Re: MMC dissipation factor measurement

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Looking in NBS circular 74, I see mention of some very sophisticated
calorimetric techniques.. where you run two different frequencies through
two different capacitors, then interchange them, thereby cancelling out
some of the bias errors. (page 178)
Further pages talk about various substitution approaches, where you put in
known resistances to replace the unknown, thereby removing errors in the
measuring instrument (which will always be measuring exactly the same value).

Then, there is a technique where you hook the unknown capacitor in series
with an inductor. You hit the circuit with an impulse and measure the
decrement. Then, you add a known resistor in series, and measure the
decrement again.  

Yet another approach is to use a damped sinusoid as the excitation (now
where would you get that!) (because of the difficulty of getting a pure
impulse).. Again, you add a known resistor in series.

And, there's a technique where you measure the Q of a tuned circuit with a
swept sine wave...


Tesla list wrote:
> 
> Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
> 
> Hi Terry,
> 
> On 16 May 2002, at 21:13, Tesla list wrote:
> 
> > Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> >
> > Hi All,
> >
> > The question comes to me tonight....
> >
> > I have a TEK 3012 scope.  I have a TEK 5100 voltage probe, lots of Pearson
> > current monitor CTs...  I have a lot of sine wave generators with low
> > impedance...  Like 350kHZ at 5 amps...
> >
> > So, would I have any chance "in the hot place" of measuring the dissipation
> > factor of a poly MMC cap?  Like <0.001 dissipation factor...
> >
> > I guess I would have to detect the difference between 90 degrees and
> > 89.87856 degrees to find the dissipation factor...
> >
> > Sounds doable but maybe someone out there has "been there, done that..."  I
> > was just asked the question and "I" have not thought much on it cause I am
> > sleepy :o)  Might need a step down transformer to get a really low source
> Z....
> >
> > Cheers,
> >
> >       Terry
> 
> You may be able to do it on an incremental basis using bridge
> techniques. I am suggesting measuring the difference between two
> different types of capacitor, the one with the lowest esr score then
> going on to be the standard for a succeeding test which compares
> another. Hazy I know.
> 
> Regards,
> Malcolm