Float switch: The facts and so how exactly does it really work?

Float switches are simple, universally applicable and exceptionally reliable. It isn’t a coincidence that, today, float switches still represent the most commonly used principle for level monitoring. But how does a float switch actually work?
Float switches, in a straightforward mechanical form, have been completely 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), 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 with a mechanical lever, e.g. as a straightforward flap control for an irrigation channel, one has implemented a mechanical float switch.
Modern float switches, needless to say, are employed 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 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 when 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 the leaves is made, a current 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, constantly, a normally closed and a normally open contact are simultaneously manufactured in every operating state.
Because pressure gauge 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 required switching signal (monostability). The adjusting collars fitted by the manufacturer serve as a limitation for the float body in the right position, to ensure / keep up with the desired switching signal on reaching the defined filling level.
So how exactly does pressure gauge octa 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 steel, plastic, ?)
Note
As a leading provider of float-based measurement technology solutions, WIKA includes a wide variety of variants to meet 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 selecting the correct product solution.

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