Re: [TCML] Re: Dummy load for optimum cap size Experimentation

[David Sharpe <sparktron01@xxxxxxxxx>]

Gary

Might want to borrow an industry standard DVM (like
a Fluke 87) and compare the readings in your experiment.
That being said, I agree the analog meter is more "average"
responding then the RMS capabilities of modern DVM, and
that is most probably where the descrepancy is.

But that is why I'm suggesting using a Fluke, their measurement
accuracy (at least for hand held models) is well documented
and usually significantly less then 1% error, even measuring
high THD signals, such as Variable Frequency Drives output
voltages.

Regards


On Sun, Oct 3, 2010 at 3:11 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:
> I'm making slow but steady progress in my experiment to determine the best
> cap size based on using a halogen lamp dummy in place of a primary, and
> monotoring the light intensity to indicate how much power is being
> processed.
>
> I'm recording the power at 120V and at full Variac setting.  The full Variac
> setting is typically ~135V under load.  It changes slightly depending on the
> cap value, but it is what it is.  When I set the Variac to get 120V, I
> monitored the voltage with both a Wavetec 27XT DMM, and an old lab-quality
> Weston analog meter, calibrated at the 120V point with the 27XT, with 120V
> from the Variac, under no load.
>
> But when the Variac is under load from the NST, there can be a significant
> difference between the two meters (113V vs. 120V).  I'm speculating that
> this is due to the loaded Variac output waveform being distorted, and the
> two meters see this differently.
>
> I don't own a true-RMS meter, so I have to decide which of these two
> readings to believe.  I have been using the analog meter.  Can anyone
> suggest which one might be closer to a true-RMS value?
>
> Thanks, Gary Lau
> MA, USA
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-- 
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA

Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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