Yeah, this puts the heat on the phones.

On 26 March 2012 18:52, Paul Edwards <[log in to unmask]> wrote:

> Thanks Bob...
>
> This puts the meat on the bones...
>
> Paul
>
> Paul Edwards
> Process/Quality Engineering
> Surface Art Engineering
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
> Sent: Sunday, March 25, 2012 8:57 AM
> To: [log in to unmask]
> Subject: [TN] More Information on Casini Tin Whisker Investigation
>
> > From: Leidecker, Henning W. (GSFC-5600)
> > Sent: Friday, March 23, 2012 7:55 PM
> >
> > Subject: RE: Any Information on Casini Tin Whisker Investigation?
> >
> > The group that did this investigation met today to assign tasks for the
> writing of the final report.  So, the final report is "in progress" but it
> is not yet released.  (I am one of this group.)
> >
> > Each of the three radio-isotope generators has a high-rail at V+ and a
> low-rail at V-, with a resistor bridge that establishes a connection to
> ground, held between V+ and V-.  One of the three radio-isotope generators
> has shown a sequence of soft-shorts: it is still able to deliver its power,
> but it is shifting its off-set from ground -- this has not been a problem,
> yet.  This behavior has been seen on a few other radio-isotope generators:
> it is probably not of direct interest to most industries.
> >
> > The CAPS instrument has show a sequence of soft-shorts in distinct
> locations.  Each has 'cleared' after various durations of elapsed times.
>  Another has just appeared after the recent turn-on.  The instrument is
> still working, and the shorts do not draw so much current as to cause harm.
>  But no one likes these, and folks wonder whether one of these will jump to
> a "hard short".  The specific concern is that such a hard short might harm
> the power system and thus kill the other instrument.
> >
> > We never found an explanation for these radio-isotope events, or for the
> soft shorts in CAPS, that had the sweep smell of "Yes!  That has to be the
> reason!"  We have found tin whiskers growing from tin-plated transformer
> cans of the precise type used in the CAPS, when we inspected similar items
> still on the ground, and we showed that the shorting/clearing behavior of
> these whiskers were consistent with the observed "soft shorts" and also the
> time-dynamics of the coming/going of these soft shorts.  So, we supposed
> that tin whiskers were a possible cause.  While we considered many
> alternatives, some of which were also plausible, it was the whiskers that
> seems the least objectionable.
> >
> > See the "tin whiskers (and other metal whiskers)" web site run by GSFC:
> http://nepp.nasa.gov/WHISKER/
> > This site illustrates many many horrors that have been rigorously
> established to be caused by metal whiskers.
> >
>
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