Usually metallic, tanks can be a fairly broad category including 30 gallon and 55 gallon drums as well as most other types of large containers such as hoppers or bins.
Tank level indicators are fairly versatile types of level switches and can be used in diverse applications and industries, including petroleum, for level control of oil and gas in refineries; industrial manufacturing, for measurement of the levels of various processing media; chemical processing, for preventative level control of potentially hazardous materials; marine, used in the measurement of marine vessel fluid levels; and residential, for a variety of level indicating applications.
Tank level indicators can be used not only in above ground tanks, such as overhead tanks or grounded tanks, but they can also be used for level control in underground tanks as well. Due to the diversity of the capabilities of tank level indicators, additional industries that utilize them include defense contracting, commercial, private sector aircraft manufacturing, agriculture and wastewater treatment.
Tank level indicators function mainly to measure the level of various materials based on the principle of differential pressure. This means that the level indicator is able to determine the level of the material due to the difference between the two pressures (the pressure at the bottom of the tank compared to the atmospheric pressure) being equal to the height of the material when it is multiplied by the specific gravity of the material.
As a result, as long as the gravity of the material (or the density) remains the same, then the tank level indicator will be able to accurately measure the level of the material. When level measurement is based upon this principle, it is also commonly referred to as hydrostatic tank gauging (HTG). Floating level indicators are often a popular form of tank level indicators, and continuous level floats are one of the most accurate ways of measurement control in tanks.
A continuous level float functions by means a sensors (which can range anywhere from two to 25 ft in length) is inserted at the top of the tank through either a flanged, welded or screwed connection. The accuracy of level measurement using this type of device is approximately up to .02 in. and as a result is used in many applications requiring high precision in measurement.