1、Designation: E2554 13 An American National StandardStandard Practice forEstimating and Monitoring the Uncertainty of Test Resultsof a Test Method Using Control Chart Techniques1This standard is issued under the fixed designation E2554; the number immediately following the designation indicates the y
2、ear oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes techniques for a laboratory t
3、oestimate the uncertainty of a test result using data from testresults on a control sample. This standard provides one methodfor a laboratory to estimate Measurement Uncertainty inaccordance with Section A22.3 in Form and Style of ASTMStandards.1.2 Uncertainty as defined by this practice applies to
4、thecapabilities of a single laboratory. Any estimate of uncertaintydetermined through the use of this practice applies only to theindividual laboratory for which the data are presented.1.3 The laboratory uses a well defined and established testmethod in determining a series of test results. The unce
5、rtaintyestimated using this practice only applies when the same testmethod is followed. The uncertainty only applies for thematerial types represented by the control samples, and multiplecontrol samples may be needed, especially if the method hasdifferent precision for different sample types or resp
6、onse levels.1.4 The uncertainty estimate determined by this practicerepresents the intermediate precision of test results. Thisestimate seeks to quantify the total variation expected within asingle laboratory using a single established test method whileincorporating as many known sources of variatio
7、n as possible.1.5 This practice does not establish error estimates (errorbudget) attributed to individual factors that could influenceuncertainty.1.6 This practice describes the use of control charts toevaluate the data obtained and presents a special type of controlchart to monitor the estimate of
8、uncertainty.1.7 The system of units for this standard is not specified.Dimensional quantities in the standard are presented only asillustrations of calculation methods. The examples are notbinding on products or test methods treated.1.8 This standard does not purport to address all of thesafety conc
9、erns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.9 This international standard was developed in accor-dance with internationally
10、recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D5184 Test Metho
11、ds for Determination of Aluminum andSilicon in Fuel Oils by Ashing, Fusion, InductivelyCoupled Plasma Atomic Emission Spectrometry, andAtomic Absorption SpectrometryE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE456 Terminology Relating to Quality and StatisticsE2282 Guide
12、 for Defining the Test Result of a Test MethodE2587 Practice for Use of Control Charts in StatisticalProcess ControlISO/ASTM 51707 Guide for Estimating Uncertainties inDosimetry for Radiation Processing2.2 ASTM Publications:2Form and Style for ASTM StandardsManual on Presentation of Data and Control
13、 Chart Analy-sis 7th Edition2.3 ISO Standard:3ISO/IEC 17025 General Requirements for the Competenceof Testing and Calibration Laboratories3. Terminology3.1 DefinitionsThe terminology of Terminology E456applies to this practice except as modified herein.1This practice is under the jurisdiction of AST
14、M Committee E11 on Quality andStatistics and is the direct responsibility of Subcommittee E11.20 on Test MethodEvaluation and Quality Control.Current edition approved April 1, 2013. Published May 2013. Originallyapproved in 2007. Last previous edition approved in 2007 as E2554 07. DOI:10.1520/E2554-
15、13.2For 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 website.3Available from American National Standards Institute (ANS
16、I), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization
17、established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.1 control sample, nsample taken from a stable, homo-geneous material for the purposes of monitor
18、ing the perfor-mance of a test method in a laboratory.3.1.1.1 DiscussionThe control sample material is repre-sentative of the product typically tested in the laboratory by thegiven test method. A control sample is run periodically usingthe complete test method protocol to develop a test result. Such
19、test results may be statistically evaluated to monitor testmethod performance over time. It is not necessary to have anaccepted reference value assigned to the control sample mate-rial. When the current material is nearly consumed, a replace-ment material should be run in parallel with the currentma
20、terial to ensure continuity in the control sample program.3.1.2 check sample, nsee control sample.3.1.3 intermediate precision, nthe closeness of agreementbetween test results obtained under specified intermediateprecision conditions. E1773.1.3.1 DiscussionThe specific measure and the specificcondit
21、ions must be specified for each intermediate measure ofprecision; thus, “standard deviation of test results amongoperators in a laboratory,” or “day-to-day standard deviationwithin a laboratory for the same operator.”3.1.3.2 DiscussionBecause the training of operators, theagreement of different piec
22、es of equipment in the samelaboratory and the variation of environmental conditions withlonger time intervals all depend on the degree of within-laboratory control, the intermediate measures of precision arelikely to vary appreciably from laboratory to laboratory. Thus,intermediate precisions may be
23、 more characteristic of indi-vidual laboratories than of the test method.3.1.4 test result, nthe value of a characteristic obtained bycarrying out a specified test method. E22823.1.5 repeatability, nprecision under repeatabilityconditions. E1773.2 Definitions of Terms Specific to This Standard:3.2.1
24、 uncertainty control chart, ncontrol chart that in-cludes control limits based on the variation attributed to theuncertainty of the test method.4. Significance and Use4.1 This practice provides one way for a laboratory todevelop data-based Type A estimates of uncertainty as referredto in Section A22
25、 in Form and Style of ASTM Standards.4.2 Laboratories accredited under ISO/IEC 17025 are re-quired to present uncertainty estimates for their test results.This practice provides procedures that use test results todevelop uncertainty estimates for an individual laboratory.4.3 Generally, these test re
26、sults will be from a single sampleof stable and homogeneous material known as a control orcheck sample.4.4 The true value of the characteristic(s) of the controlsample being measured will ordinarily be unknown. However,this methodology may also be used if the control sample is areference material, i
27、n which case the test method bias may alsobe estimated and incorporated into the uncertainty estimate.Many test methods do not have true reference materialsavailable to provide traceable chains of uncertainty estimation.4.5 This practice also allows for ongoing monitoring of thelaboratory uncertaint
28、y. As estimates of the level of uncertaintychange, possibly as contributions to uncertainty are identifiedand minimized, revision to the laboratory uncertainty will bepossible.5. General Considerations5.1 Materials to be Used:5.1.1 This methodology requires a quantity of stable andhomogeneous materi
29、al which will serve as the source ofcontrol samples (sometimes called check samples). The mate-rial shall be similar in composition to the samples of materialroutinely analyzed by this test method in this laboratory. Bystable it is assumed that the test results obtained from thismaterial should be c
30、onsistent over the time interval that thismaterial will be used. By homogeneous it is assumed thatsamples taken from the material source will not have asignificant variation in the characteristic measured by the testmethod.5.1.2 For destructive testing of control sample materials,provision shall be
31、made for depletion and replacement of thecontrol sample material.5.1.2.1 In some cases, the test method may be nondestruc-tive and the same material may be reused indefinitely.5.1.2.2 In other cases, the material may be used up,deteriorate, or otherwise gradually change.5.1.3 The test method should
32、describe the best practices forpreparing and storing the control material and taking thecontrol samples.5.2 Test Conditions:5.2.1 An uncertainty estimation program should be de-signed to include all known sources of variation, such asoperators (analysts), equipment, reagents, and so forth, andthese
33、should be deliberately incorporated into the design of theprogram. In general, these sources of variation will be defined(including acceptable tolerances) by the test method.5.2.2 In cases in which control over such variations is notpossible or undefined, at least 30 to 50 sampling periods shallbe e
34、valuated to permit environmental and other factors to beincorporated in the overall estimate.6. Overall ProcedureControl Charting Methods6.1 General concepts of control charts are described else-where. For more information, see Practice E2587 as well asManual 7A.46.2 The general procedure involves t
35、wo major phases:Preliminary and Monitoring.6.2.1 Preliminary Phase:6.2.1.1 This phase begins with an initial collection of testresults.6.2.1.2 Preliminary control charts are then prepared andexamined. These charts are evaluated to determine if the4Manual on Presentation of Data and Control Chart Ana
36、lysis: 7th Edition,ASTM International, West Conshohocken, PA, 2001.E2554 132process is in a state of statistical control. The usual principlesof control charting utilize short-term variability to estimate thelimits within which samples of test results should vary. Forcontrol sample programs this sho
37、rt-term variability is equiva-lent to repeatability precision. It is expected, however, thatadditional contributions to variation will be present over timeand therefore additional variation, equivalent to intermediateprecision, will be encountered.6.2.1.3 An estimate of uncertainty standard deviatio
38、n isdeveloped.6.2.1.4 An uncertainty control chart is then prepared tomonitor future sample results.6.2.2 Monitoring Phase:6.2.2.1 The proposed uncertainty control chart is used toprovide evidence that the estimate of uncertainty is notexceeding the estimated value.6.2.2.2 The estimate of uncertaint
39、y should be periodicallyre-evaluated.6.2.2.3 Where appropriate, it is recommended that a stan-dard control chart also be maintained to determine whether thevariation over time has been reduced to the level of short-termvariation (repeatability).6.3 Two types of control charting methods are recom-men
40、ded to develop estimates of uncertainty. These include:6.3.1 Mean (Xbar) and range or standard deviation chartsare used when multiple test results are conducted in each timeperiod.6.3.2 Individual charts (IndX) are used when single testresults are obtained in each time period.6.4 Variation Estimates
41、:6.4.1 Either a range chart or a standard deviation chart maybe used to estimate the short-term variability when multipleassays are conducted under repeatability conditions per timeperiod. An estimate from the control chart data can becompared to other estimates of repeatability (within laboratory,s
42、hort-term variation) if available.6.4.2 Sample averages are examined and may provideestimates of variation caused by other factors. Such factorsmay include environmental effects, operator factors, reagents,or instruments.6.5 Systematic Procedures:6.5.1 Specifically designed experiments can be used t
43、oensure all known sources of variation, such as operators(analysts), equipment, reagents, or instruments are incorpo-rated in the general study.6.5.2 The data generated from this program is available foradditional uses, such as control charting to evaluate trends,stratification by analysis, or strat
44、ification by equipment toidentify training or maintenance needs or both.7. Specific Procedures7.1 Multiple Test Results Generated Per Time Period:7.1.1 A specified number of independent test results aretaken during each time period. Generally this number is 5 orless. It is preferred that at least 25
45、 sets of test results beobtained before developing the charts.7.1.2 Either a range chart or a standard deviation chart isprepared. This is examined for special cause variation. If thevariability appears random then an estimate of repeatability iscomputed. This may be done by pooling the sums of squa
46、res,using the average standard deviation, or using the averagerange.NOTE 1If the ranges or standard deviations are zero in most of thesamples, then this estimate of repeatability standard deviation is suspectand probably unusable. This is usually the result of insufficient resolutionof the measureme
47、nt system in use or severe rounding. An estimate basedon the minimum interval size should be substituted for the zeros.As a ruleof thumb, consider replacing the zeros when more than about13 are zeros.7.1.3 A means chart is used to examine variation amongtime periods. Limits on this chart permit comp
48、arison ofvariation between time periods using repeatability as theestimate of error.7.1.3.1 If the control chart shows a state of statistical controlthen the uncertainty will be assumed approximately equivalentto the repeatability standard deviation.7.1.3.2 In most cases it will be expected that the
49、 variabilitybetween means will show an “out of control” conditionindicating that there are “special” causes of variation inaddition to repeatability. The between means variation andwithin means repeatability estimates are then used to computean estimate of uncertainty standard deviation.7.1.4 Using the estimate of uncertainty standard deviationan Uncertainty Control Chart is prepared for future monitoringof the uncertainty. This chart may include control limits formeans as a possible lower set of control limits along with theuncertainty control limits based on the esti
