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Re: Solving the Floating-Point Goldilocks Problem!

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jmfbahciv wrote
> sidd wrote
>> jmfbahciv wrote

>>> How did you find the disappearing shorts?

>> Depended on the specific fault. First, log the fault. Then find,
>> isolate and monitor and immediately set one or more recorders to
>> monitor them. Back in those days, this might be a chart recorder, or
>> a grad student.Then you consulted the logbook, pored over heavily
>> modified schematic and illegible scrawlings. You had, of course,
>> measured resistances and  impedances of all legs of each circuit at
>> room temperature, when the cryostat was open, and you had
>> periodically measured many things as the cooldown proceeded. You had
>> data on the composition and behavior of the various bits of your
>> wires. From these and the currently measured values, you could often
>> make an intelligent guess at the location. Before you warmed up the
>> cryostat you could do further testing...if for example if i push a
>> current through the short, which bits of the cryostat warms up ? or
>> if a coax line, you might break out the storage scope and polaroid,
>> and do TDR off the line to get an idea of distance to the fault.

> Distance?!  Were there loops?

>> After you were done with any lo-T diagnosis, you warmed up the
>> cryostat watching the fault all the way to room-T. You have
>> thermometers and sensors all thru the cryostat, you might pause
>> along the route if you saw sumpn interesting...eg circuit
>> parameter changed when this bit of the circuit warmed through
>> superconducting transition temperature...and such. Along the
>> warmup, you take advantage of the hysteresis, in that the innardz
>> of the cryostat cool the slowest and warm the slowest, so you are
>> applying different thermal (and thus mechanical) gradients to the
>> cryostat and you know which parts are being stressed in which order;
>> this order is different during cool down and warmup.

>> Disappearing faults disappear differently.The manner of their
>> vanishing often betrays whence they came.

> Ah!  That would be useful.

>> When all else fails, you rip out and replace, an operation
>> that (in some cases) can take months.

> Thanks.  No wonder physicists love their gadget (not to be
> construed as a slight).

> how does one learn all those tricks such as "disappearing differently"?

Same way you do any engineering, observe its behaviour carefully.

> Wouldn't the behaviour be unique to each cryostat?

You mean each copy or each basic technology ?

> Or are they constructed so alike that working on one trains
> you to be able to do the same diagnoses on another.

Not between technologys. 

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Re: Solving the Floating-Point Goldilocks Problem! jmfbahciv <See.above@aol.com> - 2011-09-08 14:10 +0000
  Re: Solving the Floating-Point Goldilocks Problem! sidd <sidd@situ.com> - 2011-09-08 14:08 -0400
    Re: Solving the Floating-Point Goldilocks Problem! jmfbahciv <See.above@aol.com> - 2011-09-09 15:21 +0000
      Re: Solving the Floating-Point Goldilocks Problem! "Rod Speed" <rod.speed.aaa@gmail.com> - 2011-09-10 06:00 +1000

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