Crank Position via Hall Effect

John S Gwynne jsg
Thu May 12 01:59:09 GMT 1994


   In message <199405120033.RAA02659 at> , you write:
| Placement on the flywheel allows for MUCH more accurate timing, the velocity
| with which the magnet would pass the pickup will narrow the signal pulse by
| around 350% in my particular case, 7" HB vs 24" flywheel.

I don't fully agree... While I agree the angular velocity is greater, what
really count is the "turn on" time. Presumably, we would be doing rising or
falling edge detection with a high speed comparator with hysteresis. The
threshold voltage would be picked as the voltage with the highest derivative
(point on the curve with the fastest rise). This would result in the most
stable triggering point. As such the actual dwell time of the sensor in the
presence of the magnet field is unimportant. What count is the turn on/off
times which are really set, at the speeds we are dealing with, by the device
and the gain in the system.  This necessitates the selection of a good high
speed transducer and comparator. Don't miss understand me, I like the idea;
but the "much more accurate" statement maybe should be "a little more

                                       John S Gwynne
                                          Gwynne.1 at
               T h e   O h i o - S t a t e   U n i v e r s i t y
    ElectroScience Laboratory, 1320 Kinnear Road, Columbus, Ohio 43212, USA
                Telephone: (614) 292-7981 * Fax: (614) 292-7292

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