ORIGINAL: FenceMagnet
"The hall switch generates a square wave. When the magnet approches it arms, goes high. It triggers when the magnet leaves, goes low. The duration of the square wave is the dwell time.."
agreed, but the magnetic field shape is not a square wave, so the distance from the magnet to the sensor will, at some point, begin to affect the width of the pulse....
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Agreed there many variables the, air gap, strength of the magnet, size of the magnet, and some small differences in the sensors. The average cranking speed on a 70cc engine is in the 500rpm range. The 180 rpm gives enough room for the variables.