> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Poul-Henning Kamp
> Sent: Monday, January 25, 2010 2:48 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Low temperature coefficient capacitors for DMTD
>
> In message
> <ece7a93bd093e1439c20020fbe87c47fed2b80a...@altphyembevsp20.res.ad.j
> PL>, "Lux, Jim (337C)" writes:
>
> >
> In 1990, the conclusion of a polycarbonate film capacitor
> paper[1] stated, "both the orientation and crystal structure
> of PC (polycarbonate) film affects its mechanical properties
> and electrical dissipation factor". The paper was a cooperative
> investigation by the Jet Propulsion Laboratory and Electronic
> Concepts' film manufacturing division,
>
> Why would JPL study obscure production details of polycarbonate
> film capacitors in 1990, if they fell of the market six years earlier ?
Oh my.. a bit of research in Xplore finds that all the gory details were in the
very section I work in at JPL (we build radios for deep space missions)
Well, the original incident triggering the study was in 1978 on Voyager 2, when
they weren't able to get an uplink lock to the spacecraft. The telemetry from
the spacecraft indicated that the loop filter in the carrier tracking loop was
having problems, most likely from leakage across the 75 uF capacitor. They
figured out a workaround to estimate the best lock frequency using temperature
and Doppler estimates, and Voyager continues on its happy way out of the solar
system. (FWIW, the carrier tracking loop has a bandwidth of a few Hz, I think.)
In fact, my office mate says that the former occupant of the chair I am sitting
in as I type this spent months checking the best lock frequency of Voyager to
develop that estimation approach.
Frank Ott (a coworker who retired a couple years ago) did the failure analysis
and figured out a way to test the capacitors and published a paper in 1985
describing it, and that paper was the basis for the 1990 Yen and Lewis paper
cited in the white paper.
So, JPL actually did the studying in the 80s, right around when the market for
polycarbonate caps was going away.
Interesting conclusions in Ott's paper: "Conditions leading to a capacitor
failure can occur without voltage being applied. JPL believes the Voyager
in-flight failure occurred during six months of non-operation."
The actual reference (from IEEE Xplore) is:
"Effect of structure and morphology on thermal and electrical properties of
polycarbonate film capacitors"
Yen, S.P.S. Lewis, C.R.
Jet Propulsion Lab., California Inst. of Technol., Pasadena, CA, USA;
This paper appears in: Power Sources Symposium, 1990., Proceedings of the 34th
International
Publication Date: 25-28 June 1990
On page(s): 387 - 391
Meeting Date: 06/25/1990 - 06/28/1990
Location: Cherry Hill, NJ
ISBN: 0-87942-604-7
INSPEC Accession Number:4111725
Digital Object Identifier: 10.1109/IPSS.1990.145871
Current Version Published: 2002-08-06
Abstract
Research is reported to identify polycarbonate (PC) film characteristics and
fabrication procedures which extend the reliable performance range of PC
capacitors to 125°C without derating, and establish quality control techniques
and transfer technology to US PC film manufacturers. The approach chosen to
solve these problems was to develop techniques for fabricating biaxially
oriented (BX) 2 μm or thinner PC film with a low dissipation factor up to
140°C; isotropic dimensional stability; high crystallinity; and high voltage
breakdown strength. The PC film structure and morphology was then correlated to
thermal and electrical capacitor behavior. Analytical techniques were developed
to monitor film quality during capacitor fabrication, and as a result,
excellent performance was demonstrated during initial capacitor testing
---
And the paper's first paragraph says why JPL would do this:
In March 1978, a 78 uF PC capacitor failed in a receiver tracking loop filter
aboard Voyager I. This failure led to a series of investigations to duplicate
the failure mode, determine the failure mechanism and establish a viable
screening technique. The research was completed in 1982 [1-3]. Sporadic
failures of metalized 2 micron polycarbonate (PC) film capacitors in low
voltage high impedance circuits indicated lack of reliability above 100°C.
Although the failure mechanism was not identified, a ramp test was implemented
as a standard screening test[3], and 100°C was set as the upper temperature
limit for full rated voltage use. For 125'C applications, a 50% voltage
derating was recommended.
You can find the paper in NASA Technical Reports Server (NTRS) at
ntrs.nasa.gov... The record there says it's not copyrighted, but the electronic
copy I have has the IEEE copyright notice on it.
NTRS has another paper listed "Review of the NASA Voyager spacecraft
polycarbonate capacitor failure incident"
Summary: The premission failure of a Voyager spacecraft capacitor has
prompted an investigation into the use of polycarbonate capacitors in high
impedance circuits, during which capacitor failures were induced by thermal
cycling together with extended periods at high temperature. Measurement of
leakage path temperature coefficients indicates that there are two distinct
leakage types whose mechanisms are complicated by movement within the capacitor
during temperature changes. A novel system for pulse detection during capacitor
burn-in and ramp testing has proven to be beneficial.
Feb 1, 1985
IEEE Transactions on Electrical Insulation (ISSN 0018-9367), vol.
EI-20, Feb. 1985, p. 47-54.
Frank Ott, the lead author on the latter, retired about 2 years ago, and
coauthored a NASA Tech Brief on a technique for "determining internal
connections in capacitors" in 1986 (presumably from the same incident).
NPO-16499 and a "Capacitor Test System" (NPO-16485) which was a microprocessor
controlled system simultaneously monitoring 80 capacitors (which is how they
got those millions of hours).
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