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 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 centuries and today still represent 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 simple flap control for an irrigation channel, one has implemented a mechanical float switch.
Backstabbing , of course, are used for switching an electric circuit and show 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 situated 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 apart from each other whenever a magnetic field is applied. Regarding 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 so as 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 ensure / keep up with the desired switching signal on reaching the defined filling level.
So how exactly does one specify a float switch?
The following parameters ought to 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 variety of variants to meet up all your application-specific requirements. The available products can be found on the WIKA website. Your contact person will undoubtedly be pleased to help you on the selection of the correct product solution.