1、 Reference number ISO 27894:2009(E) ISO 2009INTERNATIONAL STANDARD ISO 27894 First edition 2009-12-15 Vacuum technology Vacuum gauges Specifications for hot cathode ionization gauges Technique du vide Manomtres vide Spcifications pour les manomtres ionisation cathode chaude ISO 27894:2009(E) PDF dis
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5、TECTED DOCUMENT ISO 2009 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs
6、member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2009 All rights reservedISO 27894:2009(E) ISO 2009 All rights reserved iiiContents
7、Page Foreword iv Introduction.v 1 Scope1 2 Normative references1 3 Terms and definitions .2 4 Symbols and abbreviated terms 6 5 Principle of hot cathode ionization gauge7 6 Specifications for hot cathode ionization gauge to be provided by manufacturers7 7 Additional (optional) specifications for hot
8、 cathode ionization gauge to be provided by manufacturers10 8 Influences contributing to the measurement uncertainty with hot cathode ionization gauges 11 Annex A (informative) Typical Bayard-Alpert gauge with a glass envelope.14 Annex B (informative) Typical electrical connection of a Bayard-Alpert
9、 gauge 15 Annex C (informative) Problems with ionization gauges16 Bibliography18 ISO 27894:2009(E) iv ISO 2009 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing Intern
10、ational Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with
11、 ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical
12、 committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to
13、the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 27894 was prepared by Technical Committee ISO/TC 112, Vacuum technology. ISO 27894:2009(E) ISO 2009 All rights reserved
14、 vIntroduction Ionization gauges are commonly used in the measurement of high and ultra-high vacua. The collected ion current in this gauge is proportional to gas density, respectively pressure, at a known temperature in high and ultra-high vacua. The ionization of neutral gas particles is accomplis
15、hed by fast electrons. These electrons are either produced by a self-sustaining discharge or by an emissive cathode. In commercial ionization gauges, this emissive cathode is provided by a heated wire (“hot cathode”) emitting electrons by thermionic emission. Since ionization gauges with a self-sust
16、aining discharge by crossed electrical and magnetic fields show non- linearity in discharge current versus gas density, they are tedious to calibrate. For this reason, ionization gauges with “hot cathodes” exhibiting a more linear reading are the ones mainly used for the dissemination of the pressur
17、e scale in high and ultra-high vacua. For the dissemination of the pressure scale and a reliable measurement of high and ultra-high vacuum pressures by an ionization gauge, the relevant parameters and uncertainties must be given, and are described in this International Standard. It therefore complem
18、ents ISO/TS 3567 when using ionization gauges as reference standards. INTERNATIONAL STANDARD ISO 27894:2009(E) ISO 2009 All rights reserved 1Vacuum technology Vacuum gauges Specifications for hot cathode ionization gauges 1 Scope This International Standard defines terms relating to hot cathode ioni
19、zation vacuum gauges, and specifies which parameters are given by manufacturers of hot cathode ionization gauges and which measurement uncertainties have to be considered when operating these gauges. The reasons for this are as follows. a) This International Standard updates some terms and definitio
20、ns given in ISO 3529-3:1981. b) This International Standard specifies information for suitable laboratories to correctly calibrate vacuum gauges under high and ultra-high vacua, since ionization gauges with hot cathodes are often used as reference standards. This information consists of the relevant
21、 parameters and characteristics suitable for quotation in manufacturers instructions to users employing ionization gauges for traceable measurement of pressure under high or ultra-high vacua. c) This International Standard also lists those uncertainties associated with the measurement of pressure by
22、 the ionization gauge, which are known to be significant, and gives guidelines on how to evaluate them. It is possible that the list is not comprehensive for some current or future vacuum gauges. d) This International Standard complements ISO/TS 3567 and ISO/TS 27893 when using ionization gauges as
23、reference standards. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO/T
24、S 3567, Vacuum gauges Calibration by direct comparison with a reference gauge ISO/IEC Guide 98-3:2008, Uncertainty of measurement Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) ISO 27894:2009(E) 2 ISO 2009 All rights reserved3 Terms and definitions For the purposes of this
25、document, the following terms and definitions apply. 3.1 Definitions of components 3.1.1 gauge head gauge tube part of the gauge that is exposed to the vacuum NOTE 1 Adapted from ISO 3529-3:1981. NOTE 2 The gauge head of the hot cathode ionization gauge contains at least a cathode or filament, anode
26、, ion collector and the corresponding electrical vacuum feedthroughs. See Figure A.1 in Annex A. 3.1.2 control unit controller part of the ionization gauge which comprises the electrical circuits necessary to energize the tube, to control and measure currents or voltages, and, in some cases, to supp
27、ly power for degassing of tube elements NOTE 1 See Figure B.1 in Annex B. NOTE 2 This cancels and replaces the definition for “gauge control unit” in ISO 3529-3:1981. 3.1.3 integrated type active gauge type transmitter type gauge in which the tube and controller form one piece of equipment which may
28、 be separated for baking NOTE See Figure 1 a). 3.1.4 separated type passive gauge type gauge in which the tube and gauge controller are separate pieces of equipment connected by a cable NOTE See Figure 1 b). 3.1.5 single gauge one gauge in one piece of equipment NOTE See Figure 2 a). 3.1.6 combined
29、gauge more than one gauge in one piece of equipment NOTE See Figure 2 b). 3.1.7 envelope wall of metal or glass that encloses the operating elements of a vacuum gauge ISO 27894:2009(E) ISO 2009 All rights reserved 3a) Integrated type b) Separated type Key 1 controller 2 gauge tube 3 control unit 4 c
30、able Figure 1 Vacuum gauges; integrated and separated type a) One gauge in a body (single gauge) b) Two gauges in a body (combined gauge) Key 1 gauge tube 2 gauge tube (gauge 1) 3 gauge tube (gauge 2) Figure 2 Vacuum gauges; single and combined gauge ISO 27894:2009(E) 4 ISO 2009 All rights reserved3
31、.2 Definitions of physical parameters 3.2.1 sensitivity sensitivity coefficient S quantity given by () cc 0 e0 II S I pp = (1) where I e is the emission current; I cis the ion current, measured at pressure p; I c0is the ion current, measured at pressure p 0 ; p is the pressure; p 0is the residual pr
32、essure. NOTE This definition cancels and replaces the definition of “ionization gauge coefficient” given in ISO 3529-3:1981. This quantity was formerly also referred to as “gauge constant”. 3.2.2 ionization sensitivity S +quantity given by cc 0 e 0 I I SS I p p + = (2) where I eis the emission curre
33、nt; I cis the ion current, measured at pressure p; I c0is the ion current, measured at pressure p 0 ; p is the pressure; p 0is the residual pressure; S is the sensitivity (3.2.1). NOTE This definition cancels and replaces the definition of “sensitivity coefficient”, synonym “sensitivity”, given in I
34、SO 3529-3:1981. ISO 27894:2009(E) ISO 2009 All rights reserved 53.2.3 relative sensitivity factor r xquantity given by 2 x x N S r S = (3) where S xis the sensitivity for a specified gas species “x”; S N 2is the sensitivity for nitrogen for the same gauge at the same pressure and the same operating
35、conditions. NOTE 1 Adapted from ISO 3529-3:1981. NOTE 2 The pressure reading p indof a gauge which is correct for nitrogen has to be divided by the relative sensitivity factor r xof a gas species to obtain the correct pressure p xof the gas, when it is measuring that gas. ind x x p p r = (4) 3.2.4 c
36、orrection factor f cfactor by which a pressure reading of a gauge has to be multiplied to obtain the correct pressure according to a calibration ci n d p fp = (5) NOTE In a calibration, f cis determined by the quotient of the pressure standard p stdand the indicated reading p UUCof the unit under ca
37、libration; f cmay depend on pressure. std c UUC p f p = (6) 3.2.5 relative correction factor f c x/N 2quantity given by 2 2 cx cx/N cN f f f = (7) where f c xis the correction factor for a specified gas species “x”; f c N 2is the correction factor for nitrogen for the same gauge at the same pressure
38、 and the same operating conditions. NOTE 1 The pressure reading p indof a gauge which is correct for nitrogen has to be multiplied by the relative correction factor of a gas species to obtain the correct pressure of the gas, when it is measuring that gas. 2 c x /N ind pf p = (8) NOTE 2 f c x/N 2may
39、depend on the pressure. ISO 27894:2009(E) 6 ISO 2009 All rights reserved3.2.6 warm-up time time after which the ion gauge reading is stable within a specified value (e.g. 2 %) at a constant pressure after switching on the gauge NOTE There should be no trend in the gauge reading at constant pressure
40、after warm-up time. 3.2.7 residual current smallest ion collector current that can be obtained when the gauge is operated at its normal operating conditions and at a pressure that is zero or negligible compared with the lower measurement pressure limit of the gauge NOTE The residual current can be m
41、easured in a baked-out ultra-high vacuum system with the ionization gauge in the baked-out and degassed condition. The residual pressure is defined as the ion current obtained when the vacuum system has returned to normal room temperature 30 C, 48 h after stopping bake-out. The residual current is m
42、ainly composed of the X-ray effect, the inverse X-ray effect, the electron-stimulated desorption effect, outgassing and leakage currents from other potentials. 3.2.8 residual current-equivalent pressure equivalent pressure of nitrogen to the residual current (3.2.7) NOTE The residual current-equival
43、ent pressure is given in pascals (Pa). 3.2.9 internal volume vacuum gauges volume inside the envelope up to the sealing plane minus the volume of the electrodes reaching out of the sealing plane NOTE The internal volume is the volume of the gauge tube exposed to a vacuum system. For a nude gauge, in
44、 extreme cases, the internal volume may be negative, when the electrode volumes exceed the volume below the sealing plane. 4 Symbols and abbreviated terms Symbol Designation Unit f ccorrection factor 1 p pressure Pa p 0residual pressure Pa p indindicated pressure of a gauge Pa p stdpressure of a pri
45、mary or reference standard Pa p UUCindicated pressure of a unit (gauge) under calibration Pa r xrelative sensitivity factor 1 I eemission current A I cion current at pressure p A I c0ion current at pressure p 0A S sensitivity (coefficient) Pa 1S +ionization sensitivity APa 1ISO 27894:2009(E) ISO 200
46、9 All rights reserved 75 Principle of hot cathode ionization gauge Electrons emitted from the cathode are accelerated by the anode (grid) potential to ionize gas molecules that are within their way, which then produce an ion current collected by the ion collector. The ion current I cis proportional
47、to the gas density, or pressure p at constant temperature T; I cis given by ce p I Il kT = (9) where I eis the emission current; is the ionization cross-section area; l is the mean path length of the electron; k is the Boltzmann constant. There may be additional electrodes for different purposes. Th
48、e number of electrodes, their configuration and their shape depend on the specific type of hot cathode ionization gauge. 6 Specifications for hot cathode ionization gauge to be provided by manufacturers The features and specifications given in 6.1 to 6.20 shall be provided by the manufacturer, in or
49、der to enable users of their gauges to estimate the measurement uncertainty and/or to disseminate the pressure scale. 6.1 Type of gauge The manufacturer shall specify the gauge type, such as triode gauge, Bayard-Alpert gauge, extractor gauge, to mention just a few common types. For combined gauges, all types of gauges including the non-ionization gauge type shall be specified. 6.2 Display and measurement signal output The display of the gauge shall show the SI unit of pascal (Pa). Other un
