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About Level Switches
Level switches are meant to monitor the amount of
liquid or bulk material contained in various sizes of vessels like storage
tanks, feeder chutes, stirrers, sluices, etc. Level switches can also
operate as flow control devices or liquid interface indicators. They
can be mounted on vessels or suspended inside of them. Level switch size
varies depending on the type and amount of its mechanisms and the size
of the vessel in which it is operating. A level switch, especially the
common float switch, can look a lot like a “bobber.” Level switch manufacturers
might design their products to have multiple actuation points — each
actuation point looking like a “bob” with a length of thinner connector
in between the points.
Stainless steel, brass and plastic are common materials level switch manufacturers
utilize to construct their product lines of chambered level switches, displacer
level switches, float level switches, liquid level switches, mechanical level
switches and more. The construction of a level switch is dependent upon what
temperature, pressure and type of liquid or material will make up its environment.
Stainless steel is ideal for harsh environments such as high temperatures and
pressures and corrosive conditions. Stainless steel level switches are commonly
used in food processing, medical, and heating and cooling equipment.
Polypropylene and polysulfone, available in different colors, are good choices
for acidic conditions, such as in electroplating and metal cleaning, for lower-temperature
food processing applications and for general-purpose applications in commercial
or consumer appliances and equipment. Brass works in petroleum-based liquids,
such as lubricating oils, gasoline and diesel fuels, and is used in storage tanks
of vehicles, generators, and transmission and hydraulic systems, and in lubrication,
recovery, refining and fuel processing equipment. Level switch manufacturers
can also cater to specific applications, many offering customization.
Level switches can be made to operate with very simple to quite complex sensor
designs. Simple designs might include magnetic features and be triggered by pressure,
temperature or buoyancy. For example, a level switch can be attached to a plastic
tube enabling it to sense the air pressure change as the liquid rises around
and within the tube. Other level switch devices include thermal sensors, vibrating
sensors and optical sensors, which can be modified to recognize specific substances
or to reveal when a certain viscosity, density, opacity or thermal conductivity
condition is reached. Other level switch types include electromechanical and
hydrostatic level switches, ultrasonic level switches, capacitive and conductive
level switches, microwave level switches, and optical and radiometric level switches.
Featured
Articles
http://www.pin-pub.com/pdf/pin/2006/10/pin200610_034.pdf
http://www.sensorsmag.com/sensors/article/articleDetail.jsp?id=328310
Types
- are able
to channel or collect a charge of electricity.
- designs include encasings, or chambers, that
surround the sensor or switch mechanisms. Chambers can beflanged or
sealed to offer protection or hermetic air-tightness.
- devices are affected by buoyancy force changes
on a weight (displacer) heavier than the liquid. Through a spring mechanism,
the suspended weight is attached to an attraction sleeve that moves
into or out of a magnet field, thus actuating or deactuating the switch.
- contain open or closed contacts that indicate
the presence or absence of liquid.
- work with a combination of electric
and mechanical parts.
- mechanisms can most simply
be a rod floating in a liquid that is raised until a pump, an indicator,
an alarm or other
device is activated. It could also be a mercury switch enclosed in
a hinged float, a suspended “bobber” attached to an attraction
sleeve that actuates a magnet field or a more complex sensor construction.
- are sensitive to the static, or stationary,
water pressure acting on them.
- constructions monitor the amount of fluid in a
vessel. Ultra-low liquid level switches are available to detect very
low levels for early indication of a liquid presence and effective
use of expensive liquids.
- designs offer versatility and rugged, industrial
constructions relying on buoyancy principles and made of floats or
displacers, spring mechanisms, attraction sleeves, optional chambers
and magnet fields that activate switching mechanisms.
- are
made up of two separate parts, a transmitter and a receiver. The transmitter
emits a burst of energy at approximately
200 times a second toward the receiver; a substance interruption
of the microwave between the two devices is the trigger.
- can be engineered to provide a number of actuation
points.
- are cost-effective, compact, quickly installable
options that contain no moving parts but use LEDs, which transmit infrared
light, prisms and photo transistors. When a translucent liquid meets
the point where the light contacts the prism, the light is reflected
into the water and does not allow the photo transistor to energize.
- are air-pressure activated through valves
and amplifiers.
- include temperature sensors that provide activation
when a heat change occurs as the liquid surrounds them. Some can sense
the difference between the temperatures of the air space and the liquid.
- devices are designed with a flood-preventing
capability. If liquid reaches the second stage, the switch will turn
the pump off and/or sound an alarm.
- utilize high-frequency (above the audible
level) pulse wave technology.
- can come with reed, probe or tuning fork sensors,
which all have similar constructions of a driver coil that vibrates
a paddle. The switch detects a dampening of the vibration when the
sensor is surrounded by a substance.
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