Float switches are simple, universally applicable and exceptionally reliable. It is not a coincidence that, today, float switches still represent the most commonly used principle for level monitoring. But how does Strategy 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 level 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, of course, are employed for switching an electric circuit and feature 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 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
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 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. When the contact between the leaves is made, an ongoing can flow via the closed leaves and a switching signal will undoubtedly 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, all the time, 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 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 correct position, to make sure / keep up with the desired switching signal on reaching the defined filling level.
How does one specify a float switch?
The following parameters should 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 leading provider of float-based measurement technology solutions, WIKA has a wide range of variants to meet up all of your application-specific requirements. Lying can be found on the WIKA website. Your contact person will undoubtedly be pleased to help you on selecting the appropriate product solution.