and overhead storage tanks, and are also used for the measurement of petroleum products like furnace oil, diesel, lube oil, etc. The non-corroding aluminium board with brightly painted scale projects the measurement clearly. This device is easy to handle and also extremely portable.
Some other types of level indicators include:

Tubular
Reflex
Transparent
Welded Pad type
Slight Flow

These devices are very useful for industrial use, and are easily available in the market as well as online. It is, however, important to have full knowledge of the type of matter to be measured and the most appropriate level indicator for it. These indicators are scientifically designed, and resist wear and tear that is likely to take place over time. Level monitoring and automatic movement of fluids is an important concern in most large-scale production units, be it in the health, food or petroleum industry. They are, however, only one part of the larger variety of level measurement instrumentation.

Source: http://www.articlesbase.com/ezine/5683279