RPM Monitoring

[Moofaloof at aol.com]

Hi Brian,
Your 4 position optical crank speed sensor is on the coarse side compared to today's systems in general but there is a wide variation. As an example that parallels your system, GM's LT1 engine has both coarse and fine optical measurements.  The coarse wheel has 4 slots, the fine one has 360.  Optical systems like this are rare with the majority of systems using VR or hall effect sensors working off a ferrous target.  Most OEM systems fall somewhere within the above range in terms of resolution.
jc

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I am a new member, and like you all must be, an automobile enthusiast. I am 
currently going to school for Computer Science/Embedded Systems and did a 
mock up Air/Fuel ratio monitor for a project a little while ago. The 
project also included an RPM monitor which is what I would like to ask 
about. I know that several systems monitor RPMs as a parameter for 
adjustments, and I was wondering what the typical method used is. In my 
mock up system, I actually simulated things using an electric motor, but I 
was spinning it from about 5-10K RPMs. I machined a flywheel with 4 slots 
at the 90 degree points to pass through an optical device and allow me to 
measure the RPMs. I noticed that with the motor spinning that fast with 4 
tics per revolution, I didn't get that great of resolution for the RPM 
data. In an automotive application that typically hangs out in a lower RPM 
range, are the RPMs taken from some kind of higher resolution crankshaft 
position sensor or is the data acquired from the ignition system sufficient 
to base adjustments on?


Best Regards,


Brian St. Jacques

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