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 how does a float switch actually 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 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 level of the liquid. If one uses this movement with a mechanical lever, e.g. as a simple flap control for an irrigation channel, one has implemented a mechanical float switch.
Modern float switches, needless to say, are employed for switching an electric circuit and feature a clearly more sophisticated design. In its simplest form, a float switch includes a hollow float body with an integral magnet, a guide tube to steer 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 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.
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, always, a normally closed and a normally open contact are simultaneously made in every operating state.
Since Supercharge are under a mechanical preload, a magnetic field must be applied to ensure that the contact leaves close or open as a way 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 make sure / maintain the desired switching signal on reaching the defined filling level.
How does one specify a float switch?
The following parameters ought to be defined:
Number 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 of your application-specific requirements. The available products are available on the WIKA website. Your contact person will undoubtedly be pleased to help you on selecting the correct product solution.