When to take timing measurements

[Mike Blakey]

I too measure the period between the +ve edges of two adjacent teeth (6deg). This 
is done for the entire rpm range with a 16bit counter. However, I can choose which 
teeth and when I take the measurement as everything is synchronised to the prime 
mover. From storing max. values from the counter, I get different readings 
depending on which teeth I pick!






brd at paradise.net.nz on 14/03/2001 09:35:08
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Subject:	Re: When to take timing measurements

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>When is best to take a timing measurement ?
>
>I'm using a 60-2 wheel, so can time any 6deg pulse to obtain the engine
RPM.
>Obviously the nearer to TDC the better, but is the max acceleration (on a
4cyl) not
>at 90deg BTDC ? and so would be a better place to take the measurement ?
>


What exactly do you mean by "take a measurement"?.

The approach I use, is that below a certain RPM I measure the period between
teeth
and invert the get the RPM.

Above a certain the RPM, I revert to counting teeth in a period (i.e.
frequency counting).
The period is not synchronised to the engine cycle at all.

The reconstructed "missing" teeth are counted in both schemes (which use the
period of
the last 8 teeth to determine where the next one should be).

The RPM from both methods is passed through a variable length moving
average filter, before being passed to the map lookups...



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