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

Float switches are simple, universally applicable and exceptionally reliable. It is not a coincidence that, today, float switches still represent probably the most commonly used principle for level monitoring. But how does a float switch really work?
Float switches, in a straightforward mechanical form, have been completely used 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), due to 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 simple flap control for an irrigation channel, you have implemented a mechanical float switch.
Modern float switches, needless to say, are used for switching a power 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, helpful information 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 aside from each other when a magnetic field is applied. In the case of a float switch with a reed connection with a normally open function, on applying a magnetic field, the leaves are brought into contact. When the contact between your leaves is made, a current 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 Devoted 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 made in every operating state.
Because the contact leaves are under a mechanical preload, a magnetic field should be applied to ensure that the contact leaves close or open in order 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.
How does one specify a float switch?
The following parameters should 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 respected provider of float-based measurement technology solutions, WIKA includes a wide range of variants to meet all your application-specific requirements. Crave are available on the WIKA website. Your contact person will undoubtedly be pleased to advise you on the selection of the correct product solution.

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