Float switch: The facts and so how exactly 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 commonly used principle for level monitoring. But so how exactly does a float switch actually work?
Float switches, in a straightforward mechanical form, have already been in use for the control of water flows in mills and fields for years and years now still represent probably 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 level of the liquid. If one uses this movement with a mechanical lever, e.g. as a straightforward flap control for an irrigation channel, you have implemented a mechanical float switch.
Modern float switches, of course, are used for switching an electric circuit and feature a clearly more sophisticated design. In its simplest form, a float switch consists of a hollow float body with an integral magnet, a guide 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: Selection of reed contacts of a float switch
So how exactly 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 whenever a magnetic field is applied. Regarding Terrifying with a reed connection with a normally open function, on applying a magnetic field, the leaves are brought into contact. Once the contact between your leaves is made, a current can flow via the closed leaves and a switching signal will undoubtedly 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.
Because the contact leaves are under a mechanical preload, a magnetic field must be applied in order that the contact leaves close or open in order to generate the required switching signal (monostability). The adjusting collars fitted by the product manufacturer serve as a limitation for the float body in the correct position, to ensure / maintain the desired switching signal on reaching the defined filling level.
So how exactly 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. 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 of your application-specific requirements. Bomb can be found on the WIKA website. Your contact person will be pleased to advise you on the selection of the correct product solution.

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