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Automatic Protocol for the Direct Comparison of Josephson Voltage Standards
Yi-Hua Tang
NCSLI Measure | Vol. 6 No. 1 (2011) | 10.1080/19315775.2011.11721548
Publisher NCSL International | Published 3/1/2011 | Pages 54-59
Abstract: In 2004, the Bureau International des Poids et Mesures (BIPM) initiated a new campaign of direct Josephson Voltage Standard (JVS) comparisons at 10 V (EM.BIPM-K10.b) using the refined BIPM protocols, Options A and B. More than
a dozen comparisons between BIPM and National Metrology Institutes (NMIs) have been carried out using the Option B protocol. They are reported in the BIPM Key Comparison Data Base (KCDB) and have played a critical role in the achievement of global
uniformity in dc voltage metrology. This paper presents an alternative automatic protocol that was recently developed to reduce the significant amount of manual operations that are required by the BIPM protocols. The successful JVS comparison between
the National Institute of Standards and Technology (NIST) and BIPM (BIPM.EM-K10.b), that was carried out in March 2009 using the BIPM Option A and B protocols, as well as the alternative automatic protocol, verified the equivalence of the two JVS
systems, including their hardware and software. The results from both participants differed by −0.8 nV with an overall standard uncertainty of 0.95 nV at 10 V or a relative standard uncertainty of 9.5 × 10−11. This comparison demonstrated that the
NIST alternative protocol achieves measurements that are in complete agreement with the measurements accomplished with the BIPM Option A and B protocols. The significance of the NIST-BIPM JVS comparison was extended to the June 2009 Sistema Interamericano
de Metrologia (SIM) regional comparison (SIM.EM.BIPM-K10.b.1) between NIST and the National Institute of Metrology, Standardization and Industrial Quality (INMETRO), Brazil, to establish a link between BIPM and INMETRO. The difference between INMETRO
and the BIPM was found to be −0.26 nV with a standard uncertainty of 1.76 nV at 10 V or a relative standard uncertainty of 1.76 × 10−10.
NCSLI Measure | Vol. 6 No. 1 (2011) | 10.1080/19315775.2011.11721550
Publisher NCSL International | Published 3/1/2011 | Pages 66-73
Abstract: The Moore M48 coordinate measuring machine (CMM) has provided the National Institute of Standards and Technology (NIST) with flexible measurement capabilities for many years. The machine's state of the art performance was further
improved following the move of the machine into the new Advanced Measurement Laboratory (AML) on the Gaithersburg, Maryland site. These improvements are particularly evident in the measurement of 1D step gauges of lengths approaching a meter. This
paper will describe the measurement process currently used for these long 1-D artifacts. The development of the data collection algorithms, data analysis techniques, and process control methods will be discussed. The impact of thermal issues, elastic
deformation resulting from probe contact, gauge fixturing, and coordinate system generation and the impact of these considerations on the measurement uncertainty budget will be presented in detail.
NCSLI Measure | Vol. 6 No. 1 (2011) | 10.1080/19315775.2011.11721549
Publisher NCSL International | Published 3/1/2011 | Pages 60-65
Abstract: VSL has designed a new line scale calibration facility that achieves a measurement uncertainty of (30 + 500 L) nm with the length L in m, for an increased measurement range of 1 m. The new facility uses a vision system that
moves over the line scale and captures images of the line scale markers while the position is measured synchronously with a laser interferometer. The measurement sequence is fully automated in order to minimize manual labor during the calibration
process, but also increases the calibration accuracy. The system was verified by measuring a platinum-iridium x-meter bar that was the Dutch meter national standard until the early 1960's. The sources of uncertainty are discussed and presented. Major
sources of uncertainty include the calibration of the vision system, the measurement repeatability, and the corrections due to the environmental conditions both for the interferometer reading and for the line scale thermal expansion. The next steps
are to validate the system by comparison to the results from other national metrology institutes; then VSL will be able to provide internationally accepted calibration services for line scales using the new facility.
NIST's High Frequency Metrology Programs: Current Capabilities and Future Directions
Ronald Ginley
NCSLI Measure | Vol. 6 No. 1 (2011) | 10.1080/19315775.2011.11721547
Publisher NCSL International | Published 3/1/2011 | Pages 48-53
Abstract: Several core areas are covered by the National Institute of Standards and Technology (NIST) microwave metrology services. These include thermal noise, power, scattering-parameters (s-parameters), field strength and antenna parameters.
The rapid change in technology and the current economic conditions have motivated us to re-examine our services and make changes where necessary. In this paper, the current state of the microwave measurement services at NIST is examined, what changes
are happening to those services are discussed, and then a glimpse of the future directions for the programs is given.
Temperature Stabilization System with Millikelvin Gradients for Air Refractometry Measurements Below the 10−8 Level
Patrick Egan, Jack Stone
NCSLI Measure | Vol. 6 No. 1 (2011) | 10.1080/19315775.2011.11721546
Publisher NCSL International | Published 3/1/2011 | Pages 40-46
Abstract: Refractometry of air is a central problem for interferometer-based dimensional measurements. Refractometry at the 10−9 level is only valid if air temperature gradients are controlled at the millikelvin (mK) level. Very precise
tests of second-generation National Institute of Standards and Technology (NIST) refractometers involve comparing two instruments (two optical cavities made from ultralow expansion glass) that are located in nominally the same environment; temperature
gradients must be kept below a few millikelvin to achieve satisfactory precision of these tests. This paper describes a thermal stabilization scheme that maintains < 1 mK thermal gradients over 100 h in a 0.5 m × 0.15 m × 0.15 m volume. The approach
uses passive (aluminum envelopes and foam insulation) and active (thermistors, foil heaters, and proportional–integral–derivative control) temperature stabilization. Thermal gradients are sensed with thermocouples and a nanovoltmeter and switch; the
reference junctions of the thermocouples being in thermal contact with a thermistor temperature standard. Indirect evidence shows that performance is better than the < 1 mK uncertainty of measuring temperature gradients, the uncertainty of which
is due to limitations of the nanovoltmeter and switch.
NCSLI Measure | Vol. 6 No. 2 (2011) | 10.1080/19315775.2011.11721557
Publisher NCSL International | Published 6/1/2011 | Pages 50-62
Abstract: Mass metrology carried out in atmospheric pressure air is suitable for most every critical application. However, there is an advantage in doing mass metrology in a vacuum environment, as it eliminates the need for air buoyancy
corrections allowing a more precise determination of true mass. In addition, the major experiments for redefining the kilogram in terms of a physical constant of nature, the watt balance and the Avogadro project, both operate in vacuum. A kilogram
that is redefined by these experiments will require making the transfer from mass in vacuum to mass in air. Therefore, understanding mass metrology in a vacuum environment is essential for doing the research necessary to maintain world-class mass
standards. In this paper, we present an introduction to the techniques and apparatus needed for vacuum mass metrology and discuss some of the work in this area being done at NIST.
Investigations on Measurement Uncertainty and Stability of Dial Gauged Force Proving Instruments
Harish Kumar, Anil Kumar
NCSLI Measure | Vol. 6 No. 2 (2011) | 10.1080/19315775.2011.11721558
Publisher NCSL International | Published 6/1/2011 | Pages 64-68
Abstract: The present paper discusses the issues related to measurement uncertainty and stability of dial gauged force proving instruments of capacities 100 kN and 1 000 kN calibrated over many years. The force proving instruments have
been calibrated using force calibrating machines based on the written standard calibration procedure. As the measurement uncertainty of the force proving instruments depends on the factors like repeatability error, zero error, resolution error, etc.,
a systematic study has been carried out. The study reveals that the uncertainty of measurement of force proving instruments has been varying appreciably and it is more for lower range. Besides this effect, the deviation from their average calibration
values has also been studied and found to be varying through the years. Hence, it may be suggested that the dial gauged force proving instruments may not have consistent behavior as force transfer standard over the years and their stability studies
results are not encouraging.
Optronic Measurement, Testing and the Need for Valid Results: Example of Infrared Measurements for Defence Countermeasures
M.J.U. Du Plooy, C.J. Willers, B. Theron, M.J. Hlakola, A.E. Mudau, F.P.J. le Roux, J.J. Calitz
NCSLI Measure | Vol. 6 No. 2 (2011) | 10.1080/19315775.2011.11721556
Publisher NCSL International | Published 6/1/2011 | Pages 42-49
Abstract: In the development of defence products and applications, measurements serve a key role when characterising and verifying the behaviour and performance of components and systems. In addition, modelling and simulation depend heavily
on measured data to achieve realistic predictions, and is furthermore dependent on measured data for validation. Researchers at the Optronic Sensor Systems (OSS) Competency Area perform field measurements in the infrared (IR) spectral band, which
serve inter alia, for the design and optimisation of IR countermeasures, such as flares. An important requirement during field measurements is a deep scientific understanding of the measurement equipment, measurement processes or protocols, the test
sample, and the effects of the environment on the measurement outcome. It is also important to understand and account for the influence of the environment on the measurement outcome. This paper briefly summarises the measurement procedure used during
infrared flare measurement in the field and the use of reference measurements used to validate the instrument status, and hence, the measurement. Reference measurement results obtained from IR thermal imagers were compared to the results obtained
using a handheld infrared thermometer in order to provide confidence in the results obtained by IR thermal imagers.
An Interlaboratory Stopwatch Comparison in the SIM Region
Michael Lombardi , Leonardo Trigo, Daniel Slomovitz ,
Theodore Reddock, Gustavo Orozco, José Luiz M. Kronenberg, Bill Hoger, Ahmed Ibrahim, Victor Masi, Walter Adad, Henry Postigo Henry Diaz, J. Mauricio Lopez-Romero, Francisco Jiménez, Oscar Fellas, Harold Sanchez, Luis Mojica, Raul Solis, Ricardo José
de Carvalho, Daniel Perez
NCSLI Measure | Vol. 6 No. 3 (2011) | 10.1080/19315775.2011.11721565
Publisher NCSL International | Published 9/1/2011 | Pages 56-62
Abstract: Stopwatches and timers are used for an almost unlimited number of applications and are among the most common devices calibrated by metrology laboratories. In large nations, stopwatch calibrations are typically handled by lower
level laboratories, such as state or private laboratories in the United States. However, in smaller nations, the national metrology institute (NMI) will often accept stopwatches for calibration against the national standard. This paper describes and
presents the results of an interlaboratory stopwatch comparison that was conducted by the NMIs of the Sistema Interamericano Metrologia (SIM) region from May 2010 through February 2011. The interlaboratory comparison involved two travelling stopwatches
and 13 NMIs. Despite a large variation in experience, calibration methods, and instrumentation, most of the participants obtained measurement results that agreed to within 1 × 106 of the pilot laboratory.
Calibration of Stopwatches by Utilizing High Speed Video Recordings and a Synchronous Counter
Cho-man Tsui , Hon-man Chan, Aaron Y.K. Yan
NCSLI Measure | Vol. 6 No. 3 (2011) | 10.1080/19315775.2011.11721566
Publisher NCSL International | Published 9/1/2011 | Pages 64-71
Abstract: A new method for the calibration of stopwatches, called video totalize method, has been developed at the Hong Kong Standards and Calibration Laboratory (SCL). The method starts with the taking of two short video clips of the
display of the stopwatch under test, together with the reading of an in-house designed synchronous counter, with the two clips separated by an interval of six to seven hours. The 10-digit synchronous counter is driven by a 1 kHz clock which is phase
locked to the cesium frequency standard of SCL. The elapsed times measured by the stopwatch and the synchronous counter are obtained by viewing the recorded video to search frame-by-frame for the instant at which the reading of the stopwatch changes.
Using this method, the measurement uncertainty is no longer constrained by the display resolution of the stopwatch, but instead is limited only by the frame rate of the video recording. Digital cameras that can record video at 420 frames per second
with usable image quality are commercially available. SCL has designed and built a synchronous counter that allows the reference time to be readfrom the recorded video with a resolution of 1 ms. The measurement uncertainty obtainable by this calibration
method is less than 2 × 10−7 for a 95 % coverage interval.
Enough Is Enough: Selecting Points for Range Calibration
Mark Kuster
NCSLI Measure | Vol. 6 No. 3 (2011) | 10.1080/19315775.2011.11721564
Publisher NCSL International | Published 9/1/2011 | Pages 40-55
Abstract: While the highest level measurement standards are frequently artifacts that provide a single reference value or a series of discrete references, measurement and test equipment encountered in the typical metrology laboratory
provides or measures quantities over a continuous range of values. Typically, the manufacturer specifies the accuracy of each range with a continuous, if not smooth, function. A specification that applies to every possible value in the range challenges
the laboratory to intelligently select an adequate, but not wasteful, number of test points at which to verify compliance to the specification. This paper investigates the reliability of the resulting calibration based on the measurement points selected,
the instrument's linearity model, and the measurement process uncertainties at each point. Applications include instruments ranging from highly linear electronic devices to non-linear physical transducers. The paper also mentions techniques to optimize
the calibration point selection.
NCSLI Measure | Vol. 6 No. 3 (2011) | 10.1080/19315775.2011.11721567
Publisher NCSL International | Published 9/1/2011 | Pages 72-77
Abstract: ‘Measurement error’2 has historically been defined in the metrology community as a difference of ‘values,’ usually as a difference between a ‘measured value’ and a ‘reference value.’ The reference value is sometimes considered
to be a ‘true value,’ which is unknowable, and so the ‘measurement error’ is then unknowable. However, in some cases the reference value is considered to be a value assigned to a measurement standard (e.g., a ‘conventional value’), which can be known.
In this case, ‘measurement error’ is regarded as being knowable and measurable (for example, the ‘error of indication of a measuring system’). The characteristic of being “measurable” requires that there be a corresponding ‘quantity’ that can be measured.
When measurement error is considered to be measurable, it must then be regarded as a ‘quantity’ (and not as a ‘quantity value’). Although the concepts of ‘quantity’ and ‘quantity value’ are related, they are distinct concepts, and from a terminological
perspective the same term (“error”) cannot be used for both concepts. This paper addresses the dilemma of how best to regard ‘measurement error’ and associated concepts: as quantity values or as quantities. This distinction has important implications
when considering the concept of ‘uncertainty of error,’ which arises when error is considered to be measurable.
A Bilateral Comparison Between NIST and INMETRO on Humidity Standards in the Dew/Frost-Point Temperature Range from −30 °C to 20 °C
Peter Huang, Julio Brionizio
NCSLI Measure | Vol. 6 No. 4 (2011) | 10.1080/19315775.2011.11721573
Publisher NCSL International | Published 12/1/2011 | Pages 34-39
Abstract: This paper presents the results of a regional metrology organization (SIM – Inter-American Metrology System) bilateral comparison of the realizations of the scale of dew/frost point temperature at the participating national
metrology institutes: National Institute of Standards and Technology (NIST, USA) and National Institute of Metrology, Standardization and Industrial Quality (INMETRO, Brazil). A total of four humidity levels in terms of dew/frost-point temperature
are used for the comparison: 20 °C, 0 °C, −10 °C and −30 °C. At each measured value, the mean and standard deviation of multiple readings of the transfer standard, which is a chilled-mirror type of dew-point hygrometer, were recorded. The results
of statistical analysis support the conclusion that the measurement data can be assumed to have the form of a normal distribution. The combined standard uncertainty ranged from approximately 0.02 °C to 0.08 °C.
Direct JVS Comparison between NIST and SNL to Support NCSLI JVS ILC 2011
Yi-Hua Tang, Harold Parks, M. Salazar, J. Novak
NCSLI Measure | Vol. 6 No. 4 (2011) | 10.1080/19315775.2011.11721574
Publisher NCSL International | Published 12/1/2011 | Pages 40-45
Abstract: The National Conference of Standard Laboratories International (NCSLI) started its 9th Josephson Voltage Standard (JVS) Interlaboratory Comparison (ILC) in March 2011. Sandia National Laboratories (SNL) is the pivot laboratory
for this comparison of JVS systems that are currently in operation at several U.S. companies and national laboratories. In order to ensure the uniformity and traceability of the representation of the volt based on the Josephson constant (1990) in
all the participating laboratories, the National Institute of Standards and Technology (NIST) DC Volt Laboratory and SNL performed a direct JVS comparison from December 6, 2010 to December 10, 2010 at SNL, Albuquerque, NM. In this JVS comparison,
the difference between the NIST Compact JVS (CJVS) and the SNL JVS was found to be −2.08 nV ± 2.88 nV at 10 V (k = 2). The large number of measurement data points enabled research investigations, such as the evaluation of the impact of the null detector's
gain error and the filter network on the comparison result. The team discovered that the polarization of the dielectric material of the SNL cryoprobe filter capacitors could affect the comparison outcome. The difference between the two JVSs was reduced
from −6.50 nV to −2.08 nV by extending the waiting period for the capacitor recovery from polarization to equilibrium. An in-situ JVS comparison between the NIST CJVS and the SNL JVS via a set of Zener transfer standards at 10 V was also carried out.
The difference was 12 nV ± 21 nV at 10 V (k = 2). This result is consistent with the results from similar past JVS ILC comparisons. The same set of Zeners will be used in the JVS ILC that is scheduled to begin in March 2011. The result of this direct
JVS comparison achieved an uncertainty level comparable to the international key comparison BIPM.EM.K10.b in the Bureau International des Poids et Mesures (BIPM) Key Comparison Data Base (KCDB). This bilateral JVS comparison has confirmed that SNL
is capable of performing its role as the pivot laboratory in the upcoming NCSLI JVS ILC. The results of the NCSLI JVS ILC will allow its participants to establish a voltage measurement link to NIST via the pivot laboratory SNL.
Platinum Resistance Thermometers: Converting Ohms to Degrees Celsius
Hans Liedberg
NCSLI Measure | Vol. 6 No. 4 (2011) | 10.1080/19315775.2011.11721577
Publisher NCSL International | Published 12/1/2011 | Pages 62-67
Abstract: Platinum resistance thermometers (PRTs) are the most common reference standards used in thermometry calibration laboratories. They are calibrated either directly in terms of resistance, producing a table of “actual temperatures”
(determined by higher-level standards, for example, standard PRTs or fixed points) and “measured resistances” of the Unit Under Test (UUT), or together with a readout (as a system) that displays the “indicated temperature” of the UUT, using one of
a number of equations to convert measured resistance to temperature. In both cases, significant errors can arise during use, if interpolation between resistance-temperature data pairs is performed using an overly simple technique, or if the conditions
of calibration and use of a (PRT + readout) system are not precisely defined and carefully adhered to. This paper discusses several methods of converting resistance to temperature, the drawbacks of each method, and techniques to reduce the possibility
of error when using a calibrated PRT.
The New International System of Units: The Role of the Committee on Data for Science and Technology (CODATA)
B.N. Taylor, P.J. Mohr, David B. Newell
NCSLI Measure | Vol. 6 No. 4 (2011) | 10.1080/19315775.2011.11721576
Publisher NCSL International | Published 12/1/2011 | Pages 54-61
Abstract: The mission of the Committee on Data for Science and Technology (CODATA) of the International Council for Science is to strengthen international science for the benefit of society by promoting improved scientific and technical
data management and use. One of their most visible outputs comes from the Task Group on Fundamental Constants (TGFC), which periodically performs a comprehensive least-squares adjustment of the values of the constants and produces the well-known and
widely cited publication entitled “CODATA recommended values of the fundamental physical constants: year” (freely available at http://physics.nist.gov/cuu/constants). When the proposal to change the International System of Units (SI) by redefining
the kilogram, ampere, kelvin, and mole in terms of fixed values of the Planck constant h, elementary charge e, Boltzmann constant k, and Avogadro constant NA, respectively, is implemented in the near future, it will be the responsibility of the TGFC
to provide these values. In this presentation, the least-squares adjustment procedure will be outlined and illustrated with reference to current state-of-the-art measurements in several physical disciplines.
Trace-Humidity Calibration and Testing Services at the National Institute of Standards and Technology
Wyatt W. Miller, G.E. Scace
NCSLI Measure | Vol. 6 No. 4 (2011) | 10.1080/19315775.2011.11721578
Publisher NCSL International | Published 12/1/2011 | Pages 68-76
Abstract: The National Institute of Standards and Technology (NIST) provides low-humidity calibration and testing services for hygrometers and humidity generators over a humidity range between 3 nanomole per mole (nmol/mol, parts per
billion, or ppb) of water vapor in nitrogen and 3 000 micromole per mole (μmol/mol, parts per million, or ppm). Hygrometer calibrations are typically performed by subjecting the hygrometer to various H2O/N2 mixtures produced by the NIST Low Frost-Point
Generator (LFPG), and comparing the water vapor concentration reported by the device under test to that of the LFPG. Humidity generator calibrations are typically performed by adjusting both the LFPG and the humidity generator under test to produce
nominally the same concentration of H2O in N2, then measuring the difference in water vapor concentration through sequential measurements taken with a sensitive hygrometer. In the case of permeation-tube humidity generators, NIST offers either complete
generator calibration, or calibration of water permeation-tubes. In addition to calibration services, NIST provides individually-customized testing services in which the LFPG routinely provides low-uncertainty H2O/N2 mixtures for prototype testing,
development of new measurement technologies, and for scientific experiments. In this paper we discuss the trace-humidity calibration and testing services available at NIST. The LFPG, and its performance are presented. Examples are provided of how
the calibration and testing of hygrometers and humidity generators are performed. We supply details of how to obtain NIST calibration and testing services.
U.S. Air Force Metrology and Calibration Program's NextGen Calibration Automation System: Updates and Lessons Learned
Alan Gibson
NCSLI Measure | Vol. 6 No. 4 (2011) | 10.1080/19315775.2011.11721575
Publisher NCSL International | Published 12/1/2011 | Pages 46-53
Abstract: The core of the Air Force Metrology and Calibration Program's NextGen Automated Calibration Software are three defined layers that are the backbone of the system: (1) Sequencer Layer which handles equipment configuration, graphical
user interface, and abstracts test logic into a readable XML standard; (2) Measurement Module Layer which runs the calibration technique, timing and the taking of measurement data independent to whatever specific instruments are being used; and (3)
Communication Layer which controls the instruments, communication buses and equipment substitution. All three layers have been updated over the years that NextGen has been in use; however, changes in one layer have had little to no impact on the remaining
two. The resulting effect of this is that updates to one area can be applied at any time without affecting the work currently in progress on another. Updates to the Sequencer Layer have included multiple measurements per data table, consolidation
of methods, and handling of instrument options. Some Measurement Module Layer changes have included multiple connection diagrams, module configurations, and a developer/engineer communication technique dubbed “Runnable Specifications.” Finally, the
Communication Layer has been enhanced by decentralizing communicator objects, creating a manual communicator, and adding XML based instrument command files. This paper describes the various updates that have been made to overcome obstacles, implement
new ideas, and to save development and maintenance time.
