Hall Effect Sensor: Description and Operation

Hall Sender Location:

The Hall sender or "generator", which is located within the ignition distributor, creates a square wave signal which is used by the ignition (Hall) control unit as a reference for ignition timing.

Hall Generator:

The Hall system simply produces an "ON", "OFF", signal for ignition control. It consists of a semiconductor wafer element and a permanent magnet. A rotating shutter, called the shutter wheel, acts as a switching device to produce the Hall signal.

The Hall Effect:

BASIC OPERATION
Current is applied to the semiconductor wafer. When the open section of the shutter wheel is in place, the semiconductor produces a measureable voltage. Based on the presence of this voltage signal, the control unit switches the coil primary current "OFF", this signal is then used by the control unit to discharge the coil. As the shutter wheel rotates through the magnetic field, interrupting the Hall voltage, an off input to the control unit is produced. This voltage off signal to the control unit switches the coil primary current "ON" beginning the coil saturation period (dwell). Maximum dwell is determined by the area of the shutter wheel.


HALL SIGNAL OPERATION IN DETAIL
The Hall sender contains a semiconductor wafer element, and a permanent magnet. When the current flowing through the sender element in the direction of one axis (call it the X axis) is subjected to a magnetic field whose lines of flux cross perpendicular to the direction of current flow (call it the Z axis), electrons (charge carriers) in the current flow are deflected along an axis (call it the Y axis) perpendicular to the "X-Z" plane defined by the direction of current and lines of flux. The resulting difference in the concentration of electrons along opposite edges of the element (perpendicular to the previously defined plane) creates a voltage potential (Hall voltage) which can be measured.

When the distributor is turning, vanes of a metal rotor, called a shutter wheel, alternately pass and block the lines of flux from the permanent magnet. When a vane passes between the magnet and sender, the lines of flux permeate the metal vane and do not reach the sender element. The flux density through the sender element is negligible and the Hall voltage is too small to measure (effectively zero). When no vanes are present between the magnet and sender, the lines of flux pass through the Hall sender creating the Hall effect. The signal generated by the Hall sender is used by the ignition (Hall) control unit to switch the coil primary current "ON" or "OFF".