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On 18 Sep 2006 at 17:02, Robert Dexter wrote: > I bought a dwell meter at a garage sale. For a 4 cy > engine, it reads around 25 degrees. IT seems that with > a approx 50 degree dwell that looking at it with an > oscilloscope should show a waveform that is half high > and half low. Anyone have experiance using a scope for > dwell measurements? You can certainly do this with a scope, but most of the time that's overkill. 45 degrees would correspond to a 50% duty cycle (45 is half of 90 and each cylinder gets 90 degrees of the distributor rotation.) Your dwell meter is probably made to work with 8 cylinder engines, where a 50% duty cycle means 22.5 degrees of dwell. Most dwell meters have a switch for different numbers of cylinders or different scales to read from depending on your number of cylinders. If you try this with a scope, be aware that there are some rather high voltage spikes that ride on top of the 50/50 signal trace, so be careful not to blow up the input to your scope. A 10x probe should protect you from harm there, but even then, the scope should never be connected to the HV coil terminal. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~