Isolated variable resistor function?

Most materials get stronger at cryo tempeartures.

I suppose differential expansion could cause problems, but I doubt it would bother one of these little relays.

yeah, that's true but just don't perform any tensile motion on them. Also I question if the seal would maintain at those temps?

Jamie

Ah, but a PM works better when they get colder..

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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.

-- Bill Sloman, Nijmegen

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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?

But the market for the little DPDT telecom relays is huge. Explain that.

Useless fathead. You know everything and do nothing.

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

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.

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

George H.

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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.

Why should I bother? And define "huge".

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.

-- Bill Sloman, Nijmegen

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Spoken like a typical leach.

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

Jamie

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).

-- Bill Sloman, Nijmegen

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

Stronger? ...or harder/more brittle? Define "stronger"?

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. ;-)

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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.

-- Bill Sloman, Nijmegen

The usual measures, compressive and tensile strength.

Thermal shock breaks things. Pour some boiling water into a glass... it may well break. That's not a cryogenic issue.

There are many meanings of "stronger". Often something that is more pliable will be "stronger", in some measure. Hardness can be a weakness. ;-)

Delta-T

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.