ASTM_D_7720_-_21.pdf

Designation:D772021Standard Guide forStatistically Evaluating Measurand Alarm Limits when UsingOil Analysis to Monitor Equipment and Oil for Fitness andContamination1This standard is issued under the fixed designation D7720;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.Scope*1.1 This guide provides specific requirements to statisticallyevaluate measurand alarm thresholds,which are called alarmlimits,as they are applied to data collected from in-service oilanalysis.These alarm limits are typically used for conditionmonitoring to produce severity indications relating to states ofmachinery wear,oil quality,and system contamination.Alarmlimits distinguish or separate various levels of alarm.Fourlevels are common and will be used in this guide,though threelevels or five levels can also be used.1.2 A basic statistical process control technique describedherein is recommended to evaluate alarm limits when mea-surand data sets may be characterized as both parametric and incontrol.A frequency distribution for this kind of parametricdata set fits a well-behaved two-tail normal distribution havinga“bell”curve appearance.Statistical control limits are calcu-lated using this technique.These control limits distinguish,at achosen level of confidence,signal-to-noise ratio for an in-control data set from variation that has significant,assignablecauses.The operator can use them to objectively create,evaluate,and adjust alarm limits.1.3 A statistical cumulative distribution technique describedherein is also recommended to create,evaluate,and adjustalarm limits.This particular technique employs a percentcumulative distribution of sorted data set values.The techniqueis based on an actual data set distribution and therefore is notdependent on a presumed statistical profile.The technique maybeusedwhenthedatasetiseitherparametricornonparametric,and it may be used if a frequency distributionappears skewed or has only a single tail.Also,this techniquemay be used when the data set includes special cause variationin addition to common cause variation,although the techniqueshould be repeated when a special cause changes significantlyor is eliminated.Outputs of this technique are specific mea-surand values corresponding to selected percentage levels in acumulative distribution plot of the sorted data set.Thesepercent-based measurand values are used to create,evaluateand adjust alarm limits.1.4 This guide may be applied to sample data from testingof in-service lubricating oil samples collected from machinery(for example,diesel,pumps,gas turbines,industrial turbines,hydraulics)whether from large fleets or individual industrialapplications.1.5 This guide may also be applied to sample data fromtesting in-service oil samples collected from other equipmentapplications where monitoring for wear,oil condition,orsystem contamination are important.For example,it may beapplied to data sets from oil filled transformer and circuitbreaker applications.1.6 Alarm limit evaluating techniques,which are not statis-tically based are not covered by this guide.Also,the techniquesof this standard may be inconsistent with the following alarmlimitselectiontechniques:“rate-of-change,”absolutealarming,multi-parameter alarming,and empirically derivedalarm limits.1.7 The techniques in this guide deliver outputs that may becompared with other alarm limit selection techniques.Thetechniques in this guide do not preclude or supersede limits thathave been established and validated by an Original EquipmentManufacturer(OEM)or another responsible party.1.8 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,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.9 This international standard was developed in accor-dance with internationally 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.1This guide is under the jurisdiction of ASTM Committee D02 on PetroleumProducts,Liquid Fuels,and Lubricants and is the direct responsibility of Subcom-mittee D02.96.04 on Guidelines for In-Services Lubricants Analysis.Current edition approved Oct.1,2021.Published October 2021.Originallyapproved in 2011.Last previous edition approved in 2017 as D7720 11(2017).DOI:10.1520/D7720-21.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard