ASTM_E_2587_-_15.pdf

Designation:E258715An American National StandardStandard Practice forUse of Control Charts in Statistical Process Control1This standard is issued under the fixed designation E2587;the number immediately following the designation indicates the year 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 provides guidance for the use of controlcharts in statistical process control programs,which improveprocess quality through reducing variation by identifying andeliminating the effect of special causes of variation.1.2 Control charts are used to continually monitor productor process characteristics to determine whether or not a processis in a state of statistical control.When this state is attained,theprocess characteristic will,at least approximately,vary withincertain limits at a given probability.1.3 This practice applies to variables data(characteristicsmeasured on a continuous numerical scale)and to attributesdata(characteristics measured as percentages,fractions,orcounts of occurrences in a defined interval of time or space).1.4 The system of units for this practice is not specified.Dimensional quantities in the practice are presented only asillustrations of calculation methods.The examples are notbinding on products or test methods treated.1.5 This standard does not purport to address all of thesafety concerns,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.2.Referenced Documents2.1 ASTM Standards:2E456 Terminology Relating to Quality and StatisticsE1994 Practice for Use of Process Oriented AOQL andLTPD Sampling PlansE2234 Practice for Sampling a Stream of Product by Attri-butes Indexed by AQLE2281 Practice for Process and Measurement CapabilityIndicesE2762 Practice for Sampling a Stream of Product by Vari-ables Indexed by AQL3.Terminology3.1 Definitions:3.1.1 See Terminology E456 for a more extensive listing ofstatistical terms.3.1.2 assignable cause,nfactor that contributes to varia-tion in a process or product output that is feasible to detect andidentify(see special cause).3.1.2.1 DiscussionMany factors will contribute tovariation,but it may not be feasible(economically or other-wise)to identify some of them.3.1.3 attributes data,nobserved values or test results thatindicate the presence or absence of specific characteristics orcounts of occurrences of events in time or space.3.1.4 average run length(ARL),nthe average number oftimes that a process will have been sampled and evaluatedbefore a shift in process level is signaled.3.1.4.1 DiscussionA long ARL is desirable for a processlocated at its specified level(so as to minimize calling forunneeded investigation or corrective action)and a shortARL isdesirable for a process shifted to some undesirable level(sothat corrective action will be called for promptly).ARL curvesare used to describe the relative quickness in detecting levelshifts of various control chart systems(see 5.1.4).The averagenumber of units that will have been produced before a shift inlevel is signaled may also be of interest from an economicstandpoint.3.1.5 c chart,ncontrol chart that monitors the count ofoccurrences of an event in a defined increment of time orspace.3.1.6 center line,nline on a control chart depicting theaverage level of the statistic being monitored.3.1.7 chance cause,nsource of inherent random variationin a process which is predictable within statistical limits(seecommon cause).3.1.7.1 DiscussionChance causes may be unidentifiable,or may have known origins that are not easily controllable orcost effective to eliminate.3.1.8 common cause,n(see chance cause).1This practice is under the jurisdiction ofASTM Committee E11 on Quality andStatistics and is the direct responsibility of Subcommittee E11.30 on StatisticalQuality Control.Current edition approved April 1,2015.Published April 2015.Originallyapproved in 2007.Last previous edition approved in 2014 as E2587 141.DOI:10.1520/E2587-15.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.9 control chart,nchart on which are plotted a statis-tical measure of a subgroup versus time of sampling along withlimits based on the statistical distribution of that measure so asto indicate how much common,or chance,cause variation isinherent in the process or product.3.1.10 control chart factor,na tabulated constant,depend-ing on sample size,used to convert specified statistics orparameters