Missing teeth

Dave Johnson dajohnson at dek.com
Thu Jun 27 08:04:15 GMT 1996


Is there anyone out there that can answer a question for me?

A lot of ECUs sense engine speed by measuring the time between pulses from a 
toothed wheel on the crankshaft, fair enough, I understand that. But, to get 
engine position they use a missing tooth to provide a datum mark.

What I want to know is how exactly do thay know when they are at that datum 
mark? For instance, when first starting the engine do they compare the time 
between pulses and when they get a much larger time compared to previous 
ones they think oh I'm at the datum! I just can't quite get my head around 
it at the moment.

It's probably quite staight forward and logical but I can't see it.

Thanks in advance,

Dave Johnson

email:- dajohnson at dek.com


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