Re: Alternating Current

[brian whatcott <inet@INTELLISYS.NET>]

At 16:43 1/29/99 -0500, David wrote:
> I just did a lab today with my Pre Calculus class. Since we have
> introduced sinusoidal variation I had them use a CBL to look at the
> light intensity from an incandescent bulb sampling every .0001 seconds
> for 100 data points..... The frequency came out consistently at
> 124Hz by the way and I wonder if the power company is typically this far
> off their standard value of 2*60Hz?...
>        David Abineri     dabineri@choice.net

I would be more comfortable treating David's results as an
investigation of the systematic errors of a data acquisition
setup.    Oops! How non-U;
I meant the deterministic experimental ..ar..discrepancies.
(;-))

 I expect that David's dac software ignores the convert time
(as trivial in many cases) and so I can propose that the 100
 samples at nominal 100 microsecond intervals, may well have
 comprised a 100 microsecond interval followed by a 3 or 4
microsecond convert/transfer delay.

 With this hypothesis, one could rerun the data in order to
refine the conversion/transfer interval by taking samples at
longer intervals: the limiting interval is defined by Nyquist,
so we set the longest interval shorter than 1/240 second say
4 milliseconds: A series at 250 microseconds, 1 millisecond and
 4 millisecond intervals (using whichever intervals are practical)
should show an approach to 120Hz in the limit.

Brian
brian whatcott <inet@intellisys.net>
Altus OK