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

Float switches are simple, universally applicable and exceptionally reliable. It isn’t a coincidence that, today, float switches still represent the most frequently used principle for level monitoring. But so how exactly does a float switch really work?
Float switches, in a simple mechanical form, have been in use for the control of water flows in mills and fields for centuries now still represent probably the most frequently 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, one has implemented a mechanical float switch.
Modern float switches, of course, are used 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 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 situated on its inside (see figure).
Figure: Collection of reed contacts of a float switch
How does the float switch function?
ไดอะแฟรม ซีล (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. 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. Once 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, constantly, 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 must be applied in order 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 / maintain the desired switching signal on achieving the defined filling level.
How does ไดอะแฟรม specify a float switch?
The following parameters should be defined:
Amount of switch contacts / switching outputs
Position and function of each switching output
Guide tube length
Electrical connection (e.g. PVC cable outlet)
Process connection
Material (stainless, plastic, ?)
Note
As a leading provider of float-based measurement technology solutions, WIKA has a wide variety of variants to meet all of your application-specific requirements. The available products are available on the WIKA website. Your contact person will be pleased to help you on the selection of the appropriate product solution.

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