MoTeC Knock OKM - Manual (Page 13)

MoTeC Configuration 13
Examples
The following examples show how to interpret the data and choose the centre
frequency.
Example 1
In the next spectrogram, increased energy levels show consistently at
8 kHz. The noise at this frequency is constant even when the engine is not
detonating, therefore we can assume that this is normal engine
background noise. Detonation, introduced via an ignition timing adjustment
in the ECU, can be seen at the 3.5 second mark. Here extra energy levels
are seen throughout all frequencies.
To determine which frequency has the best ratio between little background
noise energy and high detonation intensity compare the areas with and
without detonation.
In the example, at 5 kHz there is little background noise and a touch of
yellow (high energy) at the detonation point. The highest detonation
energy is at 8 kHz, however the background noise is also high here.
To help selecting the best centre frequency, experiment with different
settings while downloading the log files from the ECU. Analyse the log files
using i2 data analysis software.
The log files will show the individual cylinder knock channels. They are
represented as a percentage. The absolute value is at this moment not
relevant.
Important is a low background noise level and a high actual knock
signal.
The log file with a setting of 8 kHz might equal background noise levels of
approximately 60% and mild knock shows peaks of 90%.
A log file with a setting of 5 kHz might equal background noise levels of
approx 25% and mild knock showing peaks of 70%.
Therefore a centre frequency setting of 5 kHz would in this example likely
be the best.
Note:
The centre frequency will affect the overall level of the knock voltage
channel.