NCSL-I Workshop and Symposium San Diego CA Aug 7, 2002 Alternative Paths of Traceability in Dimensional Measurements Dennis A. Swyt Chief, NIST Precision Engineering Division

NIST Precision Engineering Division Length and Dimensional Measurements Responsible for providing practical access to the SI unit of length To support these industries conduct research, provide measurement services, participate in development of industry documentary standards Principal customers are in manufacturing, from aircraft, autos to computers, microelectronics

Contents Introduction Main Alternative Paths for Traceability to Unit of Length for Industrial Dimensional Measurements Documentary “Standards” Dealing with Traceability in Dimensional Measurements Relevant to US New US Standards Committee on Traceability in Dimensional Measurements Conclusion

For Dimensional Measurements Traceability Ultimately Means To A Realization of SI Definition of the Meter Methods 1. Length of path traveled by plane e-m wave in measured time t using l = c · t, where c is the (defined constant) speed of light 2. Length of path between crests of plane e-m wave of frequency f using l = n ·  and f ·  = c where frequency is measured a) directly or b) by comparison with recommended radiation Definition Meter is length of the path traveled by light in vacuum during time interval of 1 / second

Principal Means for Realizing the SI Unit of Length for Dimensional Measurements Start with the definition of the meter Use laser as a frequency-wavelength standard Use high-precision laser interferometry (method 2b) embedded directly into a measuring machine Reference frequency of laser to that of one of recommended radiations, e.g. I-HeNe

Conventional Path of Traceability Traditional path of traceability – proceeding from an NMI primary standard – through an NMI dimensional calibration – through intermediary calibrations – to a shop-floor instrument – where NMI provide calibrations – for each specific measurand – with uncertainty a fraction of that of end user This traditional path is unsustainable for the multiplicity of specific dimensional measurands used in industry which could benefit from well-established traceability

What NIST as an NMI Does at the Top of a Traditional Traceability Chain in Dimensional Measurements invokes the definition of the meter uses a laser for known frequency-wavelength uses interferometry in a measuring system simultaneously – locally realizes unit of length – measures the dimensions of features evaluates the uncertainty documents the procedures carries out an intercomparison achieves traceability “directly to SI” i.e. without use of a dimensional standard calibrated by someone else

What It Is Technologically Feasible for Industry to Do invoke the definition of the meter use a laser of known frequency-wavelength use interferometry in a measuring system simultaneously –locally realize the unit of length –measure dimensions evaluate the uncertainty document the procedures carry out an intercomparison achieve traceability “directly to SI” i.e. without use of dimensional standard calibrated by someone else

Current “Standards” on Traceability in Dimensional Measurements Relevant to US (Correct Me If I’m Wrong) ISO GPSRequires traceability to SI unit of length for industrial measurements of dimensions of manufactured parts VIMGives general high-level definition of traceability which includes undefined terms requiring interpretation GUMGives high-level scheme for representing uncertainty (called for by implication in VIM definition of traceability) ILAC PolicyRequires traceability to SI through an NMI for SI-type measures including length dimensions NCSL-IProvides a definition of intrinsic standard in general without indicating whether or not there is any for length NIST PolicyAsserts that establishing/supporting a claim of traceability is matter between provider & user of measurement result

Some Potential Utility of an Industry Standard on Traceability in Dimensional Measurements Would provide basis for establishment within industry of uniform practices on traceability based on industry consensus standard Would provide basis for industry groups to establish traceability to SI for industry-sector-specific measurement quantities for which NMIs may not provide calibrations Would provide impetus to rationalization of overall system of traceability by development of consensus-basedconcepts, definitions, procedures for practical implementation of VIM Would relieve an NMI of needing to provide unilateral guidance to industry on traceability

Issues Facing Developers of a Potential Standard on Traceability of Industrial Dimensional Measurements IssueVIM-defined traceability requires interpretation that is beyond the reach of practitioners and is open to debate Need A standard on T of IDMs would need to supply interpretation and reduce it to recommended practice in terms appropriate for industrial practitioners consistent with BIPM-NMI usage

Issues Facing Developers of a Potential Standard on Traceability of Industrial Dimensional Measurements (cont) IssueThere is no definitive international technical guidance or standard [e.g. from ISO, BIPM, NMIs, or the like] on establishing traceability of the input quantities of an uncertainty statement for a dimensional measurement for which traceability is claimed e.g. probe force, gage or part temperature, air humidity, coefficient of thermal expansion Need A standard on T of IDMs would need to define the traceability requirements and specify recommended practices for such input quantities

Issues Facing Developers of a Potential Standard on Traceability of Industrial Dimensional Measurements (cont) IssueThere is no definitive international technical guidance or standard e.g. from ISO, BIPM, NMIs, or the like on intrinsic standards and their role in traceability to the SI Need A standard on T of IDMs would need to define intrinsic standards of length, if any, and establish principles on their use

NIST View of Its Mission Role Relative to Traceability in Dimensional Measurements Within the limits of its resources: Realize SI unit of length at highest levels of metrological quality Disseminate the unit through dimensional measurement services with measurands and uncertainties that address US industry needs Participate in development of industrially important documentary standards that specify methods for –making dimensional measurements –evaluating uncertainty in dimensional measurements –establishing traceability in dimensional measurements

New Standards Committee on Traceability in Dimensional Measurements As a result of its view of its role in dimensional measurements, NIST is pro-active in its participation in a new standards committee on traceability The committee is ANSI-ASME B89.7 on “Traceability in Dimensional Measurements” The objective is a standard specifying recommended industrial practices for establishing and defending claims of traceability in dimensional measurements, including alternative paths to the SI

Status of Standards Committee B on Traceability in Dimensional Measurements Just been founded Subcommittee of that on Measurement Uncertainty in turn subcommittee of that on Dimensional Metrology Chairman Dr. Steve Phillips of NIST Soliciting participation domestic and foreign Member from PTB Germany 1st-draft technical report ready for circulation Invite, encourage members of NCSL, NMIs, industry to join

Conclusion Paths to the SI in Dimensional Measurements Traceability in dimensional measurements is taking on greater importance for industry Issues for practitioners include interpretations of VIM, alternative paths to the SI meter, intrinsic standards of length, and traceability of input quantities associated with uncertainty in dimensional measurements Not all of what is needed for technically sound industrial practice in these issue-areas is provided by current documentary standards A US standards committee to address the issue has been established NIST is pro-active with regard to that committee Participation, domestic and international, is invited and encouraged