Hall effect sensor work is a type of magnetic sensor. A Hall effect sensor is a transducer that varies its output voltage in response to changes in magnetic field. In 1879 Edwin Hall discovered that: ‘when a conductor or semiconductor with current flowing in one direction was introduced perpendicular to a magnetic field a voltage could be measured at right angles to the current path’. The voltage is directly proportional to the number of flux lines passing through the conductor, the angle at which they pass through it, and the amount of current used.
When a current-carrying conductor is placed into a magnetic field, a voltage will be generated perpendicular to both the current and the field. This principle is known as the Hall effect.
Figure illustrates the basic principle of the Hall effect. It shows a thin sheet of semiconducting material (Hall element) through which a current is passed. The output connections are perpendicular to the direction of current. When no magnetic field is present as (a0, current distribution is uniform and no potential difference is seen across the output.
When a perpendicular magnetic field is present, (b), a force is exerted on the current. This force disturbs the current distribution, resulting in a potential difference (voltage) across the output. This voltage is the Hall voltage (VH).
The Hall voltage is proportional to the vector cross product of the current (l) and the magnetic flux density (B).
VHα IB
VH = KH
Where KH is the Hall coefficient
t is the thickness of the Hall elements.
The Hall element is the basic magnetic field sensor. It requires signal conditioning to make the output usable for most applications. The signal conditioning electronics needed are amplifier stage and temperature compensation.
Voltage regulation is needed when operating from an unregulated supply. Image illustrates a basic Hall effect sensor.
The Hall effect sensor can also be used to measure fuel level in a fuel tank. The float has buoyancy in the fuel. It floats up as the fuel becomes more. The gap between the magnet and hall sensor will changed. It results in the changing of the output. The springs allow the float to move only vertically.
Applications
- Hall sensor are used for proximity switching, positioning, speed detection, and current sensing application.
- Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing or tachometers.
- They are used in brushless DC electric motors to detect the position of the permanent magnet.
- Typical applications are the detection of a moving part, replacing a mechanical limit switch. Another common use is in indexing of rotational or translational motion.
Advantages
- Relative low cost compared to electromagnetic switches
- High frequency operation is possible.
- Multiple purpose usage as displacement, position and proximity sensors.
- Solid and robust, capable of working in a severe environmental conditions as they are immune to humidity contamination
- No contact bounce problem.
Disadvantages
Sensor becomes weak during offset effects caused by misalignment of contact in Hall element and piezo-resistive effects.
