Innovate Motorsports LogWorks 3 - Manual (Page 12)

LogWorks3_Manual_1.01.doc - 12 -
The engine state is ultimately controlled by the driver’s right foot. The fastest external muscle in
humans is the eye-lid muscle. It goes through one blink-cycle in about 100 milliseconds.
A mathematician named Harry Nyquist found out (in 1928), that for anything that you want to
record, you only need to record at twice the maximum frequency contained in the recorded signal.
So, for the human eye-lid, the required minimum logging speed is 20 times/second. The human
foot, controlling a gas pedal, is much slower. Remember, the frequency is not measured from idle
to WOT, but from idle to WOT and back.
The second parameter determining the logging speed is the statistical nature of the combustion
process itself. No two combustion events in an engine are identical. Therefore, to get meaningful
data, multiple combustion events must be averaged to see the overall effects. If each combustion
event is analyzed and recorded, meaningful tuning data can’t be seen in most cases. At 6000
RPM an engine goes through 50 engine cycles per second (a 4-stroke engine cycle requires two
rotations per cycle). At a logging speed of 12.5 samples per second this would mean that the
resulting data is the average of 4 engine cycles.
The above means that data logging engine data needs to be done at 10-15 samples per second.
Anything more creates only more data points which do not contain any additional information, but
are harder to analyze.
The Innovate Modular Tuning System samples engine data at 12.2 samples/second.
This sample rate is the rate for a sample containing multiple sensor data, each
sampled at the same time instance, NOT the total channel rate.
When evaluating data-logging products be very aware of the difference between channel rate and
sample rate. Many manufacturers specify the channel rate, but claim it as sample rate. For
example if a data logging system records 30 data channels, but reads each in turn only once per
second, the channel rate is 30 per second, but the sample rate is only 1 per second.
This is especially problematic if the channels are not sampled at the same instance in time, but at
whenever it is the turn for this channel to be read. The channel data, when taken and interpreted
as sample, do not correlate anymore, because each reflect the engine state at up to 1 second
apart and there is no way to correlate them. Many OBDII based systems log this way because of
the limited speed of OBDII, but some of the manufacturers claim 30 samples or more per
second.
Higher logging speeds
There are situations when higher logging speeds are needed. To analyze engine data on a crank
degree basis at a resolution of 1 crank degree, requires measuring at 72000 times per second at
6000 RPM ( 6000 * 360 degrees * 2 [Nyquist] / 60 ). The applications for this are very specialized.
An example is to analyze the point (in crank degrees) where flywheel acceleration is fastest. With
the availability of fast and cheap microprocessors today this data can be analyzed on the fly and
then the results logged (for example as max. acceleration point) at a much lower speed of 10-15
samples per second.
Another application for higher logging speeds is suspension analysis. There typically the shock
velocity needs to be known under various conditions. Measuring rates of 1000-2000 times/second
are required to calculate shock velocity and travel amplitude. But again, this data can be
processed on the fly and then get logged at lower speeds by modern microprocessors.