When an electric current flows through any material, the electrons within the current naturally move in a straight line, with the electricity creating its own magnetic field as it charges.
If the electrically-charged material is placed between the poles of a permanent magnet, instead of moving in a straight line, the electrons will instead deviate into a curved path as they move through the material. This happens because their own magnetic field is reacting to the contrasting field of the permanent magnet.
As a result of this new curved movement, more electrons are then present at one side of the electrically-charged material. Through this, a potential difference (or voltage) will then appear across the material at right angles to the magnetic field, from both the permanent magnet and the flow of the electric current.
So, how does a Hall effect sensor work?
Using semiconductors (such as silicon), Hall effect sensors work by measuring the changing voltage when the device is placed in a magnetic field. In other words, once a Hall effect sensor detects that it is now in a magnetic field, it is able to sense the position of objects.
Hall effect sensors and magnets
Magnets are intrinsic to Hall effect sensors, which are activated by the presence of an external magnetic field. The device is then able to sense as an object moves either closer or further away, just through the differing strengths of the magnetic field.
As an example, if a Hall effect sensor was placed in a door frame and a magnet on the door, the sensor would be able to detect when the door is open or closed through the presence of the magnetic field. All magnetic fields have two important characteristics. Firstly, what is called a ‘flux density’, which refers to the amount of magnetic flow passing through a unit area, and secondly, all magnets feature two polarities (the North and South poles).
The output signal that comes out from a Hall effect sensor represents the density of a magnetic field around the device. Hall effect sensors have a preset threshold, and when the magnetic flux density exceeds this limit, the device is able to detect the magnetic field by generating an output called the ‘Hall Voltage’.
Hall effect sensors all have a thin piece of semiconductor material inside them, which passes a continuous electrical current through itself to generate a magnetic field. When the device is placed near an external magnet, the magnetic flux exerts a force on the semiconductor material. This force causes a movement of electrons, creating a measurable Hall voltage and activating the Hall effect sensor.
The output Hall voltage from the Hall effect sensor is directly proportional to the strength of the magnetic field passing through the semiconductor material. Often, this output voltage is quite small - equal to only a few microvolts - with many Hall effect devices including built-in DC amplifiers, alongside logic-switching circuits and voltage regulators, which are there to help improve the sensitivity (and therefore effectiveness) of the device.