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Measure Articles 2009 (20)

 
Picture of the productA 10 Volt “Turnkey” Programmable Josephson Voltage Stand.
C. J. Burroughs, A. Rüfenacht, P. D. Dresselhaus, S. P. Benz and M. M. Elsbury
The output voltage of Programmable Josephson Voltage Standard (PJVS) circuits has reached the 10 V benchmark, which was set over twenty years ago by conventional dc Josephson Voltage Standard (JVS) systems. The nonhysteretic Josephson junctions in these next-generation 10 V PJVS systems provide a number of advantages and additional features as compared to conventional JVS systems. Most importantly, the new PJVS system will have comprehensive “turnkey” automation and be able to fully characterize all operating margins of the device without operator participation. Inherent voltage-step stability and large current margins (1 mA), which eliminate the need for output filters, will enable new applications not previously possible with conventional JVS. Rapid settling time (200 ns) will enable the generation of both dc and stepwise-approximated ac voltages that will be metrologically useful up to a few hundred hertz. The lower microwave drive frequency (20 GHz instead of 75 GHz) will reduce cost and improve reliability of the system.


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MS09_03_BURROUG
Picture of the productA Direct Josephson Voltage Standard Comparison
Yi-hua Tang, William B. Miller and Leonard P. Pardo
To support the 8th JVS Interlaboratory Comparison (ILC) in 2008, sponsored by the National Conference of Standard Laboratories International (NCSLI), a direct Josephson Voltage Standard (JVS) comparison using the National Institute of Standards and Technology (NIST) compact JVS (CJVS) was carried out in March 2008 between the National Institute of Standards and Technology (NIST) and the Lockheed Martin Mission Services (LMMS). LMMS was the pivot laboratory for the JVS ILC 2008. A comparison between NIST and LMMS provides all of the JVS ILC participating laboratories with a link to NIST. The protocol designed for the JVS direct comparison between NIST and LMMS is described in this paper. It was possible to use a direct JVS comparison to detect JVS system errors associated with the frequency measurement, cryoprobe leakage correction and the Josephson junction array. These errors were small in magnitude and were not normally detectable by other types of JVS comparisons, such as the Zener Measurement Assurance Program (MAP). The difference between the LMMS JVS and the NIST CJVS at 10 V was found to be 0.71 nV with an expanded uncertainty of 6.6 nV (k = 2) or a relative uncertainty of 6.6 parts in 1010, which was a factor of four improvement compared to that of the in-situ indirect JVS comparisons implemented in the NCSLI JVS ILC 2005 and a factor of about 40 improvement compared to the results from the NCSLI JVS ILC 2002. This comparison has verified the LMMS JVS and also has confirmed that LMMS was well prepared to serve as the pivot laboratory for the NCSLI JVS ILC 2008.


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MS09_03_TANG
Picture of the productA Measurement Standard for Evaluating Metrology Positions
Danny Newcombe and Susan Reynolds
Metrologists have traditionally been at a disadvantage in job evaluations because of a dearth of comparable positions within their job market. Additionally, many Human Resource (HR) professionals are not familiar enough with the field of metrology to effectively compare the job requirements to occupations with which they have more experience. The resulting inequities in pay contribute to difficulties in recruitment and retention of aspiring Metrologists. HR professionals commonly use methods known as Analytical Job Evaluation Systems. This approach is similar to a Metrologist comparing an artifact to a standard when assigning a value to an unknown. This paper describes the development and application of a method to evaluate a Metrologist’s job using comparisons to occupations that HR professionals are much more familiar with. Developing an evaluation tool that HR would find credible and reliable depended upon finding clear, reasonable “standards” from an independent and highly regarded source, such as the United States Department of Labor Office of Administrative Law Judges Law Library which includes exactly the impartial and respected reference required. The occupational ratings contained in this library include detailed comparisons of the skills and knowledge required to perform many different jobs. Each occupation is rated in three different educational developmental categories: reasoning, mathematical, and language skills development levels. Specific vocational preparation is also quantified. This system, using standardized criteria, evaluates the Metrologist job title along with many other occupations that are much more commonly known. The methods and strategies described in this paper were critical elements of a job reevaluation request submitted for the Maine State Metrologist. The analysis resulted in a wage reallocation that aligned the pay grade level to a more equitable position relative to other technical professionals within Maine State Government. Top management and HR professionals found the comparisons to be clear and flawless. This method may be generalized across the spectrum of metrology related positions from entry level to advanced. The wide variety of occupations rated within the “reference standard” ensures that most organizations will find one or more familiar job titles to use as a basis of comparison.


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MS09_01_NEWCOMB
Picture of the productAssessment of Laboratory Performance in External Prof.
Sanjay Yadav and A. K. Bandyopadhyay
This report describes the proficiency testing for pressure measurements of fourteen laboratories that are accredited by the National Accreditation Board for Testing and Calibration of Laboratories (NABL) and have a best measurement capability that is greater than 0.25 % of full-scale pressure. The artifact used for the comparison was a dial gauge covering the pressure range 6 to 60 MPa. The primary objective was to assess the laboratory’s technical competence to perform measurements and also to assess the compatibility of results submitted by the laboratories. This programme, which was identified by code number NABL-Pressure-PT007, was coordinated by the National Physical Laboratory, New Delhi, which also acted as the reference laboratory. The program started in May, 2006 and was completed during October, 2007. The comparison was carried out at ten evenly chosen pressure points throughout the 6 to 60 MPa range. Out of the total 117 measurement results reported, 81% were found in agreement with the results of the reference laboratory. However, five of the laboratories had three or more values outside acceptable limits and have been requested to review their pressure measurement process. Two of the five laboratories reported the improper working of their master instruments, two laboratories underestimated their measurement uncertainty, and the fifth laboratory has not yet responded. Overall, the results were considered to be good, since this was the first proficiency testing for most of the participating laboratories.


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MS09_01_YADAV
Picture of the productBenefits Obtained by Participation in, and Organization
Hugo Ent and Oswin Kerkhof
Laboratories continually strive to ensure the quality of instruments, procedures, and capabilities. No matter how carefully they conduct these internal checks, systematic deviations often go unnoticed. It is therefore important that they regularly compare their measurement results with those of other laboratories (benchmarking). Participation in interlaboratory comparisons is a vital investment in reliability, operational certitude, and staff confidence. NMi Van Swinden Laboratory (NMi VSL), the Dutch national institute for metrology, has more than 30 years of experience in interlaboratory comparisons. NMi VSL is accredited to organize interlaboratory comparisons. Highlighted will be 12.5 years of yearly comparisons between NIST (USA) and NMi VSL (The Netherlands) to support the Declaration of Equivalence between NIST and NMi VSL in the gas analysis field. Furthermore, results will be presented of a major gas analysis interlaboratory scheme that NMi VSL is organizing for the worldwide production locations of oil company Shell. We started this exercise in 2003 and the very good news is, that the scheme recently became completely open. As such any laboratory is welcome to join the scheme. Based upon the success of the now called Correlation Scheme, NMi VSL started a marketing theme group to explore possibilities for a wider participation in interlaboratory comparisons. Although ISO/IEC 17025 requires participation, laboratories are not very willing to participate freely! Measurement precision is a hidden quality at all laboratories. It usually attracts attention if measurements fail to match those of other laboratories, indicating that there might be some kind of problem. Prior to that, no news is good news. So, how can we raise awareness? Ideas to achieve this are presented.


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MS09_02_ENT
Picture of the productCalibration and Uncertainty Analysis of Predictions
Blaza Toman
Computer experiments are simulations of physical experiments performed by exercising a mathematical model for a physical or chemical process, to produce model outputs corresponding to sets of values of inputs to the model. They are especially useful when the corresponding physical experiments are difficult or expensive. In these cases one will perform a relatively small number of physical experiments that are used to calibrate the simulation model. This is then employed to explore the space of values of the inputs extensively, in a way that “interpolates” the results of the physical experiments. Quantification of uncertainty for the outputs of such computer experiments is of great interest. The sources of uncertainty are in part due to the experimental measurement uncertainty in the inputs, and in part due to inadequacies of the underlying mathematical model. This paper presents methods for calibration and assessment of both types of uncertainty and demonstrates their use on two simple fire models.


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MS09_01_TOMAN
Picture of the productCooperation in the Development of National Metrology
Wolfgang Schmid and Arnold Leitner
Growing participation of emerging economies in global markets brings with it the need for these countries to demonstrate the conformity of the products produced by their industries with standards and requirements of their customers. The establishment of a functioning and internationally recognised national quality infrastructure, with metrology forming an essential part of it, is crucial for these countries. The European Association of National Metrology Institutes, EURAMET, as a Regional Metrology Organisation (RMO) of Europe, recognises this responsibility and has organised advisory support and the exchange of experience among its members, as well as searching for a harmonised metrology infrastructure in Europe. The members of EURAMET (comprising full members and associates) are the National Metrology Institutes (NMIs) and Designated Institutes, which are responsible for maintaining the national measurement standards, facilitating traceability to the International System of Units (SI), and providing knowledge transfer to the users of metrology in their countries. Many members of EURAMET are from countries where the national quality infrastructure is still under development. Aiming at a greater efficiency in this development process, a few years ago the NMIs from South-East Europe started a closer cooperation via joint activities and sharing experiences. With the establishment of a EURAMET Focus Group for “Facilitating National Metrology Infrastructure Development,” this cooperation was opened to all EURAMET members. The first meeting of the Focus Group was held in November 2008 in Skopje, FYR Macedonia. The three objectives of the Focus Group are: (1) The promotion and the development of the metrology infrastructure in the countries of its members by increased cooperation. (2) The facilitation and acceleration of the integration of its member NMIs into EURAMET activities bridging the gap between small and new NMIs to the leading NMIs. (3) Raising awareness about the development of metrology and quality infrastructure in the countries. This paper describes the history of the cooperation, introduces the objectives and Terms of Reference of the Focus Group, and describes the activities which were planned and initiated at its first meeting.


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MS09_04_SCHMID
Picture of the productDesign and Performance of the New NIST Hybrid Hum. Gen.
C. W. Meyer, W. W. Miller, D. C. Ripple and G. E. Scace
A new humidity generator has been constructed at the National Institute of Standards and Technology and is now fully operational. The NIST Hybrid Humidity Generator (HHG) has replaced the Two-Pressure (2-P) Humidity Generator Mark II as the NIST primary humidity generation standard for frost/dew points from -70 °C to +25 °C using calibration gas flows up to 150 standard liters per minute. The HHG extends the NIST humidity generation range up to 85 °C, and outperforms the 2-P Generator in terms of accuracy. The HHG combines the two-pressure and dividedflow humidity generation techniques (hence the name “hybrid”). The centerpiece of the HHG is a heat-exchanger/saturator that is immersed in a temperature-controlled bath stable to within 1 mK. A precisely regulated pre-saturation process minimizes sensible and latent heat loading on the final saturator. For dew/frost point temperatures above -15 °C, the two-pressure principle is employed. For frost points at or below -15 °C, the divided-flow method is used. For this method, the water-vapor/air mixture is produced by mixing metered streams of moist air produced by the two-pressure principle with purified, dry air; here, the HHG saturates the wet air stream at a temperature close to the water triple point, reducing the uncertainty of the water vapor pressure. To our knowledge, this is the first primary generator that incorporates the divided-flow technique. The design of the HHG is described, as well as the estimated uncertainty of the dew/frost-point and mole fraction of moist air it generates. The uncertainty estimate is based on a series of performance tests performed on the HHG. Finally, the humidity generated by the HHG is compared to the humidity generated by the other NIST humidity-generation standards.


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MS09_02_MEYER
Picture of the productDevelopment of Primary Frequency Standards, CENAM
S. López-López, J. M. López-Romero, E. de Carlos-López, M. Talavera-Ortega and N. Shtin
The Centro Nacional de Metrologia, CENAM, has developed an optically pumped cesium beam frequency standard, CsOP-1, and is close to completing a cold atom fountain primary clock, CsF-1. Evaluation of the major systematic frequency shifts in the CsOP-1 has been completed. In order to improve its accuracy, the linewidth of the central Ramsey fringe has been reduced from 1 kHz down to around 100 Hz. The clock is currently undergoing major changes to its Ramsey Cavity and the fractional frequency uncertainty is expected to be a few parts in 1014. The CsF-1 clock under development uses distributed Bragg reflector (DBR) diode lasers in the optical system of the magneto optical trap (MOT). The MOT is robust against mechanical vibration, acoustic noise and temperature changes in the laboratory, since DBR diode lasers do not have an extended cavity aim at reducing the linewidth. Characterization of the MOT as a function of several operation parameters, such as intensity of beams, beam diameter and gradient of the magnetic field, has been made. Measurement of the number of trapped Cs atoms in our Cs MOT was near 6 ×107. Magnetic shielding of the flight region has been designed and built as well as of the microwave cavity. Sapphire oscillators, which will be used as local oscillators for both of the primary frequency standards, have been designed and built. Fractional frequency uncertainty on the CsF-1 clock is expected to be a few parts in 1015.


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MS09_03_LOPEZ
Picture of the productEffect of Dissolved Nitrogen Gas on the Density of Di-2-Et
J. H. Hendricks, J. R. Ricker, J. H. Chow and D. A. Olson
The National Institute of Standards and Technology (NIST) Low Pressure Manometry Laboratory maintains national pressure standards ranging from 1 mPa to 360 kPa through the operation of four ultrasonic interferometer manometer (UIM) pressure standards. NIST’s newest UIM standard operates with Di-2-ethylhexyl sebacate (DEHS) oil as the working fluid over the range of 1 mPa to 140 Pa in absolute mode. The relative change in density of DEHS oil as a function of nitrogen gas pressure was determined using a vibrating-tube densimeter with measurement repeatability of 1 × 10-6 g/cm3 and measurement accuracy of 5 × 10-6 g/cm3 given by the instrument manufacturer. The densimeter was modified to operate at pressures below one atmosphere. The density of DEHS oil was observed to follow a linear dependence with the pressure of nitrogen gas exposure. The difference or change in density of DEHS oil after vacuum exposure (≤ 8 × 10-4 Pa) and pressures ranging from 138 Pa to 101 kPa was evaluated. For the pressures up to 1.367 kPa, there was no statistically significant change in the oil density observed. However, exposure to pressures between 10 kPa and 101 kPa showed significant density changes. The density of DEHS oil decreased by 46 ppm ± 5 ppm after 2 h of nitrogen gas exposure at 101 kPa. The density of DEHS oil decreased by 42 ppm ± 3 ppm after more than 24 h air exposure at 101 kPa. The results of this study show that the effect of dissolved gas on the density of DEHS oil does not contribute significantly to the pressure dependent uncertainty of the NIST oil UIM when operated over its range of 1 mPa to 140 Pa in absolute mode. Additionally, the results demonstrate that the oil density change is small enough that an oil manometer with an extended range of 1.4 kPa (10 torr) would not be adversely impacted by this gas density effect.


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MS09_02_HENDRIC
Picture of the productEURAMET: European Association of National Metrology Inst.
Leslie R. Pendrill
Intensified cooperation amongst the national metrology institutes of Europe in all their fields of activity, from metrological research to calibration services, is a response to increased needs of society for traceable measurement, not only in the traditional areas (trade, manufacturing) but also in meeting the ´Grand Challenges’ of modern society, such as Energy & the Environment; Health and Security, often in combination with the enabling technologies. European metrology had been coordinated successfully since 1987 by the European Association of National Metrology Institutes (EUROMET) but with increased integration of national programmes, a change of organisational form became necessary and since 2007 EURAMET e.V. is its successor as the Regional Metrology Organisation (RMO) of Europe. Increased cooperation means not merely adding together the sum of the national metrology programmes but even integrating resources, at least partially, in a truly regional programme. Alongside other EURAMET developments such as the European Metrology Research Programme and increasing support to metrological infrastructures reported elsewhere in this journal, the present paper will highlight other important EURAMET activities:


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MS09_04_PENDRIL
Picture of the productExtending the Calibration Interval for Self-Adjusting Test
Wayne Goeke
Self-adjusting (or “artifact calibrating”) instruments have become commonplace among today’s test equipment. On one hand, the ability to adjust the entire instrument using only a few traceable artifact standards simplifies the adjustment process. On the other hand, periodic full verification is still required for these instruments and this process still requires many traceable reference values to ensure the instrument’s internal self-adjustment process has been performed properly. As a result, the cost of a fully traceable calibration that includes verification of every function and range of these instruments can be considerable, despite the simplified and more economical adjustment process. This paper discusses the theory underlying an inter-comparison/verification method for extending the calibration interval without increasing the risk of incurring an undetected out-of-tolerance condition and provides an experimental example of the method. Inter-comparing multiple self-adjusting instruments after self-adjustment has been performed increases confidence that the self-adjustment process for each instrument has worked correctly. This increased confidence may allow extending the calibration interval while maintaining assurance that instruments are within tolerance. The extended calibration interval may yield a significant reduction in the cost of maintaining a pool of self-adjusting instruments.


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MS09_02_GOEKE
Picture of the productHomogeneity Issues in Proficiency Testing for Calib. Lab.
Jeff C. Gust
This paper presents the technical issues concerning the homogeneity and stability of artifacts that are used primarily for proficiency testing of calibration laboratories. Additionally, one of the key performance metrics in proficiency testing, the normalized error formula, is analyzed and inadequacies in the formula are identified. This paper makes consensus recommendations concerning the resolution of these issues. These recommendations are intended for use as guidance for the application of a proficiency testing scheme that meets the requirements of ISO/IEC Guide 43-1:1997, ILAC G13:2000 and possibly the standard in development, ISO 17043.


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MS09_01_GUST
Picture of the productMetrology and Testing in Materials Science and Technology
Horst Czichos
This article reviews materials metrology and testing. At the outset, an overview on the nature and the types of materials from the macroscale to the nanoscale is given. Then the principles, methods and instruments to characterise the basic features of materials - composition, microstructure, properties, and performance - are presented. Finally, reference materials and reference procedures are described as a means for materials measurements traceability to standards, and as tools to control the reliability and safety of materials in different applications.


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MS09_04_CZICHOS
Picture of the productNorth American One Gigaohm Interlaboratory Comparison
Jay Klevens
Increasingly accurate high resistance measurements are required in electronic measurements. In order to verify these measurements, an interlaboratory comparison (ILC) was conducted at the 1 gigaohm (109 ohms) resistance level. Participants in the U. S. and Canada included manufacturers, commercial calibration laboratories, and government laboratories. Six different measurement methods were used; all six methods were validated by the ILC. The National Institute of Standards and Technology performed the opening and closing measurements on the artifacts. NCSL International provided generous support of this ILC. This paper presents the results, the methods, and the participant’s associated uncertainties. Some recommendations are offered for developing more consistent uncertainty determinations for various measurement techniques and for developing a better understanding of leakage currents at high resistance measurements and guarding against them.


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MS09_01_KLEVENS
Picture of the productProcedures for the Traceability of High Resistance Stand.
Dean G. Jarrett, Marlin Kraft, Isabel Castro, Brett Degler and Mark Evans
The Metrology of the Ohm Project in the Quantum Electrical Metrology Division at the National Institute of Standards and Technology (NIST) routinely disseminates the U. S. representation of the ohm through calibration services and measurement assurance programs. The measurement systems and procedures used to calibrate standard resistors and current shunts of nominal decade values in the range 10-5 Ω to 1012 Ω provide NIST customers with traceability to U. S. and international standards based on the quantum Hall effect. In recent years, a number of requests have been received regarding the best practices for dissemination of high resistance (107 Ω to 1012 Ω ) from primary standard resistors calibrated by NIST to secondary standard resistors calibrated by our customers. The availability of a new generation of high resistance bridges, meters, and instruments with improved specifications, microprocessor based automation, software packages, and programmable parameters has given the measurement community more options for this dissemination, but has also raised many questions regarding how to best disseminate the ohm in the high resistance range. Over the past year, NIST has worked with several customers and manufacturers to develop a set of procedures to meet today’s needs for disseminating the ohm at high resistance values. NIST has provided designs and guidance for the development of improved high resistance standards with low voltage coefficients, low temperature coefficients, low drift rates, rapid settling times, and guarded components. Customers, such as the U. S. Department of Defense primary standards laboratories and Costa Rica’s National Metrology Institute Laboratorio Costarricense de Metrologia and the Instituto Costarricense de Electricidad, have asked for guidance in supporting their ability to maintain and disseminate the ohm from the NIST calibrations of their primary high resistance standards to secondary standards laboratories using a digital teraohmmeter as the transfer device. NIST, our customers, and the teraohmmeter manufacturer have worked together to develop procedures and make the necessary measurements to meet customers’ needs for traceability to NIST by using the teraohmmeter as a transfer device.


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MS09_01_JARRETT
Picture of the productSensitivity Drift Behaviour of Precision Mass Comparator
Shih Mean LEE and David, Lee Kwee LIM
The sensitivity of commercially available precision mass comparators used for the calibration of high accuracy stainless steel weights are usually adjusted using either external or internal stainless steel weights. This procedure works well when stainless steel weights are calibrated against stainless steel reference mass standards. When a Pt-Ir prototype mass standard is used as reference standard instead, the buoyancy effect arising from the large difference in the density of the two materials will magnify the error contribution due to the sensitivity characteristics behaviour of the mass comparator, affecting the measurement result and its associated uncertainty. Although the sensitivity can be determined externally through a series of comparative weighings involving the prototype reference, its behaviour is still not well appreciated. A series of experiments are carried out to study this behavior and the influence factors associated with it. The experimental results will be used to identify possible ways to minimize the undesirable effect arising from the sensitivity drift, and to recommend better methods for weighing Pt-Ir using a commercially available high precision mass comparator.


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MS09_03_LEE
Picture of the productThe Design and Calibration of Rogowski Coils
Branislav Djokic
In spite of a large number of publications on new Rogowski coil designs and applications, there are relatively few papers that deal with their calibration, and even fewer that address the traceability of these calibrations. This paper describes some of the improvements in the design and performance of Rogowski coils. It focuses on the calibration methods and the traceability required by more demanding applications of the improved Rogowski coil. An overview of the calibration capabilities regarding current and frequency ranges is presented. The best uncertainties (k = 2) of the advanced calibration systems described in the paper are estimated to be better than 50 µA/A for magnitude and 50 µrad for phase, at power frequencies. The uncertainties increase with frequency and current. The capability of calibration systems to generate high currents decreases with increasing frequency.


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MS09_02_DJOKIC
Picture of the productThe European Metrology Research Programme in Action
Andy Henson, Michael Kühne and Luc Erard
As the new millennium dawned, the European national metrology institutes (NMIs) were faced with what we now refer to as the “European metrology dilemma.” Demands for wider scope and greater precision from traditional stakeholders, the need to support emerging areas such as biotechnology and nanotechnology, and the greater demand from established areas such as food safety, clinical medicine and environment, whilst public funding was broadly static, requiring a paradigm shift in the way we operated. The European Metrology Research Programme, the EMRP, allows Europe to assemble critical mass amongst the NMIs to tackle major research projects in a coordinated and collaborative manner addressing fundamental metrology, metrology for industry and innovation, and metrology improving the quality of life. The EMRP became a reality with the first phase of 21 Joint Research Projects, selected through an independent evaluation process and totaling some 64.6 M€, launched between February and July 2008. The second much larger phase began when the first call for potential research topics, addressing metrology needs in the energy sector, was launched in May 2009. This 400 M€second phase will run over a number of years with annual calls; it uses a major instrument of integration, that is Article 169 of the European Treaty. The EMRP is jointly funded by the European Commission and the 22 participating countries. This paper updates progress on the first phase and second phase of the EMRP, whilst reflecting on the challenges and critical success factors associated with launching large-scale programme level collaborative ventures.


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MS09_04_HENSON
Picture of the productUncalibrated Helium-Neon Lasers in Length Metrology
Jack A. Stone
The vacuum wavelength of a gas laser cannot vary from its central value by more than a few parts in 106. Consequently, an uncertainty of this magnitude can be assigned for the wavelength of the laser even if it has not been calibrated and even if the laser is not frequency stabilized. When this uncertainty is satisfactory for a specific application, calibration of the laser’s vacuum wavelength provides no apparent benefit and, from a logical standpoint, should not be required. The wavelength uncertainty of uncalibrated or unstabilized helium neon lasers has been carefully evaluated by an ad hoc subcommittee of the CCL (Consultative Committee for Length) of the International Committee on Weights and Measures (CIPM). The CCL has recommended that unstabilized or uncalibrated helium-neon lasers operating at 633 nm should be included in the new list of standard frequencies, “Recommended values of standard frequencies for applications including the practical realization of the metre and secondary representations of the second.” Among other functions, this new list replaces the “Mise en Pratique for the definition of the metre” as the authoritative document assigning accepted values and uncertainties for laser radiations of interest for length metrology. The adopted value for vacuum wavelength of an uncalibrated helium-neon laser is 632.990 8 nm, and the relative standard uncertainty is 1.5 × 10-6. This paper reviews the work of the CCL subcommittee, discusses the technical basis for assigning a wavelength and uncertainty to the 633 nm radiation, considers the need for documentary standards, and describes what additional steps are required to have confidence in measurements when the traceability of the basic length unit is provided by an uncalibrated laser. An uncalibrated laser can often be employed with full confidence for a measurement, but it is important to realize that the laser does not, by itself, guarantee successful measurement results; there are almost always additional steps required to verify measurement uncertainty, whether the laser is calibrated or not.


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MS09_03_STONE