Float switch: The facts and how does it actually work?

Float switches are simple, universally applicable and exceptionally reliable. It is not a coincidence that, today, float switches still represent probably the most frequently used principle for level monitoring. But how does a float switch really work?
Float switches, in a straightforward mechanical form, have been completely in use for the control of water flows in mills and fields for years and years now still represent the most commonly used technology. A hollow body (float), because of its low density and buoyancy, lifts or drops with the rising and, respectively, falling level of the liquid. If one uses this movement via a mechanical lever, e.g. as a simple 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 show a clearly more sophisticated design. In its simplest form, a float switch consists of a hollow float body with a built-in magnet, a guide tube to steer the float, adjusting collars to limit the travel of the float on the tube and a reed contact situated on its inside (see figure).
Figure: Selection 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 whenever a magnetic field is applied. Regarding a float switch with a reed contact with a normally open function, on applying a magnetic field, the leaves are brought into contact. Once the contact between your leaves is made, an ongoing can flow via the closed leaves and a switching signal will be detected.
Regarding 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, all the time, a normally closed and a normally open contact are simultaneously manufactured in every operating state.
Since Conscientious are under a mechanical preload, a magnetic field should be applied in order that the contact leaves close or open as a way to generate the desired switching signal (monostability). The adjusting collars fitted by the product manufacturer serve as a limitation for the float body in the correct position, to make sure / keep up with the desired switching signal on achieving the defined filling level.
So how exactly does one specify a float switch?
The following parameters ought to be defined:
Number of switch contacts / switching outputs
Position and function of every switching output
Guide tube length
Electrical connection (e.g. PVC cable outlet)
Process connection
Material (stainless steel, plastic, ?)
Note
As a leading provider of float-based measurement technology solutions, WIKA has a wide variety of variants to meet up all your application-specific requirements. The available products are available on the WIKA website. Your contact person will undoubtedly be pleased to advise you on the selection of the appropriate product solution.

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