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Re: E-Tesla = Medhurst
At 04:49 PM 6/12/00 -0400, you wrote:
>I thought i would try to get a few points from your programe for the ends of
>Medhursts's table. But the programe you gave the link to does not work on
>my PC. After inputting the data it asks if the data is correct if I reply
>yes or no it contiuously ouputs an error message???
The "C" version needs a "1" or "0". I had trouble with the alphanumeric
input stuff and had to "punt" 0:-) If you input a letter it goes nuts.
Simply input the number "1".
The BASIC version is "y" or "n".
>In the file I sent you will note, if you have not already done so,
>that there is a minimum in med C.
>I was trying to check if E-tesla reproduced that minimum. I don't
>understand why If med C is just referred intrinsic C linear wieghted. Why
>would the intrinsic C go down then up as you increase the hieght? I find it
>hard to accept that when you increase one dimension of something its C goes
>down?? If this is true then reffering process is more complicated than I
Medhurst bends around and starts to go back up at low H/D ratios but I
didn't run E-Tesla down there. I will do so...
>From: Tesla List <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
>Cc: alwynj48-at-earthlink-dot-net <alwynj48-at-earthlink-dot-net>; malcolm.watts-at-wnp.ac.nz
>Date: Monday, June 12, 2000 2:10 AM
>Subject: Re: E-Tesla = Medhurst
>>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>>At 01:40 PM 6/11/00 -0400, you wrote:
>>>After a little more thought or was it a lot more thought.
>>>For a large parallel C the voltage a long the coil approaches a linear
>>>function regardless of what the distribution is with out parallel C. ie
>>>current flowing in the distibuted intrinsic C hardly effects the voltage
>>>across the coil because the coil current is much higher than the intrinsic
>>>Hence the additional current flowing in to the distributed intrinsic C is
>>>only a function of the voltage and C. This is even true for low H/D
>>>with almost unity coupling (auto transformer action).
>>>Under such condition the distibuted intrinsic C can be refereed to one end
>>>by simple summing the currents. Because the currents are proportional to
>>>the voltage a voltage weighted intrinsic C is equal to a single C you must
>>>put in parallel with the coil to have the same total current flow that the
>>>distibuted intrinsic C had.
>>>Hence if you run E-Tesla with a linear voltage and on an isolated coil it
>>>will produce med C. This is a theoretically valid comparison and should
>>>correlate to approximately. 1% in C not F. A good test of the theory and
>>Ok. I stripped out E-Tesla5.50 to put a linear voltage on the secondary
>>and stick it in free space and all that. The program is at:
>>I then ran the program with a 200 grid on 10 inch diameter coil of various
>>lengths. I then compared the results to Medhurst.
>>H/D Cmed C ET5 calc Error %
>>10.0 1.32 1.2056 -8.66
>>9.0 1.22 1.1238 -7.89
>>8.0 1.12 1.0482 -6.41
>>7.0 1.01 0.96745 -4.21
>>6.0 0.92 0.88716 -3.57
>>5.0 0.81 0.80313 -0.85
>>4.5 0.77 0.75848 -1.50
>>4.0 0.72 0.71428 -0.79
>>3.5 0.67 0.66897 -0.15
>>3.0 0.61 0.62244 2.04
>>2.5 0.56 0.57424 2.54
>>2.0 0.5 0.52573 5.15
>>1.5 0.47 0.4758 1.23
>>1.0 0.46 0.42783 -6.99
>>The graph is at:
>>Note that both graphs have a bend at 5.0!?! Must be something magical
>>happening at that point. Below 5.0 Medhurst tracks very well until the
>>coils get really small. I wonder if the error is him or us? :-) ET5 looks
>>like two straight lines while the Medhurst graph is showing obvious signs
>>of a little experimental error. The program did about 300 billion more
>>calculations than Medhurst did so it should be straight! :-)) I wonder if
>>I dare say that the computed numbers "may" be more accurate than Medhurst's
>>in the 2.5 to 5.0 range?
>>Looks like Bob is again right!!
>>>If you run it with a ground plain it will produce med C with a ground
>>>But as Medhurst did not produce such a table you can not make any valid
>>>comparison. The true C / TM equation is again theoretically valid for an
>>>When I say valid for..... I dont mean its not valid for other conditions
>>>means only that I can only prove its valid for that condition/s.
>>>So E-Tesla can be said to be theoretically accurate for coils with
>>>approximately 1000 turns (low turn to turn C effects), for large top loads
>>>and with a ground plain sufficiently below the coil (at least several
>>>diameters) that the inductance is valid.
>>>Note E-Tesla must include some internal C (turn to turn C) effects
>>>the C is determined with a voltage profile as opposed to a unity profile
>>>(the correct way to calculate intrinsic C) then weighting the result with
>>>the voltage profile. However as the internal C has mostly internal
>>>current I don't know if it can be refereed to the one end and I don't if
>>>you treat the internal coupled flux is valid or correctly produces a
>>>reffered C to one end. That will require more thought but as I believe
>>>a small effect I am not motivated to try. If you try it both ways and the
>>>answer (refereed C or med C) is significantly different then I will be
>>>motivated to try.
>>>Now what about the self resonant case. When the only current flowing in
>>>coil is due to the distributed intrinsic C both the voltage and current
>>>not linear so the above method of referring the intrinsic C to one end is
>>>not valid. A 5% to 10% error in F is 10% to 20% error in C or L.
>>I am working on such things to further increase accuracy...
>>>You can put this on the list if you think anybody else is interested