Magnetic Sensors
As with inductive proximity sensors, magnetic proximity sensors also have an LC oscillating circuit, a signal evaluator, and a switching amplifier. They also have a core (strip) made of amorphous, highly permeable, and magnetically soft glass-metal.
This strip attenuates the oscillating circuit using eddy-current losses. The core becomes magnetically saturated very quickly if a magnetic field is applied, e.g. if a magnet is brought closer. The eddy-current losses attenuating the oscillating circuit are reduced and the oscillating de-attenuates. The power consumption of a magnetic proximity sensor therefore increases as a magnet is brought closer, in contrast to inductive proximity sensors where the oscillator current is reduced as the switching trigger is brought closer. For this reason, the starting curves are not the lines of an electro-magnetic field, but limit lines which describe the saturation of the glass-metal strip by a magnet and the associated switch-through of the sensor.
A major advantage of this technology is that large sensing ranges are possible even with small sensor types.
Permanent magnets are usually used to trigger magnetic proximity sensors. They comprise magnetically hard substances - steel alloyed with other metals such as aluminium, cobalt, and nickel. Magnetically hard ferrite with similar properties can be also be produced from compounds containing iron oxide and other metal oxides.
