Hall Effect Sensor: Description and Operation

Hall-Effect Sensor Construction:

PURPOSE
The hall-effect sensor supplies the ignition amplifier with information regarding crankshaft position.

LOCATION
Located in the distributor.

CONSTRUCTION
The hall-effect sensor (1) is a U-shaped element with an opening for the trigger rotor (2). The number of trigger vanes is equal to the number of cylinders in the engine.

The sensor consists of a hall-IC element (3) incorporating a hall-effect detector and a transistor amplifier. A magnet (4) with a three-pole connector (5) is located on the opposite side of the rotor to the hall-IC element. The connector terminals are connected to a 12V supply (+) from the control unit, a 5V reference signal (generated by the hall-IC element) and a ground (-) connection.

Hall-Effect Sensor Operation:

OPERATION
In position (A), the magnetic field is blocked by the trigger rotor vane and the hall-effect is absent. The hall-IC element registers a low or no voltage, sending its 5V reference signal (O) to the ECU. The ignition ECU now senses no voltage drop and knows the trigger rotor is in its "closed" position.

In position (B), the magnetic field is opened by the opening in the trigger rotor and the hall-effect is generated. The hall-IC element registers the voltage generated by the magnetic field, grounding the 5V reference signal (O) circuit. The ignition ECU now senses a voltage drop to 0V and knows the trigger rotor is in its "open" position.

The signal from the hall-effect sensor varies therefore between 0 and 5 volts in the form of a square-wave (digital) signal.

Hall-Effect Sensor Signal:

SIGNAL
A1) Signal increases from 0 to 5V. Ignition ECU starts to calculate the timing for next ignition pulse.
A2) Signal falls from 5 - 0V. Ignition ECU starts countdown and delivers ignition pulse as computed to the power stage.
B) Positive flank. Hall-IC element is unaffected by the magnetic field.
C) Negative flank. Hall-IC elment is influenced by the magnetic field.