MoTeC Knock OKM - Manual (Page 6)

6 Configuration
Configuration
When suffering detonation, each engine/chassis combination and associated
accessory package resonates at different frequencies. To configure an
electronic knock control system, the exact combination of engine, engine
mount, exhaust system, alternator and starter etc. must have been fitted.
A reliable electronic knock control system requires detecting knock accurately
and differentiating knock from normal engine noise.
MoTeC’s knock modules use the vehicle’s original, factory-fitted knock
sensors to detect detonation, improving this detection by reducing the
influence of background engine noise using a combination of data gating and
frequency filtering.
The engine sound energy during engine operation will vary for different
frequencies in the spectrum. The knock sound energy will be more prominent
at certain frequencies.
A competent tuner needs to carry out a frequency analysis to determine the
frequency where the difference of the engine sound with and without
detonation is most clear to detect. The centre frequency settings of the Knock
Module must match this frequency.
The Knock Control system in the ECU can then be configured to adjust the
ignition according to measured knock levels.
Knock Detection
Knock Sensor
The knock sensor measures the engine vibrations and turns this into an AC
waveform output.
The next figure shows a zoomed in view of typical knock sensor signal
(captured using Gold Wave Audio Analysis Software
www.goldwave.com ).
Audio signal output from a knock sensor