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Re: Frequency vs temperature
Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
Is there a data file (having not looked this morning at your raw data) that
has just F,R, and T as a function of time? (i.e. not the raw scope traces)
Do you have a ballpark estimate for the mass of the top load (to estimate
thermal inertia) and likewise for the secondary.. (Or, I can estimate from
the size of the PVC+ mass of windings?)
Then, I can see if there is a suitable correlation between variations in F
and temperature of various components (I expect the top load to have a
shorter time constant than the secondary...it's aluminum and has a much
larger surface area to mass ratio, so it will track air temperature).
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
Sent: Thursday, May 02, 2002 7:16 PM
Subject: Re: Frequency vs temperature
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> Hi Jim,
> At 05:37 PM 5/2/2002 -0700, you wrote:
> >Looking over your extensive F, R, and Q data...
> >How much would you expect the Fres to change over temperature... You're
> >looking at tiny fractions of a % for frequency, and it seems to me that
> >dimensional changes in your coil and topload will be on that order...
> A great thought! Normally we would not be able to see frequency variation
> due to thermal expansion but this things is really sensitive. The data is
> 10,000 points long, 9 bits deep and the signal is averaged over 64 shots
> there is a lot of noise reduction. The raw files are at:
> The even files are the scope captures and the odd data is the temperature
> probe signal. A laptop computer picks the data off the scope and stores
> on the hot-streamer computer. The Sun workstation grabs it and crunches
> the data and stores back the nice HTML data file. Paul's programs do all
> the work :-))
> >Resistance changes over temperature are going to be significant too.. and
> >that slightly changes the apparent resonant frequency (i.e. it's really
> >=sqrt(1/LC) but a function of LC and R.. although.. your Q of 200 is high
> >enough that this effect might be small...
> >A quick and dirty Wheeler calculation, while not accurate in absolute
> >to hundredths of a percent, could probably give you a sensitivity... that
> >is, L goes as some function (x/(x+1)?) of Length.... and so
> >forth...obviously N isn't changing...but length and diameter certainly
> It is a white PVC tube wound with #24 copper wire. There is no coating.
> >Likewise, C of topload will also change as a function of temperature (CTE
> >aluminum is what? 23 ppm/degree... so a 30C change will be a dimensional
> >change of about 700 ppm, and, to a first order, capacitance will change
> >same (that is, about 0.07%), resulting in a 0.03% frequency change,
> >is of the same magnitude as you are seeing...
> >The elliptical F vs T curves seem to indicate a thermal/mechanical time
> >between parts of the system, that is, some things get bigger and smaller
> >different rates than other things...
> >This is pretty nifty, in that you can actually make reasonably precise
> >measurements (assuming that the error bars are reasonably sized!)
> Paul has that stuff figured out so I will defer to him about error margin.
> I try not to breath or go near it since it is sensitive to disturbances
> from the experimenter ;-)
> When rain collects on the roof of the garage, Q1 is obviously affected.
> Apparently, loss in the wet roof sucks energy from the coil. It is
> interesting that q3 and q5 seem to be affected by the deeper dampness in
> the woodwork or something. Here are some pictures but they are a little
> dated. I am afraid to go near it to take new ones ;)