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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: But seriously, folks... posted by Charles Hansen on June 2, 2003 at 11:53:09:
""why in the world do you want to go from an oven at 423 K to a LN2 bath at 77 K???""As a screening process...and it sucks waiting for the parts to get to room..
What happens when we dunk, is that the ln2 actually does not touch the parts when they are hot..The heat radiation boils the liquid without touching it...Where the most heat transfer occurs, is when the parts are quite cold already, and the liquid actually touches the part..You can actually see this occur..The liquid boils at one rate for a while...then at the sweet point, the boiling really becomes violent, then drops off. I've no idea what temp that occurs at, though.. But, I do know that the same scenario occurs with parts that start at room temp..So the dunk doesn't care what the starting temperature is..(assuming a linear tce to 77K..)
""However, it has nothing to do with good sound.""
I know...I was hoping that somebody would have some experience with resistors and cryo..
""When cryo-ing parts, it is important to do it gradually. This is to avoid damaging the parts. The normal practice is to take things down over a 12 hour span (or so) to LN2 temperatures and then leave them there for few hours. Then they are slowly brought to room temperature again.
Dunking hot things in LN2 (or better yet liquid He at 4 K!) is a recipe for breakage due to thermal shock.""total agreement...BTW, we dunk into LN2, Helium is a gradual cooldown, cause the magnets are about 10 meters long and would have a problem with high rates..LN2 also costs about 32 cents per quart, liquid He about 50 dollars a liter..
""I am surprised that you found things that still worked after this kind of treatment.""Me too..it's hugely abusive..
""However, I am willing to bet that there is hidden damage on your parts. Perhaps in the form of micro-fractures in the coating that will allow oxidants into the interior of the part.""
So far, we've experienced no reliability problems..but what you say it valid...However, I'm not sure what the tce or thermal conductivity of the outer coating is..If the conductivity is high enough, and the tce very close to the base material, then the dunk won't cause damage...but I wouldn't bet my money on it..we never did high power visual on the units..but they work in the ring, very reliably..
Thanks for the reference, though...We farmed out the last 6000 units, and if we have a large quantity, they might be a good vendor..
Cheers, John
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Follow Ups
- Re: But seriously, folks... - jneutron 13:16:59 06/02/03 (0)
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