Float switch: What is it and so how exactly does it actually work?

Float switches are simple, universally applicable and exceptionally reliable. It isn’t a coincidence that, today, float switches still represent probably the most commonly used principle for level monitoring. But so how exactly does a float switch really work?
Float switches, in a simple mechanical form, have already been in use for the control of water flows in mills and fields for years and years and today still represent probably the most frequently used technology. A hollow body (float), because of its low density and buoyancy, lifts or drops with the rising and, respectively, falling degree of the liquid. If one uses this movement via a mechanical lever, e.g. as a straightforward flap control for an irrigation channel, one has implemented a mechanical float switch.
Modern float switches, of course, are employed for switching an electric circuit and feature a clearly more sophisticated design. In its simplest form, a float switch includes a hollow float body with a built-in magnet, helpful information tube to guide the float, adjusting collars to limit the travel of the float on the tube and a reed contact located on its inside (see figure).
Figure: Collection of reed contacts of a float switch
How does the float switch function?
Reed contacts (see figure) of a float switch feature contact leaves within the hermetically sealed glass body, which move together or apart from each other when a magnetic field is applied. In the case of a float switch with a reed contact with a normally open function, on applying a magnetic field, the leaves are brought into contact. When the contact between your leaves is made, an ongoing can flow via the closed leaves and a switching signal will be detected.
In the case of a float switch with normally closed switching function, the contact or circuit is interrupted on applying a magnetic field. If one selects a change-over contact, the glass capsule will contain three contact leaves, with which, always, a normally closed and a normally open contact are simultaneously manufactured in every operating state.
Because the contact leaves are under a mechanical preload, a magnetic field should be applied in order that the contact leaves close or open to be able to generate the required switching signal (monostability). The adjusting collars fitted by the manufacturer serve as a limitation for the float body in the right position, to ensure / maintain the desired switching signal on reaching the defined filling level.
How does one specify a float switch?
The following parameters should be defined:
Amount of switch contacts / switching outputs
Position and function of every switching output
Guide tube length
Electrical connection (e.g. Dead )
Process connection
Material (stainless, plastic, ?)
Note
As a respected provider of float-based measurement technology solutions, WIKA has a wide variety of variants to meet all your application-specific requirements. The available products are available on the WIKA website. Your contact person will undoubtedly be pleased to help you on the selection of the appropriate product solution.

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