LUCAS "Opus" Electronic Ignition System: Operation
With the ignition switch turned "OFF" and the engine stopped, the distributor reluctor or timing rotor is normally positioned so the teeth or iron rods do not align with the iron core of the pick-up coil. When the ignition switch is turned "ON", a power transistor in the electronic control module (amplifier) completes the ignition coil primary winding circuit.
At the same time a pulsating alternating current voltage is applied by the module to the distributor pick-up coil windings. A small alternating current voltage is produced, and pick-up coil windings are magnetically balanced.
The voltage at the pick-up coil is applied to the amplifier unit, but is insufficient to affect the transistor controlling the ignition coil primary circuit.
As the engine is cranked, the teeth or the iron rods come in alignment with the iron core of the pick-up coil. This causes a magnetic unbalancing and voltage increases to maximum as each tooth or rod passes the pick-up coil. The higher voltage signal is then transmitted to the control module. The transistor is switched off and the coil primary windings' magnetic field collapses.
This results in a high voltage surge in the secondary, which is transmitted to each spark plug by the distributor rotor.