Crankshaft Angle Sensor
The signal rotor plate in the distributor, rotates with the distributor shaft. It has 360 slits at 1° intervals around its outer circumference. These provide the 1° signal necessary to control engine RPM and ignition timing. The signal rotor plate also has an additional 6 slits (nearer center of ring) at 60° intervals to detect crank angle - the position of each piston.
The crankshaft angle sensor, which is built into the distributor, has 2 diodes and a wave-forming circuit. See Fig 1. When the signal rotor plate passes the space between the light emitting diode (LED) and photo diode, the slit to the signal rotor plate alternately cuts through the light which is sent to the photo diode from the LED.
This causes an alternative voltage, which is converted into an on-off pulse by the wave-forming circuit and sent to the control unit.
Crankshaft angle sensor is built into distributor.