Re: "mild arthritic changes" indeed

On Fri, 23 Jan 2009 23:44:26 GMT,
mroberds@xxxxxxxxxxxxxxxx wrote in
<uDsel.171$B_1.117@xxxxxxxxxxxx>:

Mike Andrews <mikea@xxxxxxxxxxxx> wrote:
There has been a thread on that in the Glowbugs list which has been
_quite_ sobering, as well as another tale from the gent who worked at
the HV capacitor plant.

Link?

: OK... By Special Request, here's the story.
:
: One item we made was packaged high voltage, low current power
: supplies. They ranged from maybe 1000 VDC @ 5 MA,
: to the Big Honkin' Mutha, a 100 KV, 100 MA job, built in a can of
: mineral oil to keep 'em from arcing over internally.
:
: These things were BIG... the big one had to be moved around the
: Quality Control Lab with a fork lift truck.
:
: I tried repeatedly to find out what they used these grotesque things
: for, but I never got a good answer. Just the same tho, we
: had one customer who bought maybe ten of them per year, and returned
: the old ones (blown) for rebuilding. I was vaguely
: told this outfit used them for powering industrial X-ray tubes for
: some purpose.
:
: Testing something like this is a major undertaking.
:
: For one thing, we had to constantly monitor the weather. A wet bulb /
: dry bulb thermometer was used to check the humidity
: (the plant wasn't air conditioned). If humidity was over about 50 -
: 60 percent, high voltage testing was put off that day; if you
: tried it, you'd get an arc from the 18" high insulator that held the
: output corona ball, and it would zap into plumbing, building
: structural steel, etc. I've seen these supplies throw a six foot
: spark to find ground.
:
: We didn't have a high voltage cage big enough to fit these monsters
: into... so, we'd put it in the center of the floor in the
: basement, and rope off a danger area, ten feet around it.
:
: We obviously didn't wanna get anywhere near these things when they
: were in operation. The output voltage meter was
: something built in house; somewhere, they found a meter movement that
: was about 12 by 16 inches, and could be easily
: read thru binoculars! We had a meter multiplier resistor bank built
: on a *** of plywood, and the resistors inside of glass
: tubes filled with mineral oil to keep them from flashing over.
:
: Primary power was applied through a Variac with a LONG cord!
:
: One day the humidity was low enough, meaning that we could probably
: get thru it with maybe a half dozen tries before we got
: there without an arc popping the breaker, requiring us to start over!
:
: We set up the rope around the danger area, and I put the Variac
: behind a heft steel beam that was holding the building up. I
: sat behind it, reasoning that an arc would have to take out the beam
: before it could get ME!
:
: It had been a marginal morning... my nerves were shot; I'd get the
: supply to 60 or 70 KV and then we'd get an arc to ground
: that sounded like a rifle shot.
:
: It happened to be a Friday... Pay Day.
:
: I was hunched behind the beam, slowly inching up the Variac, and I
: almost jumped out of my skin... someone had come up
: behind me and touched my shoulder.
:
: It was the boss's secretary. It was her habit on pay day to walk
: around the plant, handing out the pay checks in person to each
: employee. It was always accompanied by a smile on her plain, chubby
: face, and a soft "Thank You".
:
: She handed me my check, and smiled as I nervously stuffed it into my
: pocket , and returned my attention to cranking more AC
: into the supply. She wandered away.
:
: I was almost to 90 KV when I near wet my pants... somehow, one of
: the danger zone ropes had been removed, and the secretary
: was walking straight toward the power supply!
:
: I yelled a warning, but the noise level was pretty high and she
: didn't hear. I slammed my hand down on the breaker, dumping the
: AC to the power supply... but it contained filter caps. It would
: take a while for the bleeder resistors to discharge those caps!
:
: She did a left turn about 3 feet from the supply, headed toward
: another employee.
:
: The electrostatic charge around the beast caused the hair on the
: right side of her head stand up almost straight!
:
: She never noticed the danger she was in... she kept walking, and
: raised her hand to smooth her hair down... and she walked away
: from the power supply.
:
: It never touched her!!! She never knew how close to disaster she came.
:
: Thoroughly shaken, me and the other techs put the ropes back up, and
: started powering up again.
:
: This time, we got less than halfway there... it threw about a 5 foot
: arc at about 50 KV!
:
: WHY it didn't zap her I'll never know...
:
:
: Mr. T., W9LBB

Oh, and it's glowbug gear, usually: a couple of Big Whompin' Eimac
tubes

Given the cost pressures in the medical world, I'd guess "Svetlana
tubes rebuilt in East Elbonia", but that's me.

Or the .cn "equivalent", though if it's on a maintenance contract, I
wouldn't be at all surprised to to see gen-you-wine Eimac or Machlett
or Burle toobs in the final sockets. And if I owned an MRI used for
production work, it damn well would be on a maintenance contract.

putting out RF to polarize the spins, and then a very sensitive RX
to listen for echoes. Sometimes, AIUI, it's 572Bs or something of
the sort, sometimes it's a pair of 4CXwhatever or 3CXfoo.

Now I am picturing some medical tech looking at an SWR meter. "OK, now
uncurl the fingers on your good hand about an inch... right there!
1.05:1, that's great!" Or: "We can't get it below 3:1 for some reason.
We're going to try to improve the impedance match. Here's some water;
swallow as many of these black pills as you can." "Um, what are these,
exactly? They're kinda heavy." "Ferrite."

I really don't know the details, but suspect that the widgetry includes
a _really_ good autotuner.

Anyone else here read about the cold solder joint in the LHC in the
last week or two? Apparently it was in a soldered link between two
superconducting magnets, and caused at least one to quench from
resistive heating.

I wonder if it was done with the New Improved Lead-Free It Works Really
Great No Seriously It Does* solder.

Yes, I think it was. It's in .eu, after all, and so ROHS is A Major
Concern -- much more so than It Has To Work.

(* Well, you don't have to use it on anything that actually *has* to
work, like telecom, military, etc. You have to use it on consumer
stuff, though, so it can fail sooner, thereby increasing sales of
replacement gear^W^W^W^W^Wsaving the planet. )

See Above.

They lost something like a mass-ton of He out the dump pipe. Ouch!

"What's wrong?" "Well, the magnetizing current shot way up, and
everybody in control room B sounds like a chipmunk."

Actually, the I would drop at a quench, wouldn't it? The magnet stops
being a superconductor and actually exhibits resistance, which induces
an IR drop. I think I saw a pic of the dump duct a few months ago. If it
was the one I thought it was, it's about a meter in diameter. I wonder
how long it takes to dump a mass ton of He gas through a pipe that size.

--
.... at the end of the conversation, the guy said "Thanks a lot for
reporting this. If you need more details on our anti-spam policies,
just hit 'refresh' on the URL you reported."
.

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