smlg1015@uxa.cso.uiuc.edu (01/29/90)
Dear sci.electronics: Can somebody familiar with vacuum technology tell me to what the terms, "high vacuum","ultra high vacuum", and "super high vacuum" correspond? In particular, 10E-7 particles per cm3 corresponds to which category? This is said to be the density of an interstellar dust cloud. What's the best that can be achieved in the lab? Thanks, smlg1015@uxa.cso.uiuc.edu
ee5391aa@hydra.unm.edu (Duke McMullan n5gax) (01/30/90)
Vacuum terminology? That's when you say that something "sucks".
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"So much karst; so little time...."
Duke McMullan n5gax nss13429r phon505-255-4642 ee5391aa@hydra.unm.eduberryh@udel.edu (John Berryhill) (01/30/90)
In article <108800006@uxa.cso.uiuc.edu> smlg1015@uxa.cso.uiuc.edu writes: > >In particular, 10E-7 particles per cm3 corresponds to which category? >This is said to be the density of an interstellar dust cloud. What's >the best that can be achieved in the lab? I think the record is in the low 10^-9 mm of Hg range. -- John Berryhill "Boil that dust speck!" 143 King William, Newark DE 19711
henry@utzoo.uucp (Henry Spencer) (01/30/90)
In article <9505@nigel.udel.EDU> berryh@udel.edu (John Berryhill) writes: >>In particular, 10E-7 particles per cm3 corresponds to which category? >>This is said to be the density of an interstellar dust cloud. What's >>the best that can be achieved in the lab? > >I think the record is in the low 10^-9 mm of Hg range. 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 residual gas onto the walls), the theoretical limit is somewhere around 10^-21, although measuring a vacuum that hard is beyond current equipment. This is from memory, so I may have botched details. (I was interested in ultrahigh-vacuum technology some years ago, but it's been a while.) O'Hanlon's "A User's Guide to Vacuum Technology" (1980) gives the following ranges of vacuum, pressure in Pascals (101323.2 Pa = 760mmHg): low 1e5 > P > 3.3e3 medium 3.3e3 > P > 1e-1 high 1e-1 > P > 1e-4 very high 1e-4 > P > 1e-7 ultrahigh 1e-7 > P > 1e-10 extreme ultrahigh 1e-10 > P and notes that "high" often is used to cover "very high" as well. Those dust-cloud density numbers are talking about solid particles, not gas molecules. The old rule of thumb for interstellar gas is about one hydrogen atom per cc, although I think that's been revised down a bit. -- 1972: Saturn V #15 flight-ready| Henry Spencer at U of Toronto Zoology 1990: birds nesting in engines | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
knudsen@cbnewsd.ATT.COM (michael.j.knudsen) (02/03/90)
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."
fcr@saturn.wustl.edu (Frank C. Robey X5569) (02/05/90)
In article <13027@cbnewsd.ATT.COM> knudsen@cbnewsd.ATT.COM (michael.j.knudsen) writes: > ... >Could someone tell me what is the format definition of a Pascal? >Something simple, like a dyne/cm2? According to my Thermo' book 1Pa = 1 Newton/m^2. > ... >As the above shows, it is almost but not quite a power of ten >times one atmosphere. Also in my Thermo' book, 1 atm (std) = 101,325 Pa. 1 bar = 100,000 Pa. My book is C 1976, so there may have been minor changes in the std atm since then. Frank Robey fcr@saturn.wustl.edu fcr@wuee1.wustl.edu Electronic Systems and Signals Research Laboratory Washington University- St. Louis
henry@utzoo.uucp (Henry Spencer) (02/06/90)
In article <13027@cbnewsd.ATT.COM> knudsen@cbnewsd.ATT.COM (michael.j.knudsen) 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... > >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 :-). Helium seepage through glass is so rapid, actually, that the interior of most any glass apparatus is in equilibrium with atmospheric helium. The glass tubes have had that helium in them essentially from the start; it's not something that would happen gradually over a period of years. Just as well that there isn't much of it in the air. (There wouldn't be any if not for radioactive decay -- that helium started out as alpha particles from radioactive elements in the Earth's crust.) >Could someone tell me what is the format definition of a Pascal? A Pascal is a newton per square meter, i.e. the obvious SI pressure unit. Fortuitously, one atmosphere is almost exactly 100 kiloPascals. -- SVR4: every feature you ever | Henry Spencer at U of Toronto Zoology wanted, and plenty you didn't.| uunet!attcan!utzoo!henry henry@zoo.toronto.edu