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Re: [TCML] Tesla coil EM Gauss readings



Mddeming@xxxxxxx wrote:
In a message dated 2/24/08 8:50:55 P.M. Eastern Standard Time, jimlux@xxxxxxxxxxxxx writes:


You can also calibrate your probe with a pair of Helmholtz coils.. Two parallel coils separated by their radius (i.e. 10 cm diameter separated by 5 cm). It has an area in the middle that's fairly uniform field, and you can calculate the field by physics, if you know the current. You put an AC current in, stick your probe in, and go to it.




Hi Jim,
This is absolutely correct, but what percentage of newbies (or others) would have any idea what the required physics calculations are? Matt D.


<grin>Why those that take the first hit on Google for Helmholtz coil (which happens to be the wikipedia entry):
http://en.wikipedia.org/wiki/Helmholtz_coil

B= (4/5)^1.5 * mu0 * n * I /R
mu0 is 4piE-7
n is number of turns
I is current
R is radius


B= 8.9918E-7 * n * I / R


by the way, if you want a field comparable to that of Earth (1 Gauss around 1E-4 tesla) with 1m diameter coils, it takes about 1 amp through 56 turns on each coil. If you assume perfect coupling between the coils, that works out to about 32 mH of inductance, which is about like a typical woofer, so bear that in mind when designing your drive circuit.
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