Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!samsung!zaphod.mps.ohio-state.edu!wuarchive!mit-eddie!rutgers!att!cbnewsd!knudsen
From: knudsen@cbnewsd.ATT.COM (michael.j.knudsen)
Newsgroups: sci.electronics
Subject: Re: Vacuum Terminology
Summary: Tubes, Pascals
Message-ID: <13027@cbnewsd.ATT.COM>
Date: 2 Feb 90 21:22:05 GMT
References: <108800006@uxa.cso.uiuc.edu> <9505@nigel.udel.EDU> <1990Jan30.045241.20029@utzoo.uucp>
Organization: AT&T Bell Laboratories
Lines: 34

In article <1990Jan30.045241.20029@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes:
> Not even close.  Glass apparatus peters out around 10^-10 mm because of
> atmospheric helium seeping through the glass (!), metal goes on for
> several more orders of magnitude with hydrogen seepage an increasing
> nuisance.  With lots of liquid helium for cryogenic "pumping" (freezing

Hmmm. I collect and restore antique radios, and have always been impressed
with how well tubes made in the 1920s (that's 75 years ago!) are still
holding vacuum, at least judging by how well they still perform.
A few are gassy and have problems, but often these are relatively "new"
ones from the '40s and '50s.
Many of the late '30s tubes were metal instead of glass, mostly
to get better RF shielding -- according to Henry these should hold
their vacuum even longer, tho they don't look nearly as nice :-).

I guess tubes fit into the "medium high" vacuum range.

> ranges of vacuum, pressure in Pascals (101323.2 Pa = 760mmHg):

Could someone tell me what is the format definition of a Pascal?
Something simple, like a dyne/cm2?
(I know that kg/m2 offends the purists -- mass -vs- force --
tho that's what most European plain-folks use.  They have recently
discovered newtons, though.)

As the above shows, it is almost but not quite a power of ten
times one atmosphere.  I've been trying to trace down this unit
ever since my wife's GM X-car listed tire pressures in KPa
but not PSI -- amazing how far GM went in trying to impress the
US Govt back when it was pushing metric units.
-- 
Mike Knudsen  knudsen@ihlpl.att.com   (708)-713-5134
"Round and round the while() loop goes;
        Whether it stops," Turing says, "no one knows."