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Isolated variable resistor function?

G

George Herold

Jan 1, 1970
0
  In refrigerators the cold plate is located in vacuum. If the relay
is not hermetically sealed, I'd expect its interior to get pretty much
evacuated while the main vacuum can is pumped. If it doesn't, the
interior probably cools via the metallic parts, so that the residual
gas condenses on the metal surfaces where the surface tension makes
the liquid to spread rather uniformly before it freezes. The frost
layer cannot be thick, the solid volume is maybe 700 times less than
the gas volume. Still, you made a good point.

  I find it amazing that the latching mechanism still works there,
it's based on what, a permanent magnet?

  Regards,
                 Mikko

Well permanent magnets like the cold... it's heat that kills 'em.

Any reason they shouldn't work in a nice dry exchange gas.. N2 or
He?
It'd be cool to put a switch down the bottom of a probe.
(Do you use through hole? Thermal expansion and all.)


George H.
 
G

George Herold

Jan 1, 1970
0
  They indeed seem to.

  Do you happen to know any high-frequency ferrites which would
survive cryo temperatures, BTW? Every one I have tried seem to
effectively turn into an air core in LHe. They must exist, as
evidenced by Pamtech circulators. There are some powdered iron and
nanocrystalline cores for lower frequencies, but I know nothing off-
the-shelf which would work for RF.

  Regards,
                 Mikko

Wow.. that's interesting. Do the ferrites still work at lower
frequencies?
Do they "frezze out" at 77K or only much lower?

George H.
 
B

Bill Sloman

Jan 1, 1970
0
Western Electric wouldn't sell the ones that were used by the Bell
System. WE had an anti-sales department whose job it was to convince
outsiders that they didn't want to buy WE parts.

And Charlie says, from first-hand experience, that they weren't very
reliable in exchange service. If Bell Labs couldn't get it right, why
would you expect some small reed manufacturer to get it right?

Charlie wasn't talking about a Bell system, but a GTE (General
Telephone and Electric Company system. GTE was the largest independent
telecom company in the US - number two, and trying harder without
access to Western Electric parts, if your claim is to be believed.
But the market for the little DPDT telecom relays is huge. Explain
that.

Why should I bother? And define "huge".
Useless fathead. You know everything and do nothing.

I certainly don't know everything. There are quite a few subject where
I know more than you do, but so do a lot of other people.

And I'm not completely inert. Presumably you'd be happier if I didn't
post stuff here, and I'd probably be happier if I had more rewarding
things to do with my time, but my current situation isn't rich in
activities for which I get rewarded. I really ought to get on with
building the low distortion oscillator, but the potential rewards are
too far off to get me going right now.
 
J

Jamie

Jan 1, 1970
0
Bill said:
Those failure rates strongly suggests that you were abusing the
contacts, whether you knew it or not.




But reed relays were invented by Bell Labs, for the telecom business,
and were very. very reliable when used carefully.




But you can't tell us which reeds, or why they were supposed to be
suitable for your articular job.




It's actually "dry" switching. The threshold is something like 100mA.




Not strange. Farnell's catalogue now has a lot more solid state
switches in the relay section than it did thirty years ago - the
market for reed relays has shrunk and that does drive manufacturers
out if business.




Experience is a hard school but fools will learn in no other. I'm not
that kind of fool. I try to anticipate that kind of experience by
reading about what has happened to other people and how they coped
with it - it's what academic engineering is all about. You don't seem
to do that kind of reading, nor understand why other people would want
to, and insist that your own experience, limited and specialised as it
is, is worth more than the - admittedly imperfectly - documented
experience of the rest of the world.
Spoken like a typical leach.

That only proves what I said early about you (shoulder Educated)

Jamie
 
B

Bill Sloman

Jan 1, 1970
0
BillSlomanwrote:



  Spoken like a typical leach.

  That only proves what I said early about you (shoulder Educated)

Jamie really is a moron. Science - and western culture generally - is
all about us building on the published experiences of our
predecessors. Jamie seems to think that the only honest approach is
for us to each re-invent the wheel for ourselves.

For some bizarre interpretation of "honesty" he may be right, but it's
an impractical approach, and only a moron could fail to appreciate
that he too exploits the experience of his predecessors. He probably
doesn't exploit it often enough, which would make him a rather
unsatisfactory engineer, even if he were a particularly talented
tinkerer (and he's not posted anything that would lead us to think
that either).
 
Most materials get stronger at cryo tempeartures.

Stronger? ...or harder/more brittle? Define "stronger"?
I suppose differential expansion could cause problems, but I doubt it
would bother one of these little relays.

I remember playing with LN2 in physics lab, after all the work was done. I
dropped a banana cable into the LN2, just as the lab assistant came by. After
removing it, the plastic banana insulator exploded - physics lessons in
differential expansion. ;-)
 
B

Bill Sloman

Jan 1, 1970
0
Does taking years to not-finish an oscillator, that no-one wants, make
you a satisfactory engineer?

It makes me a rather dilatory hobbyist. I'm not sure that nobody will
want the oscillator when I get it put together and working - it's just
that there isn't a single obvious application.

If the simulations are to be believed, it will be able to deliver a
remarkably clean sine wave of stable amplitude over a significant
range of frequencies, and you will be able program the frequency
electronically with a voltage in the range +/10V.

I've had applications from time to time that could have used something
like that.
 
The usual measures, compressive and tensile strength.

There are many meanings of "stronger". Often something that is more pliable
will be "stronger", in some measure. Hardness can be a weakness. ;-)
Thermal shock breaks things. Pour some boiling water into a glass...
it may well break. That's not a cryogenic issue.

Delta-T
 
M

Mr Stonebeach

Jan 1, 1970
0
Wow.. that's interesting.  Do the ferrites still work at lower
frequencies?

No, mu disappears completely.
Do they "frezze out" at 77K or only much lower?

I use a LHe dipstick, but haven't kept track at which height (iow.
temperature) various cores die. From my vague memories I'm inclined to
say some cores might keep functioning in LN2.

Regards,
Mikko
 
G

George Herold

Jan 1, 1970
0
  No, mu disappears completely.


  I use a LHe dipstick, but haven't kept track at which height (iow.
temperature) various cores die. From my vague memories I'm inclined to
say some cores might keep functioning in LN2.

  Regards,
                  Mikko

Googling low temperature and ferrites I found a paper by Bickford,
Rev, Mod. Phys. 1953 "Low Temperature Transformation in
Ferrites" (I'm still trying to read it, terrible copy that I found on
the web.)

George H.
 
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