1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 27893:2011Vacuum technology Vacuumgauges Evaluation ofthe uncertainties of resultsof calibrations by directcomparison with a referencegaugeBS ISO 27893:2011 BRITISH STANDA
2、RDNational forewordThis British Standard is the UK implementation of ISO 27893:2011.The UK participation in its preparation was entrusted to TechnicalCommittee MCE/8/-/4, Vacuum technology.A list of organizations represented on this committee can beobtained on request to its secretary.This publicati
3、on does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 74391 7ICS 23.160Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority
4、of theStandards Policy and Strategy Committee on 31 August 2011.Amendments issued since publicationDate Text affectedBS ISO 27893:2011Reference numberISO 27893:2011(E)ISO 2011INTERNATIONAL STANDARD ISO27893First edition2011-08-15Vacuum technology Vacuum gauges Evaluation of the uncertainties of resu
5、lts of calibrations by direct comparison with a reference gauge Technique du vide Manomtres vide valuation de lincertitude des rsultats des talonnages par comparaison directe avec un manomtre de rfrence BS ISO 27893:2011ISO 27893:2011(E) COPYRIGHT PROTECTED DOCUMENT ISO 2011 All rights reserved. Unl
6、ess 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 member body in the country of the requester. ISO
7、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 2011 All rights reservedBS ISO 27893:2011ISO 27893:2011(E) ISO 2011 All rights reserved iiiContents Page Foreword iv 1 Scope 1 2 Nor
8、mative references 1 3 Terms and definitions . 2 4 Symbols and abbreviated terms 3 5 Basic concept and model . 3 5.1 General . 3 5.2 Sum model . 4 5.3 Quotient model 4 5.4 Combination of the two models . 5 6 Calculation of uncertainty in the sum model . 5 6.1 Total uncertainty Sum model 5 6.2 Uncerta
9、inty contributions due to reference standard . 6 6.3 Uncertainty contributions due to unit under calibration . 7 6.4 Uncertainty contributions due to calibration method or calibration conditions 8 6.5 Coverage factor . 8 7 Calculation of uncertainty in the quotient model . 9 7.1 Total uncertainty Qu
10、otient model . 9 7.2 Uncertainty contributions due to reference standard . 9 7.3 Uncertainty contributions due to the unit under calibration 10 7.4 Uncertainty contributions due to calibration method or calibration conditions 11 7.5 Coverage factor . 12 8 Combination of the sum and quotient model fo
11、r error of reading . 13 9 Reporting uncertainties 13 9.1 Uncertainty budget 13 9.2 Calibration certificate 14 Bibliography 15 BS ISO 27893:2011ISO 27893:2011(E) iv ISO 2011 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national stan
12、dards bodies (ISO member bodies). The work of preparing International 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 org
13、anizations, governmental and non-governmental, in liaison with 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
14、 in the ISO/IEC Directives, Part 2. The main task of technical 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
15、 % of the member bodies casting a vote. Attention is drawn to 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 27893 was prepared by Technical Committee ISO/TC 112, Vac
16、uum technology. This first edition of ISO 27893 cancels and replaces the first edition of ISO/TS 27893:2009, which has been technically revised. BS ISO 27893:2011INTERNATIONAL STANDARD ISO 27893:2011(E) ISO 2011 All rights reserved 1Vacuum technology Vacuum gauges Evaluation of the uncertainties of
17、results of calibrations by direct comparison with a reference gauge 1 Scope This International Standard gives guidelines for the determination and reporting of measurement uncertainties arising during vacuum gauge calibration by direct comparison with a reference gauge carried out in accordance with
18、 ISO/TS 3567. This International Standard describes methods for uniform reporting of uncertainties in vacuum gauge certificates. Uncertainties reported in accordance with the guidelines given in this International Standard are transferable in the sense that the uncertainty evaluated for one result c
19、an be used as a component in the uncertainty evaluation of another measurement or calibration in which the first result is used. This International Standard defines two measurement models that are sufficient to cover most practical cases. However, it is possible that the models given cannot be appli
20、ed to newly developed vacuum gauges. The final uncertainty to be reported in a certificate is evaluated from the uncertainties of the input quantities and influence quantities. The principal quantities that can affect the result of a vacuum calibration are described; however, a complete list of the
21、possible quantities that can have an influence on the final result lies outside the scope of this International Standard. NOTE It is envisaged that future Technical Specifications will address the calibration of specific types of vacuum gauges. 2 Normative references The following referenced documen
22、ts 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/TS 3567, Vacuum gauges Calibration by direct comparison with a reference gaug
23、e ISO/IEC Guide 98-3, Uncertainty of measurement Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) ISO/IEC Guide 99:2007, International vocabulary of metrology Basic and general concepts and associated terms (VIM) BS ISO 27893:2011ISO 27893:2011(E) 2 ISO 2011 All rights reserv
24、ed3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO/TS 3567, ISO/IEC Guide 98-3, ISO/IEC Guide 99 and the following apply. 3.1 corrected reading value resulting after the reading of the gauge has been corrected for systematic errors EXAMPLE For the res
25、ults given in the calibration certificate of the reference standard. 3.2 long-term instability possible change of calibrated value after long periods of time EXAMPLE Change resulting from transportation of the device. NOTE Long-term instability is different from reproducibility as defined in ISO/IEC
26、 Guide 99:2007, 3.7. 3.3 model uncertainty of measurementmathematical model set out in ISO/IEC Guide 98-3 3.4 offset measuring instruments zero error datum measurement error where the specified measured quantity value is zero NOTE Adapted from ISO/IEC Guide 99:2007, 4.28. EXAMPLE The reading when th
27、ere is no pressure (absolute or differential) or a pressure far below the resolution limit applied to a vacuum gauge. 3.5 deviation of offset Possible difference of an offset (3.4) value between the time of the measurement of the offset (3.4) and the time when a pressure reading is taken 3.6 referen
28、ce standard reference gauge standard, generally having the highest metrological quality available at a given location or in a given organization, from which measurements made there are derived NOTE Adapted from ISO/IEC Guide 99:2007, 6.6. EXAMPLE The gauge or standard that gives traceability to the
29、SI unit in the calibration apparatus in accordance with ISO/TS 3567. 3.7 calibration pressure vacuum gauges pressure evaluated from the corrected reading (3.1) of the reference standard (3.6) and all necessary corrections at the gauge port of the unit under calibration EXAMPLE Necessary corrections
30、might be for known differences between gauge ports. BS ISO 27893:2011ISO 27893:2011(E) ISO 2011 All rights reserved 34 Symbols and abbreviated terms Symbol or abbreviated term Designation Unit UUC unit under calibration (vacuum gauge) e error of reading in relative units k coverage factor to expand
31、standard uncertainty, u 1 pUUCpressure indication of a UUC corrected for known deviations Pa1)pind,UUCpressure indication of a UUC not corrected for any deviation Pa pstdpressure indication of reference gauge (reference standard) corrected for known deviations Pa pind,stdpressure indication of refer
32、ence gauge (reference standard) not corrected for any deviation Pa rUUC quantity determined by a calibration in the quotient model any unit rstdthe quantity that was determined for the reference standard any unit S sensitivity of the output of a vacuum gauge any unit u standard uncertainty any unit
33、U expanded uncertainty any unit xUUCindication of a UUC any unit xstdindication of a reference gauge any unit xi(often unknown) input quantities and corrections of gauge any unit Xi(often unknown) input quantities and corrections of calibration method or condition any unit p error of reading in abso
34、lute units Pa pideviations in the pressure unit (often unknown) Pa xi(often unknown) deviations in the x any unit effeffective accommodation coefficient of a spinning rotor gauge 1 5 Basic concept and model 5.1 General In a vacuum gauge calibration carried out in accordance with ISO/TS 3567, the cor
35、rected reading of a reference gauge gives the value of the quantity that is traceable to the SI. All vacuum gauges shall be calibrated in terms of pressure. This means that the user of the vacuum gauge calibrated in accordance with ISO/TS 3567 and this International Standard obtains a clear assignme
36、nt of the output quantity of the gauge to the SI unit of pressure, the pascal. 1) 1 Pa = 0,01 mbar. BS ISO 27893:2011ISO 27893:2011(E) 4 ISO 2011 All rights reservedThe value of pressure obtained from the corrected reading of the reference standard output can be used to determine the pressure at the
37、 entrance port of the unit under calibration (UUC). This is referred to as calibration pressure value. Often the corrected reading of the reference standard is identical to the calibration pressure value and valid for all gauge ports. The calibration pressure value can be used to determine an error
38、of the reading, p, of the unit under calibration. In this case, a sum model gives an adequate description of the measurement. The calibration pressure value can also be used to determine a correction factor, a sensitivity coefficient, an effective accommodation coefficient or a gauge constant, in wh
39、ich case a quotient model gives an adequate description of the measurement. In both models it can be assumed that all the input quantities are uncorrelated. 5.2 Sum model In the sum model, the difference between the reading of the UUC, pind, and the “true” calibration pressure traceable to the SI un
40、its is taken as the measurand, p. The calibration pressure is given by the reference standard pressure value, pstd, and possibly by a correction term, pm, due to the calibration method considering known effects like height correction, thermal transpiration, and pressure non-uniformity. The general s
41、um model thus becomes UUC std mpp p p (1) The first term refers to the UUC, the second to the reference standard, and the third to the calibration method. The sum of the last two terms gives the calibration pressure value. All quantities shall be expressed in the SI unit of pressure, the pascal. Eac
42、h of these terms is again expressed by another model equation, which makes all necessary corrections due to offsets, temperature corrections, deviation of indication from the SI value in accordance with the calibration certificate, etc. 5.3 Quotient model In the quotient model, the ratio of the read
43、ing of the UUC, xUUC, and the standard pressure value, pstd, is taken as the measurand, rUUC. The general quotient model thus becomes UUCUUCstdiixrXp(2) The numerator refers to the UUC, the denominator to the reference standard, and the product to the calibration method and conditions. The latter ca
44、n also be defined by the vacuum gauges under study, e.g. the emission current in a hot cathode ionization gauge. It is possible to express xindin any reasonable unit, e.g. that of pressure, voltage or current. The Xican be expressed in any meaningful physical unit or can be without dimension. Each o
45、f these factors is expressed by another model equation, which makes all necessary corrections due to offsets, temperature corrections, deviation of indication in accordance with calibration certificate, etc. Examples of rUUCare a) 1cfthe reciprocal of a dimensionless correction factor, where xUUC pU
46、UCand Xi 1; b) S a sensitivity of the analogue output, VUUC, of a capacitance diaphragm gauge, where xUUC VUUC; c) S a sensitivity of the analogue output, VUUC, of a thermal conductivity gauge, where xUUC VUUC; BS ISO 27893:2011ISO 27893:2011(E) ISO 2011 All rights reserved 5d) effthe effective acco
47、mmodation coefficient of a spinning rotor gauge, where xUUC pUUC, when eff 1 was entered into the controller; e) S a sensitivity of a Bayard-Alpert gauge with a hot cathode, where xUUC IUUCis the positive ion current of the collector and X1 1/Ie, where Ieis the emission current. 5.4 Combination of t
48、he two models It is possible to evaluate some of the input quantities in each model by either of the two models. First, for example, pstdas well as its uncertainty can be evaluated by the quotient model, thus stdstdstdxpr (3) The result can then be used in Equation (1). This is unavoidable if rstdis
49、 given in the certificate applying Equation (2) (e.g. the sensitivity of an analogue output), where rUUCis replaced by rstd. It is, however, not recommended to combine the sum and quotient model in one equation. This task should be left to experts, since complicated sensitivity coefficients might appear that are not covered in this International Standard for reasons of clarity. The relative error of reading, e, however, is a common case, where an easy to handle combination of the
