1、 Intentionally left blank AN AMERICAN NATIONAL STANDARDGUIDELINES FOR DECISION RULES:CONSIDERING MEASUREMENTUNCERTAINTY IN DETERMININGCONFORMANCE TO SPECIFICATIONSASME B89.7.3.1-2001Date of Issuance: March 18, 2002This Standard will be revised when the Society approves the issuance of anew edition.
2、There will be no addenda issued to this edition.ASME will issue written replies to inquiries concerning interpretation oftechnical aspects of this Standard.ASME is the registered trademark of The American Society of Mechanical Engineers.This code or standard was developed under procedures accredited
3、 as meeting the criteria forAmerican National Standards. The Standards Committee that approved the code or standardwas balanced to assure that individuals from competent and concerned interests have had anopportunity to participate. The proposed code or standard was made available for public reviewa
4、nd comment that provides an opportunity for additional public input from industry, academia,regulatory agencies, and the public-at-large.ASME does not “approve,” “rate,” or “endorse” any item, construction, proprietary device,or activity.ASME does not take any position with respect to the validity o
5、f any patent rights asserted inconnection with any items mentioned in this document, and does not undertake to insure anyoneutilizing a standard against liability for infringement of any applicable letters patent, nor assumeany such liability. Users of a code or standard are expressly advised that d
6、etermination of thevalidity of any such patent rights, and the risk of infringement of such rights, is entirely theirown responsibility.Participation by federal agency representative(s) or person(s) affiliated with industry is not tobe interpreted as government or industry endorsement of this code o
7、r standard.ASME accepts responsibility for only those interpretations of this document issued inaccordance with the established ASME procedures and policies, which precludes the issuanceof interpretations by individuals.No part of this document may be reproduced in any form,in an electronic retrieva
8、l system or otherwise,without the prior written permission of the publisher.The American Society of Mechanical EngineersThree Park Avenue, New York, NY 10016-5990Copyright 2002 byTHE AMERICAN SOCIETY OF MECHANICAL ENGINEERSAll Rights ReservedPrinted in U.S.A.CONTENTSForeword ivCommittee Roster viCor
9、respondence With the B89 Committee . viiAbstract . viii1 Scope 12 Definitions . 13 Requirements for Decision Rules 23.1 2Zone Identification .3.2 2Decision Outcome .3.3 2Repeated Measurements 3.4 2Data Rejection 4 Acceptance and Rejection Zones in Decision Rules . 34.1 3Simple Acceptance and Rejecti
10、on Using a N:1 Decision Rule 4.2 4Stringent Acceptance and Relaxed Rejection Using a Z% Guard Band .4.3 4Stringent Rejection and Relaxed Acceptance Using a Z% Guard Band .4.4 5Decision Rules With a Transition Zone .5 Examples of Decision Rules 55.1 55.2 65.3 65.4 6Figures1 An Example of Guard Bands
11、Used for Creating a Binary Decision RuleWith Stringent Acceptance and Relaxed Rejection Zones 32 3An Example of Simple Acceptance and Rejection Using a 4:1 Ratio .3 4Stringent Acceptance and Relaxed Rejection Examples .4 5Symmetric Two-Sided Relaxed Acceptance and Stringent Rejection .5 Stringent Ac
12、ceptance, Simple Rejection, and a Transition Zone ExampleUsing Symmetric Two-Sided Guard Banding 5Nonmandatory AppendicesA 7Application of Decision Rules in the Customer-Supplier Relationship .B 8Repeated Measurement .C 9Outlier Measurement Results .D 10Special Issues of Decision Rules for Instrumen
13、tation E 12Determination of Guard Band Limits .F 13A Discussion of ISO 14253-1 G 14References iiiFOREWORDThe intent of these guidelines is to facilitate the development of understanding betweensuppliers and customers regarding measurement uncertainty in the decision to accept or toreject a product.
14、Metrologists are continuously faced with the task of making decisions inthe presence of measurement uncertainty. To formalize this task, procedures known asdecision rules have been developed. A decision rule is a prescription for the acceptanceor rejection of products based on the measurement result
15、 of a characteristic of the product,the permissible variation associated with that characteristic, and the uncertainty of themeasurement result. For workpieces, the permissible variation is commonly called thetolerance; for instruments it is often given by the specification limits or maximum permiss
16、ibleerror (MPE). The terminology of ISO 14253-1 has been adopted and the permitted variationof a products characteristic is referred to as the specification zone. This document isintended to provide guidance on decision rules and their implementation.A related document, ASME B89.7.2-1999, Dimensiona
17、l Measurement Planning, specifiesrequirements for preparation and approval of dimensional measurement plans and for theuse of approved plans in making dimensional measurements. The dimensional measurementplan must contain or reference all information for making measurements, including specificationo
18、f a decision rule. ASME B89.7.3.1 serves as a resource to the dimensional measurementplanner by providing terminology and specifying the requirements for decision rules foruse in dimensional measurement plans.The Guide to the Expression of Uncertainty in Measurement, (GUM), NCSL Z540-2-1997 provides
19、 a unified means of evaluating and expressing the uncertainty of a measurementresult; consequently the calculational details of evaluating the uncertainty of a measurementresult will not be discussed. Unless otherwise stated, the term “measurement uncertainty”will be used to mean the expanded uncert
20、ainty, U, with a coverage factor of two, whichis the most common coverage factor used nationally and internationally.Although all traceable measurement results include an uncertainty statement not allmeasurement results involve decision rules. (See ISO International Vocabulary of Basic andGeneral Te
21、rms in Metrology.) Many calibrations, particularly at National MeasurementInstitutes (NMIs), typically state a description of the measurement, its result, and itsuncertainty; decision rules are not involved since there are no specifications. Most products,however, have stated specifications and a de
22、cision must be reached regarding the productscharacteristic relative to its stated specifications.The decision rule in use should be well documented to prevent ambiguity in the acceptanceor rejection of product. The selection of a particular decision rule is ultimately a businessdecision; some of th
23、e factors to be considered are outlined in nonmandatory AppendicesA and D.The concept of a decision rule has a long history and over the years has developedmany variations including “gauge makers rule,”“test accuracy ratio (TAR),”“test uncertaintyratio (TUR),”“four-to-one rule,”“gauging ratio,”“guar
24、d bands,”“gauging limit,” and manymore. Most of these terms were defined before the development of the GUM and henceconcepts such as “accuracy” or “uncertainty” were nebulously defined. One of the motivationsof these guidelines is to explicitly define the decision rule concept and have some well-doc
25、umented decision rules that can be referenced. Consequently, these guidelines haveencapsulated some of the commonly used procedures and their specifically-named deci-sion rules.ivThe terminology used in these guidelines is consistent with national and internationalstandards whenever possible. Descri
26、ptors such as “stringent” and “relaxed,” used in describingconformance and nonconformance, have been carefully chosen. For example, stringentacceptance is meant to imply both a decrease in the acceptance zone width and an increasein confidence that a measurement result in this zone is associated wit
27、h an in-specificationproduct. Similarly, stringent rejection results in a decreased size of the rejection zone whileincreasing the confidence that a measurement result in this zone is associated with an out-of-specification product. The converse situation applies to relaxed acceptance and rejection.
28、The decision rules formulated using these guidelines ensure a self-consistent procedurefor an organization to accept or to reject products. The situation becomes more complicatedwhen two or more parties are involved, commonly a supplier and a customer, each ofwhich is using a different measurement s
29、ystem with a different uncertainty and possiblyusing a different decision rule (this topic is very briefly discussed in nonmandatory AppendixA). Such a situation has the potential for conflicting decisions by the different parties, andconflict resolution is outside the scope of this document. When u
30、sing decision rules inmulti-party commerce, it is prudent to anticipate the potential conflicts that can arise (whichdepend on the details of the decision rules and the measurement systems involved) andagree upon a conflict resolution procedure prior to performing measurements.Comments and suggestio
31、ns for improvement of this Standard are welcomed. They shouldbe addressed to: ASME, Three Park Avenue, New York, NY 10016-5990This Standard was approved by the American National Standards Institute on December11, 2001.vASME STANDARDS COMMITTEE B89Dimensional Metrology(The following is the roster of
32、the Committee at the time of approval of this Standard.)OFFICERSB. Parry, ChairD. Beutel Vice ChairM. Lo, SecretaryCOMMITTEE PERSONNELK. L. Blaedel, University of California/Livermore Lab, Livermore, CaliforniaJ. B. Bryan, Bryan Associates, Pleasanton, CaliforniaT. Carpenter, US Air Force Metrology
33、Labs, Newark, OhioT. Charlton, Jr., Brown and Sharpe Manufacturing Co., North Kingston, Rhode IslandG. A. Hetland, Hutchinson Technology, Inc., Hutchinson, MinnesotaR. J. Hocken, University of North Carolina, Charlotte, North CarolinaM. Liebers, Professional Instruments, Minneapolis, MinnesotaB. R.
34、Taylor, Renishaw PLC, Gloucestershire, EnglandR. C. Veale, NIST, Gaithersburg, MarylandSUBCOMMITTEE 7: MEASUREMENT UNCERTAINTYG. Hetland, Chair, Hutchinson Technology, Inc., Hutchinson, MinnesotaD. Swyt, Vice Chair, NIST, Gaithersburg, MarylandW. Beckwith, Brown e.g., “acceptance using the XX rule.”
35、10When claiming product rejection, it is important to state thedecision rule; e.g., “rejection using the XX rule.”11There may be more than one transition zone; each should beseparately labeled.GUIDELINES FOR DECISION RULESASME B89.7.3.1-2001guard band: the magnitude of the offset from thespecificati
36、on limit to the acceptance or rejection zoneboundary.12, 13, 14, 15, 16, 17simple acceptance: the situation when the acceptancezone equals and is identical to the specification zone.simple rejection: the situation when the rejection zoneconsists of all values of the characteristic outside thespecifi
37、cation zone.stringent acceptance: the situation when the accept-ance zone is reduced from the specification zone bya guard band(s). See Fig. 1.18, 19relaxed rejection: the situation when the rejectionzone is partially inside the specification zone by theamount of a guard band. See Fig. 1.18relaxed a
38、cceptance: the situation when the acceptancezone is increased beyond the specification zone by aguard band.2012The symbol g is deliberately used for the guard band, instead ofthe symbol U employed in ISO 14253-1 since U is reserved forthe expanded uncertainty which is associated with a measurementre
39、sult and hence it is confusing to attach U to a specificationlimit. The evaluation of U is a technical issue, while the evaluationof g is a business decision.13The guard band is usually expressed as a percentage of theexpanded uncertainty, i.e., a 100% guard band has the magnitudeof the expanded unc
40、ertainty U.14Two-sided guard banding occurs when a guard band is applied toboth the upper and lower specification limits. (In some exceptionalsituations the guard band applied within the specification zone,gIn, could be different at the upper specification limit and at thelower specification limit.
41、This would reflect a different risk assess-ment associated with an upper or lower out-of-specification condi-tion depending on whether the characteristic was larger or smallerthan allowed by the specification zone.) If both the upper andlower guard bands are the same size then this is called symmetr
42、ictwo-sided guard banding.15A guard band is sometimes distinguished as the upper or lowerguard band, associated with the upper or lower specification limit.Subscripts are sometimes attached to the guard band notation, g,to provide clarity, e.g., gUpand gLo. See Fig. 1.16The guard band, g, is always
43、a positive quantity; its location,e.g., inside or outside the specification zone, is determined bythe type of acceptance or rejection desired. See Section 4.17While these guidelines emphasize the use of guard bands, anequivalent methodology is to use gauging limits as in ASMEB89.7.2-1999.18Stringent
44、 acceptance and relaxed rejection occur together in abinary decision rule.19The stringent acceptance zone is analogous to the conformancezone described in ISO 14253-1.20Relaxed acceptance and stringent rejection occur together in abinary decision rule.2stringent rejection: the situation when the rej
45、ectionzone is increased beyond the specification zone by aguard band.20mean measurement result: results of repeated measure-ments are arithmetically averaged to yield a meanmeasurement result. The mean result is used to deter-mine acceptance or rejection.data rejection with cause: repeated measureme
46、nts mayindicate that one or more measurement results signifi-cantly deviate from the rest of the results of measure-ment. If the measurement procedure has a documentedpolicy for addressing measurement rejection then thispolicy takes precedence. Otherwise, measurement re-sults may only be rejected if
47、 a physical cause can beestablished. Examples of physical causes for measure-ment rejection include: improper instrument settings,loose or improperly fixtured components, known tran-sient events such as vibrations caused by doorsslamming.3 REQUIREMENTS FOR DECISION RULES3.1 Zone IdentificationA deci
48、sion rule must have a well-documented methodof determining the location of the acceptance, rejection,and any transition zones.3.2 Decision OutcomeEach zone of a decision rule must correspond to adocumented decision that will be implemented shouldthe result of measurement lie in that zone. While this
49、is automatic for the acceptance and rejection zonesby definition, any transition zones must have theircorresponding decision outcome documented.3.3 Repeated MeasurementsA decision rule must state the procedure for ad-dressing repeated measurements of the same characteris-tic on the same workpiece or instrument. See AppendixB for further discussion of this issue.3.4 Data RejectionA decision rule must state the procedure for allowingdata rejection with cause, that is, rejection of “outliers.”See Appendix C for fu
