E XP

ENDITURES

EXPENDI TUR

ES

MeasurementUncertainty

MeasuredValue

ActualValue

NominalLowerspec.limit

Upperspec.limit

ASME B89.7Measurement Uncertainty

Understanding and Economic Benefits

Standards and Guidelines

Everything is viewed through the filter of measurement uncertainty.

Cp (process) = 1.33

0.0 0.1

0.2

0.0

0.4

0.6

0.8

1.0

1.6

1.4

1.2

1.8

2.0

0.3 0.4 0.5 0.6 0.7 0.8

Uncertainty/Tolerance

0.9 1.0

Cp (process) = 1.50

Cp (process) = 1.67

Cp (process) = 2.00

oa

1.27 U: UncertaintyT: Tolerance

10% GR &R

What is MeasurementUncertainty?

You’ve undertaken a measurement for a product designthat has been manufactured, assembled and inspected byyour supply chain.

� But what if your particular measurement might be“off” from what you would consider to be acceptable?

� How do you assess your likelihood of being “off”?

� How do you determine what is the acceptable rangefor being “off”?

� And how do you express this likelihood and range inquantitative terms – so that all parties in your supplychain can agree?

Clearly, the implications of such measurements areenormously significant throughout the manufacturing,assembling and inspection process, especially in such“big ticket” industries as medical, aerospace, automotive,disc-drive and energy. The potential impact on costscould range into millions of dollars. So it benefits allengineers greatly to be accurate in how they undertake,evaluate and communicate their measurements.

Image at lower right courtesy of “Productive Metrology, AddingValue to Manufacture,” by H. Kunzmann, T. Pfeifer, R. Schmitt,H. Schwenke, A. Weckenmann, published in the CIRP Annualvol. 54-2, 2005.

Measurement uncertainty is the quantitative evaluation ofthe reasonable values that are associated with a measure-ment result. It is a probabilistic expression of the doubtin a particular measurement value.

Whether addressing the performance tests of instrumentsor the calibrations of artifacts, ASME B89.7 documentsprovide the framework for assessing the measurementprocesses and quantifying the validity of the results ofmeasurement results. Results of measurements are thenumerical values produced by a measurement process.

Measurement uncertainty is a number that characterizesthe distribution of values that could reasonably be attrib-uted to the realization of the measurand, or particularquantity subject to measurement. As such, measurementuncertainty is an indicator of the quality and reliability ofmeasurement results and can be used as an effective toolto improve measurement processes.

The ASME B89 Division 7 committee was established with theintent of developing standards in the field of measurement un-certainty and to remain abreast of the latest developments inthe field. It also provides guidance to other B89 divisions. It isnoteworthy that documents created under the auspices of B89Division 7 are significantly broader in scope than traditionalB89 performance-testing standards as they include all ramifica-tions of and variations in the measuring process. It is alsoimportant to state the B89.7 Series of documents use Type Aand Type B evaluations and are 100% GUM (Guide to theExpression of Uncertainty in Measurement) compliant.

ASME B89 Division 7

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Measured results must be repeatable and reproduciblebut by itself can be both a technical and financial risk. Influence of measurement uncertainty on process parameters,

Design

MeasurementMfg

GD&T&

Uncertainty

Design

MeasurementMfg

GD&T&

Uncertainty

Measurement

Design

Mfg.

What Practitioners Say AboutMeasurement Uncertainty

The main goal for [measurement] uncertainty is to makesure the measurements taken by a certain system (gage,CMM or the like) are appropriate for the application. Thecost of having poor measurements is multiplied asthe nonconforming components move through theprocesses towards final assembly and on to acustomer.

—Paulo H. Pereira, Ph.D., ASQ-CQEGlobal QualityProduction Center of ExcellenceCaterpillar Inc.

Companies can save money with measurement uncer-tainty by being in a position to make better technical andbusiness decisions.

Companies using gage repeatability and reproducibility(GR&R) as their basis for measurement systems analysiswould be at high-risk. This limited method of analysis isnot capable of capturing the full magnitude of measure-ment error and biases induced by many influencing fac-tors. Measured results must be repeatable andreproducible, but by itself can be both a technicaland financial risk. It is easy to have measured re-sults that are repeatably and reproducibly incorrect,as uncorrected biases are easily induced that can bemany times larger than the GR&R numbers initially recog-nized by the metrologist.

Customers and suppliers already know when this is occur-ring, as one of the two following situations happens:Measurement data can look good -- it complies with speci-fication requirements, but the parts do not work or prop-erly fit. Or measurement data can look bad -- it does notcomply with specification requirements, but the parts ac-tually do work.

—Greg Hetland, Ph.D.FounderInternational Institute of GeometricDimensioning & Tolerancing (IIGDT)

Measurement uncertainty describes the accuracy of ameasurement result; it is the quantitative evaluation ofthe reasonable values that are associated with a particu-lar measurement. Whether addressing the performancetest results of instruments, or the calibrations of gauges,standard methods for assessing the measurement uncer-tainty and quantifying the validity of the results can beused as an effective tool to improve measurementprocesses.

Consensus standards like those provided in the ASMEB89.7 documents provide a means to achieve GUM-com-pliant uncertainty statements and a recognized method ofestablishing measurement traceability. As a result, use ofsuch standards reduces ambiguity about the conse-quences of measurement uncertainty and allowsusers to benefit from the established work of expertanalysis; thus avoiding potential pitfalls andreducing costs.

—Steven D. Phillips, Ph.D.Leader, PhysicistLarge-Scale Coordinate Metrology GroupNIST – National Institute of Standards and

Technology

ASME B89 Division 7

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GD&T and Uncertainty

ASME B89.7 Documents

B89.7.2 – 1999

Dimensional MeasurementPlanning

The intent of this Standard is tofacilitate agreement betweensuppliers and customers byspecifying a standard method forassessing the dimensional accept-ability of workpieces. Components

of the method are the preparation of an adequate dimen-sional measurement plan and the use of the plan in mak-ing measurements. The major input to the method isdimensional specifications developed, for example, incompliance with ASME Y14.5 – 2009 Dimensioning & Tol-erancing standard.

B89.7.3.1 – 2001

Guidelines for Decision Rules:Considering MeasurementUncertainty, DeterminingConformance to Specifications

These guidelines provide sugges-tions for decision rules when con-sidering measurement uncertaintyin determining conformance to

specification. Applying these guidelines can assist busi-nesses in avoiding disagreements with customers andsuppliers about conformance to specifications and inmanaging costs associated with conformance decisions.

B89.7.3.2 – 2007

Guidelines for the Evaluationof Dimensional MeasurementUncertainty(An ASME Technical Report)

The primary purpose of this Techni-cal Report is to provide introductoryguidelines for assessing dimensionalmeasurement uncertainty in a man-

ner that is less complex than presented in the Guide tothe Expression of Uncertainty in Measurement (GUM).These guidelines are fully consistent with the GUMmethodology and philosophy. The technical simplifica-tions include not assigning degrees of freedom to uncer-tainty sources, assuming uncorrelated uncertaintysources, and avoiding partial differentiation by alwaysworking with input quantities having units of the measur-and. A detailed discussion is presented on measurementuncertainty concepts that should prove valuable to boththe novice and experienced metrologist. Worked exam-ples, with an emphasis on thermal issues, are provided.

Measurement Uncertainty Standards

For Information:

ASME Standards & CertificationThree Park AvenueNew York, NY 10016-5990 U.S.A.

Fredric Constantino

Phone: +1.212.591.8684Fax: +1.212.591.8501Email: constantinof @ asme.orgWebsite: go.asme.org/B89.7

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Measurement Uncertainty Standards

B89.7.3.3 – 2002

Guidelines for Assessing theReliability of DimensionalMeasurement UncertaintyStatements

The primary purpose of this Techni-cal Report is to provide guidelinesfor assessing the reliability of meas-urement uncertainty statements.

Applying these guidelines can assist businesses in avoid-ing disagreements about measurement uncertainty state-ments and in resolving such disagreements should theyoccur. Disagreements over uncertainty statements involv-ing a single measurement system and multiple measure-ment systems (each having their own uncertaintystatement) are considered. Guidance is provided forexamining uncertainty budgets as the primary methodof assessing their reliability. Additionally, resolution bydirect measurement of the measurand is also discussed.

B89.7.4.1 – 2005

Measurement Uncertaintyand Conformance Testing:Risk Analysis(An ASME Technical Report)

This Technical Report providesguidelines for setting gauging (ortest) limits in support of accept/re-ject decisions in workpiece inspec-

tions, instrument verifications, and general conformancetests where uncertain numerical test results are comparedwith specified requirements. In accepting or rejectingworkpieces or instruments based on the results of inspec-tion measurements, the presence of unavoidable measure-ment uncertainty introduces the risk of making erroneousdecisions. By implementing a decision rule that defines arange of acceptable measurement results, one can balancethe risks of rejecting conforming workpieces or instru-ments and accepting nonconforming ones.

B89.7.5 – 2006

Metrological Traceability ofDimensional Measurements tothe SI Unit of Length(An ASME Technical Report)

The primary purpose of this TechnicalReport is to provide introductoryguidelines for assessing dimensionalmeasurement uncertainty in a man-

ner that is less complex than presented in the Guide tothe Expression of Uncertainty in Measurement (GUM).These guidelines are fully consistent with the GUMmethodology and philosophy. The technical simplificationsinclude not assigning degrees of freedom to uncertaintysources, assuming uncorrelated uncertainty sources, andavoiding partial differentiation by always working withinput quantities having units of the measurand. A detaileddiscussion is presented on measurement uncertaintyconcepts that should prove valuable to both the noviceand experienced metrologist. Worked examples, with anemphasis on thermal issues, are provided.

C ONFORMA NC E ZONE

Lower Spec. Limit

Upper Spec. Limit

STRINGENTACCEPTANCE ZONE

g = hU g = hU

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B89.7.3.1 – DECISION RULES. Conformance zone must beguard banded by magnitude of measurement uncertainty toestablish acceptance zone. Guard banding reduces risk of

accepting non-conforming product.

ASME Related Documents

Y14.5 – 2009

Geometric Dimensioningand Tolerancing

The Y14.5 standard is consideredthe authoritative guideline for thedesign language of geometric di-mensioning nd tolerancing (GD&T.)It establishes uniform practices forstating and interpreting GD&T and

related requirements for use on engineering drawingsand in related documents. GD&T is an essential tool forcommunicating design intent — that parts from technicaldrawings have the desired form, fit, function and inter-changeability. By providing uniformity in drawing specifi-cations and interpretation, GD&T reduces guessworkthroughout the manufacturing process — improving qual-ity, lowering costs, and shortening deliveries.

ASME also offers 12 related standards on GD&T, including:Y14.41 – 2003: Digital Product Definition Data Practices.For more offerings and info, visit: go.asme.org/gdt.

B46.1 – 2009

Surface Texture, SurfaceRoughness,Waviness and Lay

This Standard is concerned with thegeometric irregularities of surfaces.It defines surface texture and itsconstituents: roughness, waviness,and lay. It also defines parametersfor specifying surface texture. The

terms and ratings in this Standard relate to surfaces pro-duced by such means as abrading, casting, coating, cutting,etching, plastic deformation, sintering, wear, erosion, etc.

Look for a new 2010 ASME B46.1 edition, which will in-clude an executive summary presenting the essential is-sues in measuring surface roughness. The 2010 editionwill contain many additions and clarifications over thecurrent edition, and provides in one volume an overallguide to surface roughness measurement including in-strument descriptions, filtering requirement, parameterselection, and harmonization with the new ISO 3-D textureparameters. To order, visit: go.asme.org/B46catalog.

B89.4.10360.2 – 2008

Acceptance Test andReverification Test forCoordinate MeasuringMachines (CMMs) Part 2:CMMs Used for MeasuringLinear Dimensions(Technical Report)

This Technical Report establishes requirements and methodsfor specifying and testing the performance of coordinatemeasuring machines (CMMs) having three linear axesperpendicular to each other and up to one rotary axispositioned arbitrarily with respect to these linear axes.In addition to clarifying the performance evaluation ofCMMs, this Technical Report seeks to facilitate performancecomparisons among machines by unifying terminology,general machine classification, and the treatment ofenvironmental effects.

This is a redesignation and update of B89.4.1-1997. Itwas created to harmonize the B89.4.1 standard with ISO10360.2 by incorporating the entire 10360.2 documentinto it and adding additional requirements that can befound in text boxes throughout the technical report.

To Order:

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ASME B89 Division 7

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About ASMECodes and Standards

ASME is the leading international developer ofcodes and standards associated with the art, science,and practice of mechanical engineering. Startingwith the first issuance of its legendary Boiler &Pressure Vessel Code in 1911, ASME’s codes andstandards have grown to nearly 600 offerings cur-rently in print. These offerings cover a breadth oftopics, including pressure technology, nuclear plants,elevators/escalators, construction, engineering design,standardization, and performance testing.

Developing and revising ASME codes and standardsoccurs year-round. More than 4,000 dedicated volun-teers—engineers, scientists, government officials,and others, but not necessarily members of theSociety—contribute their technical expertise toprotect public safety, while reflecting best practicesof industry. The results of their efforts are beingused in over 100 nations; thus setting the standardfor code-development worldwide.

Standards Development Process

In developing all its codes and standards, ASME em-ploys a consensus-based process that considers theinput of all relevant stakeholders. Due process forall input is assured and monitored. All codes-and-standards development is open to public review atappropriate stages, and the actions of the committeeare documented and completely transparent.ASME’s development process is accredited by TheAmerican National Standards Institute (ANSI), whileits principles are consistent with those of the WorldTrade Organization’s Technical Barriers to TradeAgreement.

Volunteer for ASME B89 Division 7

ASME Codes and Standards enjoys ongoing volunteercontributions from hundreds of leading companies,consultants, academics and government officials.Contributors range from department heads and thetop technical experts in their fields all the way toyoung engineers in their early-career stages. Thismix helps assure that the resulting standards aretruly visionary, while also being practical andapplicable for everyday end-users.

For more information on volunteering, visit:go.asme.org/B89.7

About ASME

ASME helps the global engineering communitydevelop solutions to real world challenges facingall people and our planet. Founded in 1880 as theAmerican Society of Mechanical Engineers, ASMEhas grown to serve 120,000 professional membersin 138 countries. We actively enable inspired collab-oration, knowledge sharing and skill developmentacross all engineering disciplines, all around theworld, while promoting the vital role of the engineerin society.

ASME products and services include our renownedcodes and standards, certification and accreditationprograms, professional publications, technical con-ferences, risk-management tools, government/regu-latory advisory, continuing education and professionaldevelopment programs. These efforts, guided byASME leadership, and powered by our volunteernetworks and staff, help make the world a safer andbetter place, today, and for future generations.

Measurement Uncertainty Standards

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T h r e e P a r k A v e n u e

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ASME Standards and Certifications