Proximity switch with magnetic field-sensitive sensor

A method for constructing a proximity switch, comprising the steps of:

• forming a U-shaped permanent magnet with a vertical direction of magnetization with a plastic-bonded permanent magnet powder, the U-shaped permanent magnet having a magnetic flux-free region between limbs of the U-shaped magnet caused by three like mutually repelling poles of the U-shaped permanent magnet, said flux-free region having a longitudinal extent substantially perpendicular to a magnetic pole axis of each of said limbs;
• providing a magnetic field-sensitive sensor and positioning said magnetic field-sensitive sensor in said magnetic flux-free region between said limbs and inwardly of terminating ends of said limbs by encapsulating the U-shaped permanent magnet and the magnetic field-sensitive sensor in a housing;
• and
• dimensioning said housing such that a flat ferromagnetic triggering part can be brought close above said limbs of the U-shaped magnet in a plane parallel to a base of the U-shaped magnet so that a switching signal is triggered from the sensor by cancellation of the magnetic flux-free region when the triggering part is brought close to poles of said limbs of the U-shaped magnet, the switching signal being capable of evaluation to indicate activation of the proximity switch.

A proximity switch system, comprising:

• a U-shaped permanent magnet with a vertical direction of magnetization, said permanent magnet defining a magnetic flux-free region formed by three like mutually repelling poles and positioned between limbs of the U-shaped magnet, a first of the like poles being in a base of the U-shaped magnet between the limbs and second and third ones of the like poles being at ends of said limbs, said flux-free region having a longitudinal extent substantially perpendicular to a magnetic pole axis of each of said limbs;
• a magnetic field-sensitive sensor positioned in said magnetic flux-free region between said limbs and inwardly of terminating ends of said limbs;
• a housing encapsulating the permanent magnet and the sensor and positioning the sensor relative to the magnet;
• a flat ferromagnetic triggering part positionable closely above said limbs of the U-shaped magnet in a plane parallel to the base of the U-shaped magnet;
• and
• a switching signal triggered from the sensor by cancellation of the magnetic flux-free region when the triggering part is brought close to poles of said limbs of the U-shaped magnet, the switching signal being capable of evaluation to indicate activation of the proximity switch.