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A Pragmatic Method for Pass/Fail Conformance Reporting that Complies with ANSI/NCSL Z540.3, ISO/IEC17025, and ILAC-G8
Robert Stern, Michael Dobbert
NCSLI Measure | Vol. 5 No. 1 (2010) | 10.1080/19315775.2010.11721504
Publisher NCSL International | Published 3/1/2010 | Pages 46-51
Abstract: What are the criteria for stating Pass/Fail conformance when calibrating an instrument and comparing the measured results against specifications? The answer depends on regional and regulatory requirements, customer need and
other criteria. This requires calibration service providers to be flexible when reporting calibration results which include Pass/Fail conformance statements. This is especially true when serving a global market. This paper explores the different requirements
or guidelines in standards documents, such as ANSI/NCSL Z540.3-2006, ISO/IEC 17025:2005, ILAC-G8:1996, and EURAMET/cg-15/v.01. Some of these documents are prescriptive, while others provide only minimal guidance subject to interpretation. While many
customers simply want to know pass or fail, these differences lead to variations in the Pass/Fail decision point, in the results labels (Pass/Fail vs. Pass/Indeterminate/Fail), and potentially have an effect on the downstream uncertainty analysis.
This paper presents a non-obvious, yet simple method for expressing statements of Pass/Fail conformance. It employs flexible acceptance limits resulting in straightforward “Pass” and “Fail” conformance labels, with unobtrusive annotation to communicate
additional information required by the standards documents. The result is a concise, uniform method flexible enough to satisfy all of the aforementioned standards, regardless of the chosen acceptance limits.
Guidance Documents on Measurement Uncertainty: An Overview and Critical Analysis
Carla ten Caten , Daniel Homrich da Jornada, Morgana Pizzolato
NCSLI Measure | Vol. 5 No. 1 (2010) | 10.1080/19315775.2010.11721507
Publisher NCSL International | Published 3/1/2010 | Pages 68-76
Abstract: The “Guide to the Expression of Uncertainty in Measurement” (GUM) is considered to be the main reference guidance document about measurement uncertainty. Although the GUM was first published more than 10 years ago, this subject
is still acknowledged as a topic of major concern in metrology and is now also being applied to the field of testing. In order to assist both testing and calibration laboratories in a better understanding and application of the GUM's principles, many
derived guidance documents specific to the GUM have been created by several metrology organizations. Some of these documents are detailed guides with specific fields of application, such as the EURACHEM/CITAC Guide for analytical chemistry. Other
documents are more general, like EA-4/16 which covers any quantitative test. Knowing the advantages and drawbacks of each document and deciding which one to use as a reference document can be a difficult task for any metrologist or test engineer.
In this context, the aim of this paper is to present a brief summary of each of these guidance documents, as well as a critical analysis of their main pros and cons. The paper also presents a comparison of these documents with regard to their field
of application, level of knowledge required by the metrologist, whether practical examples are presented, whether correlation effects are presented, etc. As a result, this paper clarifies the differences, advantages, and limitations of these frequently
applied reference documents, thereby assisting laboratories in deciding which document to use as their reference for measurement uncertainty estimation.
Interlaboratory Comparison of Helium Low Gas Flow Measurements in the Range 10−13 to 10−11 mol/s (10−9 to 10−7 cm3/s)
Dana Defibaugh, James Fedchak , Patrick Abbott
NCSLI Measure | Vol. 5 No. 1 (2010) | 10.1080/19315775.2010.11721506
Publisher NCSL International | Published 3/1/2010 | Pages 58-67
Abstract: An interlaboratory comparison (ILC) of helium low-flow measurement capability was recently completed. The ILC was piloted by the National Institute of Standards and Technology (NIST). The majority of the data was taken over
a period of approximately two years; a final round of data was taken by the pilot laboratory approximately three years after the data from the other participants were collected. The participants included a mix of ten industrial and metrological calibration
laboratories within the United States. The comparison was performed using three helium permeation leak artifacts having different flow rates within the range of 10−13 mol/s to 10−11 mol/s (10−9 to 10−7 cm3/s at 0 °C and 101.33 kPa). Each participant
laboratory was required to measure the helium flow rate of all three artifacts at a nominal artifact temperature of 23 °C, and to submit a report of their results, including a complete uncertainty analysis, to the pilot laboratory. The pilot laboratory
made measurements at the beginning, end, and at three other times during the course of the comparison. The reference values used to compare the flow measurements from each laboratory were defined as the weighted linear fit to the pilot laboratory
measurements. Analysis of the comparison results is presented along with an assessment of each participant's equivalence to the reference value for each flow artifact. The goal of this work is to help the participant laboratories to quantify their
capability in the area of helium low-flow measurements. Information of this sort is often required for quality system documentation and certification by organizations such as the American Association for Laboratory Accreditation (A2LA) and the National
Voluntary Laboratory Accreditation Program (NVLAP).
International Comparison of AC-DC Current Transfer Standards at Frequencies from 200 kHz to 1 MHz
Torsten Funck, Valter Tarasso , Karl-Erik Rydler, Martin Garcocz, Ilya Budovsky, Gernot Heine
NCSLI Measure | Vol. 5 No. 1 (2010) | 10.1080/19315775.2010.11721503
Publisher NCSL International | Published 3/1/2010 | Pages 40-44
Abstract: This paper presents an international comparison of ac-dc current transfer measurements at 10 mA and frequencies up to 1 MHz between four national metrology institutes: NMIA (Australia), PTB (Germany), BEV (Austria) and SP (Sweden).
The agreement between the participants is better than 10 μA/A at 500 kHz and 20 μA/A at 1 MHz. The paper presents the measurement results, as well as an overview of the design and characterisation of the reference standards and measurement systems
used at the four laboratories to achieve this performance.
NIST Determination of Industrial Platinum Resistance Thermometer Hysteresis from −196 °C to 200 °C
W. Ellery Murdock, Gregory Strouse
NCSLI Measure | Vol. 5 No. 1 (2010) | 10.1080/19315775.2010.11721505
Publisher NCSL International | Published 3/1/2010 | Pages 52-56
Abstract: The hysteresis of 26 industrial platinum resistance thermometers (IPRTs) at the ice melting point (ice MP, 0 °C) were investigated over the temperature ranges from −20 °C to 20 °C and from −196 °C to 200 °C. Three different
IPRT probe models constructed with sensor elements from two different companies were used. Element types included two types of coil-in-bore elements (partially-supported and fully-supported) as well as thin-film elements. The hysteresis was determined
from the difference in the R(0 °C) values of the IPRTs after being cycled from 0 °C to 200 °C, back to 0 °C, then to −196 °C, and finally back to 0 °C. Reversible changes in the physical state of the platinum (e.g., strain) lead to hysteresis, manifested
as a difference in R(0 °C) measured on heating and on cooling. A correlation was observed between the thermometer sensor fabrication types and the magnitudes of hysteresis values. The partially-supported, fully-supported, and thin-film sensor-element
types gave maximum hysteresis values of 4.1 mK, 11.1 mK, and 11.2 mK, respectively. In addition to the reversible changes in R(0 °C), irreversible changes in R(0 °C) were observed that exceed the nominal hysteresis values for sensor-element types,
which indicated drift of the sensor elements with thermal cycling.
NIST Lowers Gas Flow Uncertainties to 0.025 % or Less
Aaron Johnson, John Wright
NCSLI Measure | Vol. 5 No. 1 (2010) | 10.1080/19315775.2010.11721502
Publisher NCSL International | Published 3/1/2010 | Pages 30-39
Abstract: The National Institute of Standards and Technology (NIST) has reduced the uncertainty of its 34 L and 677 L Pressure-Volume-Temperature-time (PVTt) primary gas flow standards from 0.050 % to 0.025 % (k = 2) for air flow in the
range from 0.01 slm to 2000 slm. Over the restricted range from 0.1 slm to 1000 slm, the uncertainty was reduced to 0.015 %. The reductions in uncertainty were primarily the result of accurately accounting for the water vapor present in the flowing
air. Additional uncertainty reductions result from improved measurements of the pressure and of the collection tank volumes. The latter two improvements slightly reduced flow uncertainties for dry gases (e.g., N2, Ar, He, and CO2) from 0.030 % to
0.025 % in the wider range.
Automating Data Acquisition on a Mechanical Equal-Arm Balance Used in Large Mass Calibrations
Kevin Chesnutwood
NCSLI Measure | Vol. 5 No. 2 (2010) | 10.1080/19315775.2010.11721514
Publisher NCSL International | Published 6/1/2010 | Pages
Abstract: This paper focuses on efforts by the Mass and Force Group at the National Institute of Standards and Technology (NIST) to enhance the data taking operations of an approximately 40 year-old mechanical two-pan equal-arm balance
used for high-precision mass comparisons in the range from approximately 50 kg to 1134 kg (110 lb to 2500 lb). The repeatability and sensitivity of this manually operated balance (called the Russell balance) is exceptional and therefore, the balance
remains a core component of the NIST large mass laboratory. In order to enhance the data taking procedure and reduce the potential uncertainties inherent with human involvement in the data collection process, an automated system was designed and installed
to obtain the turning points of the balance taken during calibration that ultimately are used to convert scale units to SI mass units. This paper discusses the advantages of the improved system, the challenges that had to be overcome, and the design,
operation, and verification of the automated system.
Impact of the Intra-Africa Metrology System (AFRIMETS) on Intra-African and Global Trade
Donald Masuku, Wynand Louw
NCSLI Measure | Vol. 5 No. 2 (2010) | 10.1080/19315775.2010.11721518
Publisher NCSL International | Published 6/1/2010 | Pages 72-78
Abstract: During 2007, the Intra-Africa Metrology System (AFRIMETS) was formed with the five sub-regional metrology organizations (SRMOs) in Africa as the principal members. Four countries not part of a SRMO also became members (Nigeria,
Egypt, Ethiopia and Ghana), extending the countries represented in AFRIMETS to forty one. In October 2008, AFRIMETS officially became the regional metrology organization (RMO) representing Africa. The membership spans the continent with the important
economic groupings represented through the SRMOs. SADCMET is the largest and most active SRMO. It plays a major role in harmonizing measurement to assist trade within the Southern African Development Community (SADC), the most economically active
sub-region on the continent, and assists in the acceptance of its export products. EAMET, representing the East African Community (EAC), is fast expanding its activities and held several workshops and conferences during 2008 to advance metrology in
the region. In the north MAGMET, representing the Maghreb countries, is pooling the measurement resources of Morocco, Tunisia and Algeria to support trade, especially with the European Union. Much work is needed to advance metrology (and trade) in
the central and western parts of Africa. SOAMET, the secretariat for metrology of the Economic Community of West African States (UEMOA), became active during 2007/2008 and participates in AFRIMETS, but currently lacks the metrology infrastructure
of SADCMET, EAMET and MAGMET. CEMACMET, the metrology sub-region representing the Economic and Monetary Community of Central Africa (CEMAC), currently only exists in name and lacks a formal SRMO structure. During 2009, Egypt was instrumental in establishing
a SRMO in North-Eastern Africa and including the two English speaking countries of Western Africa, Nigeria and Ghana. It is called NEWMET and it is expected that this new SRMO will play an important role in AFRIMETS from 2010 onwards. This paper explores
the impact that SADCMET, EAMET and MAGMET have had on trade within the sub-regions and beyond the borders of Africa, and its potential future impacts. It also explores the potential for metrology to assist the expansion of trade from the central and
western African sub-regions by highlighting how the lack of proper metrology infrastructure negatively impacts the potential for export.
Gabriele Quinti, N. Ravaja, K. Kallinen, G. van der Haijden, S. Harris, T. Goodman, G. Gersak, J. Drnovsek F. Crenna, A. Cancedda, A. Höglund, M. Gröning, B. Berglund, R. Emardson, Leslie Pendrill, B. Rossi
NCSLI Measure | Vol. 5 No. 2 (2010) | 10.1080/19315775.2010.11721515
Publisher NCSL International | Published 6/1/2010 | Pages 42-54
Abstract: The European ‘Measuring the Impossible’ Network MINET promotes new research activities in measurement dependent on human perception and/or interpretation. This includes the perceived attributes of products and services, such
as quality or desirability, and societal parameters such as security and well-being. Work has aimed at consensus about four ‘generic’ metrological issues: (1) Measurement Concepts & Terminology; (2) Measurement Techniques: (3) Measurement Uncertainty;
and (4) Decision-making & Impact Assessment, and how these can be applied specifically to the ‘Measurement of Persons’ in terms of ‘Man as a Measurement Instrument’ and ‘Measuring Man.’ Some of the main achievements of MINET include a research
repository with glossary; training course; book; series of workshops; think tanks and study visits, which have brought together a unique constellation of researchers from physics, metrology, physiology, psychophysics, psychology and sociology. Metrology
(quality-assured measurement) in this area is relatively underdeveloped, despite great potential for innovation, and extends beyond traditional physiological metrology in that it also deals with measurement with all human senses as well as mental
and behavioral processes. This is particularly relevant in applications where humans are an important component of critical systems, where for instance health and safety are at stake.
NIST Calibration Uncertainties of Organic Liquid-in-Glass Thermometers over the Range from −196 °C to 20 °C
Wyatt W. Miller, Gregory Strouse, Christina D. Cross
NCSLI Measure | Vol. 5 No. 2 (2010) | 10.1080/19315775.2010.11721517
Publisher NCSL International | Published 6/1/2010 | Pages 66-71
Abstract: The National Institute of Standards and Technology (NIST) Industrial Thermometer Calibration Laboratory (ITCL) investigated the calibration uncertainties of low-temperature organic-filled liquid-in-glass (LiG) thermometers over
the range from −196 °C to 20 °C. Several characteristics of organic-filled LiG thermometers were investigated in order to develop a new uncertainty budget including the impact of: thermal cycling; short- and long-term repeatability; and drain time
of the fluid in the capillary, all as a function of the calibration temperature. Additionally, how different measurement enclosures affected the measured temperature at −196 °C was investigated. From these results, an uncertainty algorithm was developed
as a function of temperature for total-immersion for organic LiG thermometers from −196 °C to 20 °C. Expanded uncertainties (k = 2) for these thermometers varied from 6.4 °C at −196 °C to 0.2 °C at 20 °C. Over the range from −35 °C to 20 °C, the organic
thermometer uncertainties were twice those of mercury thermometers calibrated at NIST.
Meghan Shilling, Andrew Oliver, Hy D. Tran , Andre Claudet, Todd Bauer
NCSLI Measure | Vol. 5 No. 2 (2010) | 10.1080/19315775.2010.11721516
Publisher NCSL International | Published 6/1/2010 | Pages 56-65
Abstract: A mesoscale dimensional artifact based on silicon bulk micromachining fabrication has been developed and manufactured with the intention of evaluating the artifact both on a high precision coordinate measuring machine (CMM)
and video-probe based measuring systems. This hybrid artifact has features that can be located by both a touch probe and a video probe system with a k = 2 uncertainty of 0.4 pm, more than two times better than a glass reference artifact. Evidence
that this uncertainty could be lowered to as little as 50 nm (k = 2) is presented. While videoprobe based systems are commonly used to inspect mesoscale mechanical components, a video-probe system's certified accuracy is generally much worse than
its repeatability. To solve this problem, an artifact has been developed which can be calibrated using a commercially available high-accuracy tactile system and then be used to calibrate typical production vision-based measurement systems. This allows
for error mapping to a higher degree of accuracy than is possible with a glass reference artifact. Details of the designed features and manufacturing process of the hybrid dimensional artifact are given, and a comparison of the designed features to
the measured features of the manufactured artifact is presented and discussed. Measurement results from vision and touch probe systems are compared and evaluated to determine the capability of the manufactured artifact to serve as a calibration tool
for video-probe systems. An uncertainty analysis for calibration of the artifact using a CMM is presented.
An Interlaboratory Comparison of Multijunction Thermal Converters
Thomas Lipe, Beverly Klemme, James Allen, Timothy Large, Kristopher Onderko
NCSLI Measure | Vol. 5 No. 3 (2010) | 10.1080/19315775.2010.11721527
Publisher NCSL International | Published 9/1/2010 | Pages 52-59
Abstract: The results of an interlaboratory comparison (ILC) of Multijunction Thermal Converters (MJTCs) designed and fabricated by collaborators from the National Institute of Standards and Technology (NIST) and Sandia National Laboratories
are reported at 0.5 V and 2 V over the frequency range from 10 Hz to 1 MHz. The ILC participants are laboratories that have these MJTCs, and include the three U.S. Department of Defense Primary Standards Laboratories and Sandia National Laboratories,
with NIST serving as the pilot laboratory. The traveling standards and ILC protocol are described, along with the results of the ILC. The implications for the participating laboratories and the prospect of using this type of comparison in the NIST
AC-DC Difference Calibration Service are also discussed. This ILC, the first ever of MJTCs outside of national metrology institutes (NMIs), was conducted in accordance with Recommended Practice RP-15, published by NCSLI International, and was completely
successful in meeting the goals and outcomes of RP-15.
NCSLI Utilities Committee RTD Interlaboratory Comparison Over the Temperature Range 0 °C to 232 °C
Richard Brenia
NCSLI Measure | Vol. 5 No. 3 (2010) | 10.1080/19315775.2010.11721526
Publisher NCSL International | Published 9/1/2010 | Pages 44-50
Abstract: The Utilities Committee of NCSL International organized a temperature measurement interlaboratory comparison (ILC) using a 100 Q Resistance Temperature Detector (RTD). Measurements were reported over the range from 0 °C to 232
°C for 12 participating laboratories. The results include participant uncertainties, extraneous data filtering, and a reference value developed by the culmination of participant's reported data. Most of the reported data agreed to the accepted reference
value to within the reverence uncertainty (Accepted value ±; Ureference). In summary, the results of this ILC are a very useful tool for participants to evaluate their temperature measurement techniques.
Report of an Interlaboratory Comparison of Gigaohm Resistance Measurements
Nathan Shattuck, Li Pi Su
NCSLI Measure | Vol. 5 No. 3 (2010) | 10.1080/19315775.2010.11721525
Publisher NCSL International | Published 9/1/2010 | Pages 38-43
Abstract: This paper reports the results of an interlaboratory comparison (ILC) of high value resistance measurements in the range of 1 to 100 GΩ. The ILC was pivoted by the Army Primary Standards Laboratory and included the following
participants: National Institute of Standards and Technology, Ohm-Labs, Inc., Measurements International, Canadian National Research Council (NRC, two laboratories), Sandia National Laboratories, and the Air Force Primary Standards Laboratory. The
ILC provided an appraisal of the capabilities and degree of equivalence of the participant laboratories by measuring a Guildline model 6636 resistance standard. The measurements were performed on three of its six internal resistors (1 GΩ, 10 GΩ, and
100 GΩ).
NCSLI Measure | Vol. 5 No. 3 (2010) | 10.1080/19315775.2010.11721529
Publisher NCSL International | Published 9/1/2010 | Pages 68-73
Abstract: This paper presents techniques that manufacturers can use to set specifications and then describes how a metrologist can use those specifications in calibration. Specifications describe the warranted performance of a product
or the expected accuracy of a measurement standard. From the manufacturer's perspective, specifications must describe performance that can be achieved cost effectively. This paper looks at several statistical issues related to setting specifications.
Techniques for characterizing expected product performance, considerations for drift and performance variation due to external environmental conditions, and the significance of measurement uncertainty are covered. A framework is presented that relates
the expected performance of a product to its specifications while maintaining metrology goals, producibility, and competiveness. For calibration, specifications are often used as Type-B uncertainty estimators. Drawing from the statistical issues related
to setting specifications, this paper discusses the use of product specifications in an uncertainty analysis.
The Development of a Unified Time and Frequency Program in the SIM Region
Michael Lombardi , J. Mauricio Lopez-Romero
NCSLI Measure | Vol. 5 No. 3 (2010) | 10.1080/19315775.2010.11721524
Publisher NCSL International | Published 9/1/2010 | Pages 30-36
Abstract: The Sistema Interamericano de Metrologia (SIM) is one of five major regional metrology organizations (RMOs) recognized by the Bureau International des Poids et Mesures (BIPM). SIM is composed of the national metrology institutes
(NMIs) located in the 34 member nations of the Organization of American States (OAS). Its goal is to create a unified measurement network that extends to the entire SIM region, ensuring the uniformity of measurements and strengthening traceability
throughout North, Central, and South America back to the International System (SI) of units. To help reach this goal, SIM sponsors working groups in ten different metrological fields, including time and frequency. Developing a unified time and frequency
measurement network in the SIM region has been a challenging task, but much progress has been made in recent years and many obstacles have been overcome. This paper summarizes work done by the SIM Time and Frequency Metrology Working Group from 2004
to 2010. It discusses the challenges faced by the working group, the progress made by individual laboratories, and the important role played by metrology education. It also provides an overview of two major achievements of the working group: the SIM
Time Network (SIMTN) and the SIM Time (SIMT) scale.
Uncertainty Management versus Risk Management in Calibration
Jim Salsbury
NCSLI Measure | Vol. 5 No. 3 (2010) | 10.1080/19315775.2010.11721528
Publisher NCSL International | Published 9/1/2010 | Pages 60-67
Abstract: This paper studies the impact of the conformance decision rule used in compliance assessment during the calibration process on the subsequent measurements made using the calibrated measuring instrument. The rules that are evaluated
include the default rule of ISO 14253-1, the recommendations of ILAC-G8, the 2 % probability of false accept (PFA) in ANSI/NCSL Z540.3, the 4:1 test uncertainty ratio (TUR), and the simple and stringent acceptance decision rules of ASME B89.7.3.1.
The results of the analysis indicate that managing the measurement uncertainty from the calibration process, and not risk, can often lead to the most economical and technically valid outcome, and therefore decision rules developed without consideration
of the subsequent measurement may not yield the most cost effective solution. In addition, uncertainty management guard banding is shown to give results that are similar to the guard bands based on managing the 2 % PFA risk. Finally, intriguing questions
centered on the impact of various decision rules on the ability to properly use the instrument specifications in the uncertainty analysis of a subsequent measurement are proposed for additional research.
A 21st Century Model for Providing Measurement Traceability in Africa
Wynand Louw
NCSLI Measure | Vol. 5 No. 4 (2010) | 10.1080/19315775.2010.11721536
Publisher NCSL International | Published 12/1/2010 | Pages 38-45
Abstract: The Intra-Africa Metrology System (AFRIMETS) is in its third year of existence as the Regional Metrology Organization (RMO) for Africa. With the financial support of the National Metrology Institutes (NMIs) of Germany and South
Africa (the PTB and the NMISA), UNIDO (assisted by a sponsorship from NORAD) and the assistance of the BIPM, the OIML, NEPAD, RMOs such as EURAMET and APMP, and NMIs such as LNE (France), NIST (USA) and moral support from many others, the structures
necessary for a fully fledged RMO are in place. Five regional comparisons and two proficiency testing schemes are in progress, various training courses are being conducted and a summer school is in the planning stage. It is a success story accomplished
in a relatively short time, but much remain to be done. There are 43 member countries of AFRIMETS and only a few such as South Africa, Egypt and Kenya participate in international scientific and industrial metrology activities. Others such as Tunisia
and Ghana only recently entered the international metrology world through associate membership of the General Conference of Weights and Measures (CGPM). Another group of about 15 countries have well established national metrology institutes and participate
in regional metrology activities in both legal and scientific and industrial metrology. This leaves about half of the member countries with some legal metrology facilities and in the process of developing their scientific and industrial metrology
capabilities, or establishing NMIs.
A Method For Assessing & Demonstrating The Impact Of Knowledge Transfer
Tim Jones, Phil Cooper, Francis Tuffy, Jenny Hully
NCSLI Measure | Vol. 5 No. 4 (2010) | 10.1080/19315775.2010.11721539
Publisher NCSL International | Published 12/1/2010 | Pages 64-71
Abstract: The National Physical Laboratory (NPL) is provided with public and private funding to develop and apply the UK's National Measurement System. The level of funding dedicated to assisting with the translation of knowledge from
public sector investment in research to industry has increased over the past decade in the UK. This investment has resulted in a rapid growth in actively managed knowledge transfer, leading to increasing demands for this investment to provide evidence
of impact. NPL has developed a contextual framework for understanding the range of knowledge transfer activities it provides in response to its complex drivers as both a Public Sector Research Establishment and a Research & Technology Organisation.
This paper outlines and reviews a range of methods for measuring the impact of knowledge transfer. It provides insights into the Value Scorecard methodology developed at NPL in response to the complexity of formulating and validating future knowledge
and technology transfer activities in the field of measurement.
A NIST Disciplined Oscillator: Delivering UTC(NIST) to the Calibration Laboratory
Michael Lombardi
NCSLI Measure | Vol. 5 No. 4 (2010) | 10.1080/19315775.2010.11721537
Publisher NCSL International | Published 12/1/2010 | Pages 46-54
Abstract: The National Institute of Standards and Technology (NIST) now offers a service that provides customers with an oscillator locked to UTC(NIST), the United States national standard for frequency and time. A NIST disciplined oscillator
(NISTDO) works by utilizing both the Internet and “common-view” observations of Global Positioning System (GPS) satellites, and can serve as the primary frequency and time standard for a calibration or metrology laboratory. NISTDOs are directly referenced
to the Coordinated Universal Time scale kept at NIST, known as UTC(NIST). This makes it easy for laboratories to establish traceability to the International System directly through NIST. Customers are provided with standard frequency outputs of 5
MHz and/or 10 MHz, as well as timing outputs of 1 pulse per second. These outputs provide frequency with an uncertainty ofss ≈1 × 10−14 (k = 2) when averaged over a 24-hour interval, and time with an uncertainty near 10 ns (k = 2) with respect to
UTC(NIST). This paper discusses the theory of operation of the NISTDO, and demonstrates the accuracy and stability of the device over both short and long time intervals.
NCSLI Measure | Vol. 5 No. 4 (2010) | 10.1080/19315775.2010.11721538
Publisher NCSL International | Published 12/1/2010 | Pages 56-62
Abstract: NRC offers calibration of ac shunts from milliamperes up to 100 A, in the 10 Hz to 100 kHz frequency band, with expanded uncertainties between 10 μA/A for currents in the milliampere range to 50 μA/A at 100 A and 100 kHz. The
paper describes the design of NRC ac standard shunts, as well as NRC experience in calibrations of commercial shunts. The ac-dc difference of some commercial low current shunts is load sensitive at higher frequency ranges. The paper discusses reasons
for this sensitivity and suggests mitigating solutions.
The 2008 NCSLI Josephson Voltage Standards Interlaboratory Comparison
Leonard Pardo, Yi-Hua Tang, Curtis Kiser, William Miller, Harold Parks, Clark Hamilton
NCSLI Measure | Vol. 5 No. 4 (2010) | 10.1080/19315775.2010.11721540
Publisher NCSL International | Published 12/1/2010 | Pages 72-76
Abstract: Josephson voltage standards (JVS) provide a highly accurate representation of the volt. Although the Josephson Effect provides an intrinsic standard of voltage, intercomparisons between different systems are important to insure
that potential sources of systematic error are under control and to provide an explicit link to the volt as maintained by a national metrology institute. The results from the 8th Josephson voltage standards interlaboratory comparison (ILC) sponsored
by the National Conference of Standards Laboratories International (NCSLI) are presented and compared with the results of the previous three ILC's which used the same Zener standards and protocols. The 8th interlaboratory comparison was conducted
between March and July, 2008 with 14 participating laboratories in North America. It began with direct array-to-array comparison between the National Institute of Standards and Technology (NIST) compact Josephson voltage standard (CJVS) system and
the pivot laboratory system at Lockheed Martin Mission Services in Denver. The two systems agreed to well within the k = 2 uncertainty of the comparison of 6.6 nV at 10 V. Once the NIST-pivot laboratory comparison was complete, four traveling Zeners
were sent from the pivot laboratory to the participant laboratories in a series of four loops with a pivot laboratory measurement between the loops. The standard deviation of the 10 V bank average as measured by the participants with respect to the
drift line established by the pivot laboratory was 68 nV. There were some indications of non-normal behavior in the residuals and an expanded uncertainty for the comparison of 190 nV at a 95 % level of confidence was adopted.
The NPL Training Framework: Latest Developments in Dimensional and Large Volume Metrology Training
Tom Ashby
NCSLI Measure | Vol. 5 No. 4 (2010) | 10.1080/19315775.2010.11721535
Publisher NCSL International | Published 12/1/2010 | Pages 34-37
Abstract: This paper covers the latest developments in training from the National Physical Laboratory (NPL) as it continues to expand overseas into the USA market and beyond. NPL has been developing an industrially relevant commercial
training business for over three years. This involves the development and promotion of the NPL Training Framework to key customers and stakeholders, listening to and engaging with both industry and academia with the ultimate goal of creating a set
of nationally recognised qualifications in metrology that employers and employees aspire to: a certified group of metrologists. The NPL Training Framework currently includes units in Dimensional Measurement and Large Volume Metrology. In addition,
NPL offers its extensive capability as a training consultant for bespoke training and development projects both nationally and internationally. Work-based learning can have significant benefits for an organisation, including increased loyalty, motivation
and productivity.
