| 1. |
- Janssen, T J B M, et al.
(author)
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Precision comparison of the quantum Hall effect in graphene and gallium arsenide
- 2012
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In: Metrologia. - : Institute of Physics. - 0026-1394 .- 1681-7575. ; 49:3, s. 294-306
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Journal article (peer-reviewed)abstract
- The half-integer quantum Hall effect in epitaxial graphene is compared with high precision to the well-known integer effect in a GaAs/AlGaAs heterostructure. We find no difference between the quantized resistance values within the relative standard uncertainty of our measurement of 8.7 x 10(-11). The result places new tighter limits on any possible correction terms to the simple relation R-K = h/e(2), and also demonstrates that epitaxial graphene samples are suitable for application as electrical resistance standards of the highest metrological quality. We discuss the characterization of the graphene sample used in this experiment and present the details of the cryogenic current comparator bridge and associated uncertainty budget.
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| 2. |
- Bich, Walter, et al.
(author)
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Revision of the 'Guide to the Expression of Uncertainty in Measurement'
- 2012
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In: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 49:6, s. 702-705
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Journal article (peer-reviewed)abstract
- The Joint Committee for Guides in Metrology, Working Group 1, JCGM-WG1, is currently revising the 'Guide to the Expression of Uncertainty in Measurement'. In this communication, the motivation for undertaking such a revision is given and the main changes with respect to the current, 2008 edition are outlined.
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| 3. |
- Bodnar, Olha, senior lecturer, 1979-, et al.
(author)
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On the adjustment of inconsistent data using the Birge ratio
- 2014
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In: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 51:5, s. 516-521
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Journal article (peer-reviewed)abstract
- The Birge ratio is applied in metrology to enlarge quoted uncertainties when combining inconsistent measurement results on the same measurand. We discuss the statistical model underlying such a procedure and argue that the resulting uncertainty associated with the adjusted value is underrated. We provide a simple modification of this uncertainty on the basis of an objective Bayesian inference. While the proposed uncertainty approaches that obtained by the conventional procedure for a large number n of combined measurement results, differences are significant for small n. For example, for n = 4 we get an increase of 73% in the standard uncertainty associated with the adjusted value, and for n = 10 the increase is still 13%. We derive the posterior distribution for the adjusted value in closed form, including a 95% credible interval. In addition, we show that our results do not only hold when the distribution of the measurement results is assumed to be Gaussian, but for a whole family of (elliptically contoured) location-scale distributions. We illustrate the modified Birge method by its application to data from the 2002 adjustment of the Newtonian constant of gravitation.
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| 4. |
- Johansson, Ingvar
(author)
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Metrological thinking needs the notions of parametric quantities, units and dimensions
- 2010
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In: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 47:3, s. 219-230
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Journal article (peer-reviewed)abstract
- The paper introduces a distinction between true metric and parametric quantities, units and dimensions. It claims in its first part that these distinctions shed important light both on the base quantity amount of substance and VIM's definitions of kind of quantity and quantity dimension. The second part is devoted to the unit one, and it claims that this unit must be regarded as a parametric unit, but also that it is not as needed as has been thought. The third part takes for granted that both the mole and the unit one are parametric units, and it argues that, for pedagogical reasons, the mole should be exchanged for the unit one, and the parametric quantity amount of substance be renamed as 'elementary entities'.
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| 5. |
- Jousten, K., et al.
(author)
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Final report of key comparison CCM.P-K12 for very low helium flow rates (leak rates)
- 2013
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In: Metrologia. - : IOP Publishing Ltd.. - 0026-1394 .- 1681-7575. ; 50:Suppl.
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Journal article (peer-reviewed)abstract
- Quantitative leak tests with vacuum technology have become an important tool in industry for safety and operational reasons and to meet environmental regulations. In the absence of a relevant key comparison, so far, there are no calibration measurement capabilities published in the BIPM data base. To enable national metrology institutes providing service for leak rate calibrations to apply for these entries in the data base and to ensure international equivalence in this field, key comparison CCM.P-K12 was organized. The goal of this comparison was to compare the national calibration standards and procedures for helium leak rates. Two helium permeation leak elements of 4×10−11 mol/s (L1) and 8×10−14 mol/s (L2) served as transfer standards and were measured by 11 national metrology institutes for L1 and 6 national metrology institutes for L2. Equivalence could be shown for 8 laboratories in the case of L1 and for all 6 in the case of L2. Three different evaluation methods were applied and are presented in this report, but the random effects model was accepted as most suitable in our case.
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| 6. |
- Martín, Ricardo, et al.
(author)
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Final report on supplementary comparison EURAMET.EM-S29 : Traceability of DC high voltage reference measuring systems up to 200 kV
- 2012
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In: Metrologia. - 0026-1394 .- 1681-7575. ; 49, s. 1001-
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Journal article (peer-reviewed)abstract
- The purpose of the EURAMET supplementary comparison EURAMET.EM-S29 was to compare the calibration and measurement capabilities of the participating institutes. The pilot laboratory was the Laboratorio Central Oficial de Electrotecnia (LCOE, Madrid, Spain), and the other participants were the following other six EURAMET national metrology institutes: BIM (Bulgaria), MIKES (Finland), PTB (Germany), SP (Sweden), UME (Turkey) and VSL (The Netherlands), and the COOMET national institute VNIIMS (Russia). A 200 kV DC reference measuring system provided by LCOE was used as a travelling reference measuring system (TRMS). The comparison measurements were carried out between November 2007 and April 2010. According to the technical protocol, two different types of measurements had to be made: determination of the assigned scale factor of the TRMS between 1 kV and 200 kV, positive and negative polarity, and short-term stability of the measuring systems used. For each voltage level and polarity, a comparison reference value was calculated. Compatibility of each participant with the corresponding comparison reference values and between any pair of laboratories was also obtained. Results of the comparison offered a good opportunity to check the calibration and measurement capabilities of the participants in the field of high voltage DC measurement. The reported results also demonstrate the importance of taking care in order to cancel the influence of the self-heating of the TRMS. Main text. To reach the main text of this paper, click on Final Report [http://www.bipm.org/utils/common/pdf/final_reports/EM/S29/EURAMET.EM-S29.pdf] . Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/ [http://kcdb.bipm.org/] . The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
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| 7. |
- Matthews, Clare E., et al.
(author)
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Mathematical modelling to support traceable dynamic calibration of pressure sensors
- 2014
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In: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 51:3, s. 326-338
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Journal article (peer-reviewed)abstract
- This paper focuses on the mathematical modelling required to support the development of new primary standard systems for traceable calibration of dynamic pressure sensors. We address two fundamentally different approaches to realizing primary standards, specifically the shock tube method and the drop-weight method. Focusing on the shock tube method, the paper presents first results of system identification and discusses future experimental work that is required to improve the mathematical and statistical models. We use simulations to identify differences between the shock tube and drop-weight methods, to investigate sources of uncertainty in the system identification process and to assist experimentalists in designing the required measuring systems. We demonstrate the identification method on experimental results and draw conclusions.
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| 8. |
- Pendrill, Leslie
(author)
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Using measurement uncertainty in decision-making & conformity assessment
- 2014
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In: Metrologia. - 0026-1394 .- 1681-7575. ; 51, s. S206-S218
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Journal article (peer-reviewed)abstract
- Measurements often provide an objective basis for making decisions, perhaps when assessing whether a product conforms to requirements or whether one set of measurements differs significantly from another. There is increasing appreciation of the need to account for the role of measurement uncertainty when making decisions, so that a 'fit-for-purpose' level of measurement effort can be set prior to performing a given task. Better mutual understanding between the metrologist and those ordering such tasks about the significance and limitations of the measurements when making decisions of conformance will be especially useful. Decisions of conformity are, however, currently made in many important application areas, such as when addressing the grand challenges (energy, health, etc), without a clear and harmonized basis for sharing the risks that arise from measurement uncertainty between the consumer, supplier and third parties. In reviewing, in this paper, the state of the art of the use of uncertainty evaluation in conformity assessment and decision-making, two aspects in particular—the handling of qualitative observations and of impact—are considered key to bringing more order to the present diverse rules of thumb of more or less arbitrary limits on measurement uncertainty and percentage risk in the field. (i) Decisions of conformity can be made on a more or less quantitative basis—referred in statistical acceptance sampling as by 'variable' or by 'attribute' (i.e. go/no-go decisions)—depending on the resources available or indeed whether a full quantitative judgment is needed or not. There is, therefore, an intimate relation between decision-making, relating objects to each other in terms of comparative or merely qualitative concepts, and nominal and ordinal properties. (ii) Adding measures of impact, such as the costs of incorrect decisions, can give more objective and more readily appreciated bases for decisions for all parties concerned. Such costs are associated with a variety of consequences, such as unnecessary re-manufacturing by the supplier as well as various consequences for the customer, arising from incorrect measures of quantity, poor product performance and so on.
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