A modern engine’s ECU needs to know what position the engine is in at a given moment in order to calculate correct ignition timing and in the case of sequential fuel injection setups, correct fuel injection timing.

Variable reluctance (VR sensor) trigger sensors are commonly used for automotive engine control applications to accurately determine the position of a crankshaft or camshaft. The system typically consists of a trigger sensor and a toothed wheel that passes across the face of the sensor. As the tooth passes across the face of the sensor, the sensor generates a waveform which can be processed by the engine management system and used to indicate the passing of the tooth on the flywheel or trigger wheel.