Hall Effect Sensor

A Hall effectsensor is a transducer that varies its output voltage in response to a magneticfield. Halleffect sensors are used for proximity switching, positioning, speed detection, and currentsensing applications.

In a Hall effect sensor, a thin strip ofmetal has a current applied along it. In the presence of a magnetic field, theelectrons in the metal strip are deflected toward one edge, producing a voltagegradient across the short side of the strip (perpendicular to the feed current).Hall effect sensors have an advantage over inductivesensors in that, while inductive sensors respond to a changingmagnetic field which induces current in a coil of wire and produces voltage atits output, Hall effect sensors can detect static (non-changing) magneticfields.

In its simplest form, the sensor operatesas an analog transducer, directly returning a voltage. With a knownmagnetic field, its distance from the Hall plate can be determined. Usinggroups of sensors, the relative position of the magnet can be deduced.

Frequently, a Hall sensor is combined withthreshold detection so that it acts as and is called a switch. Commonly seen in industrial applications such as thepictured pneumaticcylinder, they are also used in consumer equipment;for example some computerprinters use them to detect missing paper and open covers. Theycan also be used in computerkeyboards applications that require ultra-high reliability.

Hall sensors are commonly used to time thespeed of wheels and shafts, such as for internalcombustion engine ignitiontiming, tachometers and anti-lockbraking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. In thepictured wheel with two equally spaced magnets, the voltage from the sensorwill peak twice for each revolution. This arrangement is commonly used toregulate the speed of disk drives.