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One of the constraints is that its resistance should be around 8R and be capable of dissipating 50W. It will be driven at audio frequencies, so its impedance will always be greater than 8R, just in case anyone shorts the amp into it with DC (although around 20Hz is the min I expect). Typically though, it will handle low duty cycle pulses of 2mS and 10mS.
-- Dirk http://www.transcendence.me.uk/ - Transcendence UK http://www.theconsensus.org/ - A UK political party http://www.blogtalkradio.com/onetribe - Occult Talk Show
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OK, 80m of wire with 30 cm of diameter, pi*D is about 1m so 80 turns of wire. Sounds a lot like the some coils we use for optical pumping. Two of them in a Helmholtz configuration. 12" diameter with
120 turns per side. Resistance about 10 ohms, and they can dissipate 100 watts forever, (Given a room temperature environment.)As Wim said the field at large distances... say more than 10 feet (3m) goes as the diameter. With a 10 cm diameter there will be less area to get rid of the heat, but if you pick the right coil form it could still be OK. (We wrap the coils on phenolic, which is not the best heat conductor.)
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OK, I looked up the specs for the optical pumping coils at work today. There are 154 turns per side, total resistance of pair is 10 ohms. The inductance of the pair is about 33 mH. Your coil with only
80 turns, might have an inducatnce of 2 to 3 mH. With 10 ohms that will give you a time constant of 0.3ms (or so). Now at what frequency did you to run this?George h.
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Between 100Hz and 2kHz, single cycle sine wave pulses, non-resonant. What do your optical pumping coils do? BTW, thanks for the help.
-- Dirk http://www.transcendence.me.uk/ - Transcendence UK http://www.theconsensus.org/ - A UK political party http://www.blogtalkradio.com/onetribe - Occult Talk Show
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Hello Dirk, The 100Hz looks OK but you'll have to check the L/R time constant to see how it will work at 2kHz.
"> What do your optical pumping coils do?"
Provide a magnetic field.... up to 20+ Gauss, homogeneous to better than one part in 10^4 over the 25mm sample size. (The 'good' ones are better than one part in 10^5.) Here's a picture of them attached to the rest of the apparatus.
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Alas that is the B field inside the coil. The question was about the field way outside the coil at point X, where X >> D.
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