Re: How to get the output from the light dimmer?



>
> Does a light dimmer produce "harmonic distortions to the main supply" ?

It depends on quite what you mean. At the output end, most certainly.
Running at 50%, the triac or SCR pair will turn on when the voltage is
at its peak, with a huge hard edge. The 'clean up' inductors slow this
down a bit, but it's still largely there, and will to some extent
reflect back into the incoming supply, as many an unfortunate sound man
can bear witness.

Old-fashioned thyratrons were even worse (for the young, these are
vacuum tubes which work in the same way, and at high power). They were
installed at Yale, by George Izenour, and by Strand in some theatres
and TV studios.

They provided a simple solution to remote control. Not a cheap one,
though. To start with, the filament heating had to run all the time.
This cost you in power and in ventilation. Then, you needed to run them
on three-phase star supplies, with a DC output. This meant that the
total load current was flowing in the neutral. Supply companies don't
like this, so you had to fit a star-delta transformer capable of
dealing with the whole load. I suppose that it must have been
financially viable, since there were a few installations, but it must
have been a close thing.

> When I`ve checked the output from STM dimmers the sine wave is chopped,
> only part of each cycle is displyed, as you increase the output more of
> the sine wave appears until you get the full wave and full intensity.
> Just connect an oscilloscope accros te output and you willl see the
> waveform.
> Cheers
> Gerry Harris

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