Hall-Effect Sensors
Hall Effect Sensors
Hall Effect Sensors produce a modulated square wave.
Hall Effect Sensors are electronic switches that react to magnetic fields to rapidly control the flow of current or voltage ON and OFF.
The Hall Sensor consists of an epoxy filled non-magnetic housing containing a hall element and a magnet, and a trigger wheel.
The Hall element is a thin non-magnetic plate which is electrically conductive. (Voltage will flow through the plate.) Electron flow is equal on both sides of the plate.
Since everything between the magnet and the hall element is non-magnetic the magnet (magnetic field) has no effect on the current flow.
As a metal disk or solid area of a toothed wheel, flywheel or other trigger device approaches the sensor, a magnetic field is created between the magnet and the disk.
The magnetic field cause the electron flow to stop on one side of the plate. Electrons continue to flow on the the other side of the plate.
The Hall Sensor Signal is a measurement of the voltage drop between the two sides of the plate or element.
When the magnetic field increases (disc or solid toothed area in front of sensor) the voltage drop across the two sides of the element increases. High voltage on one side, little on the other. The signal output from the sensor is High.
As the disc moves away from the sensor the magnetic fields weakens and is lost. The loss of the magnetic field (blank toothed or open area of the wheel in front of the sensor) produces very little voltage drop across the two sides of the element. The output signal is Low.
This rapid switching of the voltage ON/OFF produces a HIGH/LOW signal that the control module uses to recognize speed and position.
Examples of Hall Effect Sensors
Motor Position Hall Sensors
Hall sensors are used on many electric motors to monitor speed and position. (i.e. electric window motors and sunroof motors.)
The Hall Effect principal is the same except the magnet is placed on the shaft of the motor.
The magnet is aligned to rotate in a precise position in front of the element. The polarization of the magnetic ring causes a polarity switch in the Hall element to occur as it rotates.
The square wave produced provides speed and position information to the control module.
Wheel Speed Hall Effect Sensors
Hall Effect sensors are used to indicate wheel speed.
Conventional Hall Effect Sensors use three wires, power supply (usually 5v or 12v) a ground wire and a signal wire back to the control module.
The Hall Effect sensors used as wheel speed sensors are unique in that they are two wire Hall Effect Sensors.
The two wire sensors eliminate the separate ground wire and the signal wire functions as the ground also.
The unique two wire arrangement provides the control module with a HIGH/LOW signal having a low voltage of .75 volts and a high voltage of 2.5 volts.
Typical Application of Hall Effect sensors
- Crankshaft Sensors
- Camshaft Sensors
- Wheel Speed Sensors
- Motor Position and Speed Sensors (e.g. Window Motor, Sunroof Motor)