13.1.4 Hall effect sensor

Definition and Principle of Hall Effect:

• The Hall effect occurs when a current-carrying semiconductor is placed in a magnetic field. This interaction creates a potential difference that is perpendicular to the direction of the current flow. This voltage is referred to as the Hall voltage $( V_H )$.

• The Hall voltage is proportional to the magnetic flux density of the applied magnetic field. This effect allows Hall sensors to measure magnetic fields by detecting the potential difference created in the semiconductor.

Applications of Hall Effect Sensors:

1. Magnetic Flux Density Measurement:

• Hall sensors are used to measure the magnetic flux density in a field by detecting the potential difference (Hall voltage) generated.

2. Orientation and Angle Monitoring:

• By attaching a magnet to an object, the orientation or angle change of the object can be tracked through the Hall voltage.
• As the object rotates, the component of magnetic flux density detected by the Hall sensor changes. This causes a variation in the Hall voltage, enabling the tracking of the object's angular position.

3. Position Detection:

• The horizontal and vertical position of a magnet relative to the sensor can be determined by moving the magnet across the sensor's face.
• The Hall voltage will vary based on the number of magnetic field lines intersecting the sensor, making it possible to pinpoint the magnet's position.

Tachometers Using Hall Effect Sensors:

• A tachometer is a device that measures the speed of rotation of an engine or other rotating component using a Hall effect sensor. It can be set up in two main ways:
  1. Attaching a Magnet to the Rotating Component:
  • As the magnet passes by a stationary Hall sensor, it creates a pulse of Hall voltage each time it rotates past the sensor.
  2. Using a Toothed Wheel and Stationary Magnet:
  • A magnet is fixed near a toothed wheel attached to the rotating component. The wheel's movement affects the magnetic field strength, resulting in variations in Hall voltage.
• In both setups, the Hall sensor generates a pulsed signal. The frequency of this signal can be used to determine the component's rotational speed.

Advantages of Using Hall Effect Tachometers:

1. High-Speed Measurement: Capable of measuring very high rotation speeds (e.g., over $100$ kHz).
2. Non-Contact Mechanism: As there is no direct contact with the rotating component, no additional frictional forces are introduced.
3. Compact Size: Hall effect sensors are small, allowing for use in confined spaces.