In electronic ignition systems the contact breaker is eliminated and the primary circuit is switched or triggered electronically.
In induction type systems, the pulse generator has a stator mounted on the distributor body and a rotor unit, called a reluctor, attached to the distributor shaft. The stator has a circular permanent magnet with a number of projections or teeth corresponding to the number of engine cylinders, and a stationary coil of fine enameled copper wire wound on a plastic reel and positioned inside the magnet. The reluctor has the same number of teeth as the stator and, as it rotates, these teeth approach and leave the stator teeth, changing the air gap between them. As this occurs, the strength of the magnetic field changes, increasing as the teeth approach, reaching a maximum when they are in alignment, and decreasing as they move away.
As the stationary winding is influenced by the magnetic field, then, in accordance with Faraday's Law, a voltage is induced across the ends of the winding, each time the magnetic field changes. And if the winding forms part of a complete circuit, the voltage will cause a current to flow.
As the teeth approach, the strength of the magnetic field is increasing. This induces a voltage and current flow in the winding. The polarity of the voltage is said to be positive as it produces a current flow in a certain direction. When the teeth are in alignment, the magnetic field is at its strongest but, at that point, it is not changing. Voltage and current now fall to zero.
As the teeth move away, the strength of the magnetic field changes again, and once again voltage and current flow is induced in the winding. This time, current flow is in the opposite direction, and the polarity is now said to be negative. Since polarity changes every time the teeth approach and leave the stator teeth, the voltage produced is an A.C. voltage, and current flow is an alternating current.
