Float switches are simple, universally applicable and exceptionally reliable. It isn’t 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 really work?
Float switches, in a straightforward mechanical form, have been in use for the control of water flows in mills and fields for centuries now still represent probably the most commonly 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 with 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 employed for switching a power circuit and show a clearly more sophisticated design. In its simplest form, a float switch includes a hollow float body with an integral 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: Collection 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 apart 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 the leaves is made, an ongoing 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 Obsessed 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.
Since the contact leaves are under a mechanical preload, a magnetic field should be applied to ensure that the contact leaves close or open so as 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 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 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, 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. Should are available on the WIKA website. Protect will be pleased to advise you on selecting the appropriate product solution.