How Hall sensor works? | applied electronics engineering

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How Hall sensor works?

By Applied Electronics - Sunday, April 2, 2017 No Comments
Hall sensors are used to for many purposes such as speed sensors, pressure sensors, switch etc. But they all operate on the basic principle that a magnetic field produces voltage. The presence of magnetic field is required for hall sensors. Any application where magnetic field detection is required can use Hall sensors.

Hall sensors invention is accredited to Dr. Edwin Hall in 1879. He found that when a perpendicular magnetic field is applied on surface of a rectangular gold sheet in which current is flowing from one edge to opposite edge, voltage was developed in the other end of the edges. This voltage is called Hall voltage.

Later with miniaturization of solid state devices and semiconductors it was possible to make small sensing devices entirely as integrated circuit that utilized the Hall effect phenomenon.

Below illustrates a rectangular current carrying sheet(semiconductor). Let I be the current following in the sheet from one side of the edge to the other. Also electrodes is placed such that we can measure the voltage across the other two end edges. In absence of any perpendicular magnetic field the voltage is 0.


Now consider how such simple device can detect presence of magnetic field. Magnetic field is applied perpendicular to the direction of the current flow, that is, perpendicular to the sheet as shown below.


As soon as the magnetic field is near enough the conducting sheet, the field disturbs the current flow and there is voltage drop at the edges perpendicular to the current flow. Unlike in previous case, a certain voltage called Hall voltage is developed.

This Hall voltage is proportional to cross product of current I and the magnetic field density B,





The cross product implies that the voltage direction is perpendicular to the plane of I and B.


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