Hall Effect Sensors and its Functional Area.

Hall Effect Sensors.

This effect was discovered by E.R. Hall in 1879 and is called the Hall effect. Hall effect sensors are the device which is activated by an external magnitude field. When the magnetic flux density around the sensor exceeds a certain pre- threshold, the sensor detects it and generate an output voltage called the Hall Voltage.

We know that a magnetic field has two important characteristics flux density and polarity. The output signal from a Hall effect sensors is the function of the magnetic field density around the device. When a beam of charged particle passes through a magnetic field, forces act on the particle and the beam deflected from its straight line path. A current flowing through a conductor is like a beam of moving charges and thus can be deflected by a magnetic field.

Working Principle

Hall Effect Sensors consists of a thin piece of rectangular p-type semiconductor material such as GaAs, indium arsenide passing a continuous current through itself. When the device is placed within a magnetic field, the magnetic flux line exerts a force on the semiconductor material which deflects the charges carries, electrons and holes, to either side of the semiconductor slab. As these electron and holes move sideward a potential difference is produced between the two sides of the semiconductor material by the build-up of these charges carries. Then the movement of the electron through the semiconductor materials affected by the presence of an external magnetic field which is at the right angle to it and this effect is greater in a flat rectangular shaped material. The Hall effect provides information regarding the types of magnetic poles and the magnitude of the magnetic field. Hall effect sensors are available with either linear or digital outputs. The output signal for linear sensors is taken directly from the output of the operational amplifiers with the output voltage being directly proportional to the magnetic field passing through the Hall sensors.

Applications

Hall Effects sensor is activated by a magnetic field and in many application, the device can be operated by a single permanent magnet attached to a moving device. There are many different types of magnet movement such as Head on, sideways, push-pull etc sensing movements.

1. The Hall effect sensors are immune to environmental contaminants and can be used under severe service conditions. Such a sensor can be used as position, displacement and proximity sensor if the object being sensed is fitted with a small permanent magnet. Can be used to determine the level of fuel in an automobile fuel tank. A magnet is attached to a float and as the level of fuel changes so that float distance from the Hall sensor changes. The results are a Hall Voltage output which is a measure of the distance of the float from the sensor and hence the level of the fuel in tank determined.
2. Another application of hall effect sensors is in the brushless D.C. Motors. With such motors, it is necessary to determine when the permanent magnet rotor is correctly aligned with the winding on the stators so that the current through the winding can be switched on at the right instant to maintain the rotor rotation.