Carl's right.  Assuming both are AC, once you get close in frequency, the
bulb will show the phase difference between the windmill and the power
line.  When it's out, you're in phase.

On Thu, Jan 19, 2012 at 5:13 PM, Harold Hallikainen
<harold@hallikainen.org>wrote:

>
> > I thought it would be interesting to have a windmill with an RPM
> > detector on it.
> >
> > As I understand it, something as simple as an incandescent light bulb
> > across the switch. When there is no light, close the switch. :)
>
>
> But the light would light whether the windmill is going faster or slower
> than the synchronous speed... So, I think an independent RPM measurement
> is required.
>
> Harold
>
--=20
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