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Technical Library |
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Liquid Level Sensors |
Liquid level sensors detect the level of substances that flow, including liquids,
slurries, granular materials, and powders. All such substances flow to become essentially
level in their containers (or other physical boundaries) because of gravity. The substance
to be measured can be inside a container or can be in its natural form (e.g. a river or a lake).
The level measurement can be either continuous or point values. Continuous level sensors measure
level within a specified range and determine the exact amount of substance in a certain place,
while point-level sensors only indicate whether the substance is above or below the sensing point.
Generally the latter detect levels that are excessively high or low.
There are many physical and application variables that affect the selection of the optimal
level monitoring method for industrial and commercial processes. The selection criteria
include the physical: phase (liquid, solid or slurry), temperature, pressure or vacuum,
chemistry, dielectric constant of medium, density (specific gravity) of medium, agitation,
acoustical or electrical noise, vibration, mechanical shock, tank or bin size and shape.
Also important are the application constraints: price, accuracy, appearance, response rate,
ease of calibration or programming, physical size and mounting of the instrument, monitoring
or control of continuous or discrete (point) levels.
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Capacitance level sensors excel in sensing the presence of a wide variety of solids, aqueous
and organic liquids, and slurries. The technique is frequently referred to as RF for the radio
frequency signals applied to the capacitance circuit. The sensors can be designed to sense material
with dielectric constants as low as 1.1 (coke and fly ash) and as high as 88 (water) or more.
Sludges and slurries such as dehydrated cake and sewage slurry (dielectric constant approx. 50)
and liquid chemicals such as quicklime (dielectric constant approx. 90) can also be sensed.
Dual-probe capacitance level sensors can also be used to sense the interface between two immiscible
liquids with substantially different dielectric constants, providing a solid state alternative to
the aforementioned magnetic float switch for the “oil-water interface” application.
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Although we try to work with capacitance level sensors whenever possible, there
are many other types of liquid level sensors including vibrating point, rotating paddle,
magnetic and mechanical float, pneumatic, conductive, optical interface, ultrasonic,
microwave/radar, magnetostrictive, resistive chain, hydrostatic pressure, and air bubbler
measurement systems.
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Liquid Level Sensor Information Links
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Liquid Level Sensor Manufacturer Links
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