Sensors

Magnetic sensors detect a varying field in an airgap using a Hall effect or magnetoresistance probe which delivers a voltage depending on B. Magnetic position and speed sensors used in brushless motors and automobile system controls offer reliable noncontact sensing in a hostile environment involving dirt, vibration and high temperatures. 
The point to emphasize here is that a permanent magnet usually forms part of the circuit; it provides a noiseless magnetic field with no expenditure of energy. For example, a variable reluctance sensor with a magnet and a Hall probe may be used to detect the rotation of a toothed wheel.

مواضيع ذات صلة

عجائب المجالات المغناطيسية

المجال المغناطيسي الارضي

Planetary magnetism

Therapy and treatment

Cellular biology

Magnetotaxis

Magnetic field effects

Electrodeposition

Magnetic memory

Materials for spin electronics

Actuators

Switchable magnets; holding magnets