ASTM E296-1970(2004) Standard Practice for Ionization Gage Application to Space Simulators《用于空间模拟器的电离压力计的标准实施规程》.pdf
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1、Designation: E 296 70 (Reapproved 2004)Standard Practice forIonization Gage Application to Space Simulators1This standard is issued under the fixed designation E 296; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides application criteria, definitions,and supplemental information to assist the user in obtainingmean
3、ingful vacuum ionization gage measurements below 101N/m2(103torr) in space-simulation facilities. Since a varietyof influences can alter observed vacuum measurements, meansof identifying and assessing potential problem areas receiveconsiderable attention. This practice must be considered infor-matio
4、nal, for it is impossible to specify a means of applying thevacuum-measuring equipment to guarantee accuracy of theobserved vacuum measurement. Therefore, the users judg-ment is essential so that if a problem area is identified, suitablesteps can be taken to either minimize the effect, correct theob
5、served readings as appropriate, or note the possible error inthe observation.1.2 While much of the discussion is concerned with theapplication of hot-cathode ionization gages, no exclusion ismade of cold-cathode designs. Since a great deal more expe-rience with hot-cathode gages is available and hot
6、-cathodedevices are used in the majority of applications, the presentemphasis is fully warranted.1.3 The values stated in inch-pound units are to be regardedas the standard. The metric equivalents of inch-pound unitsmay be approximate.2. Referenced Documents2.1 ASTM Standards:2E 297 Methods for Cali
7、brating Ionization Vacuum GageTubes33. Terminology3.1 DefinitionsThe following definitions are necessary tounderstanding meaningful application of ionization-typevacuum-measurement devices and are useful in differentiatingbetween pressure, density, and flux measuring devices forproper application an
8、d interpretation of low-density molecularmeasurements.3.1.1 Blears effectthe reduction of the partial pressure oforganic vapors within the envelope of a tubulated ionizationgage below the partial pressure that would prevail in theenvelope with a tubulation having infinite conductance.3.1.2 controlle
9、d-temperature enclosed gagean enclosedgage in which the envelope is maintained at nearly uniformconstant temperature by suitable means.3.1.3 enclosed ionization gagean ionization gage forwhich the ion source region is enclosed over at least 0.95 3 4p steradians about the center of the region by an e
10、nvelope at aknown temperature with only a single opening such that allmolecules entering the ion source region must have crossed aplane located outside this region.3.1.4 equivalent nitrogen concentrationthe quantity ob-tained when the ion-collector current of a nude gage (inamperes) for the gas in t
11、he system is divided by the concen-tration sensitivity of the gage for nitrogen. This sensitivity isdefined as the ratio of gage ion collector current in amperes tomolecular concentration in molecules per cubic metre ofnitrogen under specified operating conditions.3.1.5 equivalent nitrogen flux dens
12、itythe quotient of thecurrent output of an enclosed vacuum gage operating underspecified conditions divided by the molecular flux sensitivityfor nitrogen.3.1.6 equivalent nitrogen pressure:3.1.6.1 For a nude gage, equivalent nitrogen pressure isobtained by multiplying the equivalent nitrogen concent
13、rationby kTwhere k is the Boltzmann constant and T is the meanabsolute temperature of the walls from which the gas mol-ecules travel to the ionizing region of the gage, averaged asnearly as possible on the basis of relative molecular flux.3.1.6.2 standard equivalent nitrogen pressurefor a nudegage,
14、the value of the equivalent nitrogen pressure is obtainedwhen T = 296K (or standard ambient temperature) is used inthe factor kT.3.1.6.3 For a tubulated gage, the equivalent nitrogenpressure in newton per square metre is obtained by dividing theion collector current in amperes for a given gas by the
15、 pressure1This practice is under the jurisdiction of ASTM Committee E21 on SpaceSimulation and Applications of Space Technology and are the direct responsibilityof Subcommittee E21.04 on Space Simulation Test Methods.Current edition approved Sept. 1, 2004. Published September 2004. Originallyapprove
16、d in 1966. Last previous edition approved in 1999 as E 296 70 (1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM
17、website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.sensitivity of the gage in amperes per newton per square metrefor pure nitrogen under specified operating conditions.3.1.7 gage backgroundthe part of the indicated io
18、n col-lector current produced by phenomena other than ions formedin the gas phase arriving at the collector.3.1.8 gage limita pressure or concentration indicationfour times the background.3.1.9 ionization gagea vacuum gage comprising a meansof ionizing the gas molecules and a means of correlating th
19、enumber and type of ions produced with the pressure orconcentration of the gas. Various types of ionization gages aredistinguished according to the method of producing the ion-ization.3.1.9.1 cold-cathode ionization gagean ionization gage inwhich the ions are produced by a cold-cathode gas discharge
20、,usually in the presence of a magnetic field.3.1.9.2 hot-cathode ionization gagean ionization gage inwhich ion production is initiated and sustained by electronsemitted from a hot cathode.3.1.10 molecular flux densitythe number of moleculesincident on a real or imaginary surface per unit area per un
21、ittime. The unit is molecules per second per square centimetre.3.1.11 molecular flux sensitivitythe output current of anenclosed vacuum gage per unit molecular flux density underspecified gage operating conditions and random particle mo-tion.3.1.12 nude ionization gagean ionization gage for whichthe
22、 center of the ion source region is exposed to directmolecular flux (from surfaces not forming part of the gage) inall directions except for a solid angle less than 0.05 3 4 psteradians (determined by the parts of the gage head). Nostructures shall be within one sensing element diameter of anypart o
23、f the sensing element unless similar structures are presentduring calibration.NOTE 1The solid angle subtended by a circular disk of radius r withaxis passing through the center point of the solid angle at a distance y fromthe disk is given as follows:v52 p1 2 y/y21 r2!1/2# (1)For v = 0.05 3 4p , the
24、 distance y must equal 2.07 r, a valuewhich should be easily attainable for typical ionization gageelectrodes mounted on a circular base of radius r.3.1.13 orifice ionization gagean enclosed gage containinga single orifice or port having a length less than 0.15 of itsdiameter such that molecules fro
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