One of the primary purposes of catoolRT and the feature that distinguishes it from normal data acquisition software is its ability to acquire and store data in the crank angle domain rather than time. Data is referenced either by cycle or the crank angle of a particular cycle.
In order to achieve this not only must the cylinder pressure or other engine signal be recorded, but also an encoder signal that indicates angular position is required. Historically this would have been a rotary encoder with a high number of pulses per rotation and a marker signal once per revolution to determine TDC. Encoders are difficult to package, especially for in-vehicle usage and suffer reliability problems due vibration and physical misalignment between the crankshaft and encoder. catoolRT can use rotary encoders, however, there is an easier way.
Most engines require some form of rotary encoding for the engine control module to work and this sensor can also be used by catoolRT to determine engine position. Usually this consists of either a toothed wheel mounted in or at the end of the crankshaft or machinings on the flywheel. A variable reluctance or hall sensor senses the timing marks, generating an electrical signal indicating angular position. Most production systems use a pattern of missing teeth to determine where the engine is in its rotational cycle.