In Reply to: Re: Measurement of damping factor posted by Steve Eddy on April 14, 2003 at 13:15:15:
Built a superconducting magnet prototype..Dipole field, destined for use in a 4 Tesla MRI solenoidal field. Requirements for the magnet are operation at about 50-75 hz, up to about 500 amps, and needs about 200-300 volts excitation. Course, it's in liquid helium..Coupla problems...
First, the power supply has to deliver those kinda numbers. Second, the magnet is a pure inductance...No resistance, very little capacitance, and huge quantities of energy storage (well, pittance actually, in the kilojoules as opposed to a coupla megajoules, but that's a matter of viewpoint).
We're setting up to test this baby soon at up to 50 hz, but since it's a pure inductance, this baby is gonna push the amp into quadrants 2 and 4. The closest to 1 and 3 will be steady state operation, something we don't worry about, as we've already tested that capability using a 10 kiloamp supply.
But in quadrants 2 and 4, the opposing pass elements are pulling the stored energy into the opposite polarity cap banks (dissipating in the pass elements big time), and sometimes little detail is put into the design for use in those quadrants.
We have to make sure the control of the signal amplitude doesn't go the hell in a handbasket in those quadrants, as part of the test regime will be to have the amp provide a DC level of about 250 amps, and superimpose another 200-250 amps 50 hz, forcing the amp to sink and source big time. Damping factor, as you point out, is a dimensionless number, but it gives an indication of control.
And I wanted to know if any of the amp guys here had any novel techniques for testing these quadrants, and the amp's ability to retain control while being jostled with woofer back emf.
The second problem??
The leads from liquid helium to liquid nitrogen are high temp superconductor. From LN2 to room temp, we use a copper feedthrough, about 1 inch in diameter..1 inch and 500 amps..50 hz? Should be easy, but guess what?
Skin effect rears it's ugly head...Because copper conductivity rises about three orders of magnitude when you go cryogenic. Now, can the copper sheet the current actually goes through really support the current??
And youse guys wuz tinkin skin was only fors audio stuffs?
The magnet:
http://www.bnl.gov/magnets/BioMed/BioMed.aspI got it all over you guys....Because I have the coolest and biggest toys to play with...And he who dies with the most toys wins...
Cheers, John
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Follow Ups
- Hi Steve - John Escallier 04/15/0306:33:36 04/15/03 (63)
- Re: Hi Steve - Steve Eddy 11:14:03 04/15/03 (62)
- Re: Hi Steve - John Escallier 11:36:55 04/15/03 (61)
- Re: Hi Steve - Steve Eddy 12:27:15 04/15/03 (60)
- Re: Hi Steve - John Escallier 12:32:27 04/15/03 (59)
- Re: Hi Steve - Steve Eddy 13:23:47 04/15/03 (58)
- Re: Hi Steve - John Escallier 13:40:21 04/15/03 (57)
- Re: Hi Steve - Steve Eddy 14:28:07 04/15/03 (56)
- Re: Hi Steve - John Escallier 15:43:50 04/15/03 (55)
- Re: Hi Steve - Steve Eddy 18:53:40 04/15/03 (54)
- Re: Hi Steve - John Escallier 22:00:47 04/15/03 (53)
- Re: Hi Steve - Jitter_by_Coffee 06:21:53 04/16/03 (52)
- Will do - jneutron 07:14:53 04/21/03 (0)
- Answers are good. Got some? - jj 12:11:07 04/19/03 (50)
- Hi jj - jneutron 06:35:05 04/21/03 (6)
- Oh, the question was for Jitter.... - jj 00:40:14 04/22/03 (5)
- Re: Oh, the question was for Jitter.... - Jitter_by_Coffee 06:21:39 04/24/03 (4)
- You clammed up from the beginning. - jj 18:32:08 04/24/03 (3)
- Re: You clammed up from the beginning. - Jitter_by_Coffee 10:01:57 04/25/03 (0)
- Re: You clammed up from the beginning. - Jitter_by_Coffee 09:48:41 04/25/03 (1)
- No, there was no chance for a dialog - jj 21:56:46 04/25/03 (0)
- Re: Answers are good. Got some? - Jitter_by_Coffee 14:39:35 04/20/03 (42)
- Re: Answers are good. Got some? - john curl 22:48:02 04/20/03 (36)
- Re: Answers are good. Got some? - Jitter_by_Coffee 06:24:44 04/24/03 (4)
- Retract that false statement about me immediately. - jj 18:30:29 04/24/03 (3)
- crybaby., - Jitter_by_Coffee 09:58:15 04/25/03 (0)
- Re: Retract that false statement about me immediately. - Jitter_by_Coffee 09:51:51 04/25/03 (1)
- You have no idea what my "opinion" is, I hope - jj 19:27:23 04/29/03 (0)
- Perhaps you should look to what you support - jj 23:46:55 04/20/03 (30)
- Re: Perhaps you should look to what you support - john curl 22:33:16 04/21/03 (23)
- Euphonic is not the same as accurate... - jj 00:37:05 04/22/03 (22)
- Re: Euphonic is not the same as accurate... - john curl 10:00:09 04/22/03 (21)
- Several comments..... - jj 18:56:57 04/22/03 (20)
- Re: Several comments..... - john curl 21:54:53 04/22/03 (19)
- Indeed. You like LP.... Sometime, come hear my LP setup. - jj 23:30:54 04/22/03 (18)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - john curl 23:45:27 04/22/03 (17)
- Half and half, John, Half and Half... - jj 21:58:21 04/23/03 (0)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - Mr. Morello 14:58:50 04/23/03 (13)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - john curl 16:27:51 04/23/03 (12)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - Mr. Morello 16:33:47 04/23/03 (11)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - john curl 22:28:49 04/23/03 (10)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - Mr. Morello 23:47:25 04/24/03 (7)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - john curl 00:17:25 04/25/03 (6)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - Mr. Morello 05:06:54 04/25/03 (5)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - john curl 14:26:20 04/26/03 (4)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - Mr. Morello 14:37:26 04/27/03 (3)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - john curl 15:50:02 04/27/03 (2)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - Mr. Morello 00:38:48 04/28/03 (1)
- Re: Indeed. You like LP.... Sometime, come hear my LP setup. - john curl 09:05:04 04/28/03 (0)
- Double-blind is NECESSARY - jj 19:04:57 04/24/03 (1)
- Err, necessary in THIS CONTEXT... not for preferences... - jj 19:05:36 04/24/03 (0)
- Re: Could this quote explain some of your preferences - theaudiohobby 09:05:17 04/23/03 (0)
- Re: Could this quote explain some of your preferences - theaudiohobby 09:03:51 04/23/03 (0)
- Re: Perhaps you should look to what you support - john curl 10:07:30 04/21/03 (5)
- Jitter's comments on testing are useful how? - jj 21:18:28 04/21/03 (4)
- Re: Jitter's comments on testing are useful how? - Jitter_by_Coffee 06:12:44 04/24/03 (3)
- You haven't raised a single "known weak point" that anybody's published on - jj 18:25:41 04/24/03 (2)
- Re: You haven't raised a single "known weak point" that anybody's published on - Jitter_by_Coffee 10:11:24 04/25/03 (1)
- Short memory, eh? - jj 18:45:31 04/25/03 (0)
- Really? I've got 50 or 60 published papers. Let's see yours. - jj 19:17:43 04/20/03 (4)
- Re: Really? I've got 50 or 60 published papers. Let's see yours. - Jitter_by_Coffee 06:27:08 04/24/03 (3)
- Retraction? Yes, you owe me several now. - jj 18:27:52 04/24/03 (2)
- Re: Retraction? Yes, you owe me several now. - Jitter_by_Coffee 10:12:33 04/25/03 (1)
- And I'm still waiting. - jj 18:41:35 04/25/03 (0)