Hall Effect and Magnetic Position Sensors

The Hall effect describes the appearance of a transverse voltage across a current-carrying conductor or semiconductor when it is placed in a magnetic field perpendicular to the current. The moving charge carriers are deflected toward one edge of the material, producing a measurable Hall voltage that is proportional to the magnetic flux density. Edwin Hall first observed this phenomenon in 1879, and modern sensors usually exploit it in thin semiconductor films where the effect is strong enough to be useful.

Hall effect sensors are widely used for contactless detection because they respond to a magnetic field rather than to mechanical contact. Linear Hall devices give an output that tracks field strength, while switching types contain a comparator that produces a digital output once the field crosses a threshold. Typical applications include brushless DC motor commutation, rotary and linear position sensing, current measurement (where the field around a conductor is sensed), proximity detection and speed measurement using a toothed wheel and a magnet.

Other magnetic field sensors share the same goal but use different physics. Anisotropic magnetoresistive (AMR) sensors rely on the change in electrical resistance of a ferromagnetic film, such as permalloy, when its magnetisation rotates relative to the current direction. These devices are more sensitive to weak fields than basic Hall elements and are common in compassing and angle measurement. The choice between Hall and magnetoresistive technologies depends on field strength, required accuracy, temperature range and cost.

Frequently asked questions

What does a Hall effect sensor actually measure?

It measures magnetic flux density. The Hall voltage produced is proportional to the component of the magnetic field perpendicular to the sensing element.

Why are Hall sensors preferred for position sensing?

They are contactless, so there is no mechanical wear, and they tolerate dust, dirt and non-magnetic barriers between the magnet and the sensor.

How does a magnetoresistive sensor differ from a Hall sensor?

A magnetoresistive sensor detects field through a change in resistance of a ferromagnetic film, giving higher sensitivity to weak fields than a typical Hall element.