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Concept
Hall effect sensor
Summary
A Hall effect sensor (or simply Hall sensor) is a type of sensor which detects the presence and magnitude of a magnetic field using the Hall effect. The output voltage of a Hall sensor is directly proportional to the strength of the field. It is named for the American physicist Edwin Hall.
Hall sensors are used for proximity sensing, positioning, speed detection, and current sensing applications. Frequently, a Hall sensor is combined with threshold detection to act as a binary switch. Commonly seen in industrial applications such as the pictured pneumatic cylinder, they are also used in consumer equipment; for example, some computer printers use them to detect missing paper and open covers. Some 3D printers use them to measure filament thickness.
Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing, tachometers and anti-lock braking systems. They are used in brushless DC electric motors to detect the position of the permanent magnet. In the pictured wheel with two equally spaced magnets, the voltage from the sensor peaks twice for each revolution. This arrangement is commonly used to regulate the speed of disk drives.
In a Hall sensor, a current is applied to a thin strip of metal. In the presence of a magnetic field perpendicular to the direction of the current, the charge carriers are deflected by the Lorentz force, producing a difference in electric potential (voltage) between the two sides of the strip. This voltage difference (the Hall voltage) is proportional to the strength of the magnetic field.
Hall effect sensors respond to static (non-changing) magnetic fields. This is a key difference from inductive sensors, which respond only to changes in fields.
Hall sensors are capable of measuring a wide range of magnetic fields, and are sensitive to both the magnitude and orientation of the field. When used as electronic switches, they are less prone to mechanical failure, since there is no wear on physical parts.
Official source
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