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ABSTRACT: Stochastic serial correlations are often ignored in the statistical uncertainty (Type A) analysis of measurement values. For repeated measurements, the standard deviation of the mean is often used to specify Type-A uncertainty, but it is frequently underestimated by assuming that it is given by the standard deviation divided by the square root of the number of measurements. Methods of time-series analysis such as the Allan variance (Avar) formalism give realistic estimates of Type-A uncertainty, but they require equal time intervals between successive measurements. This requirement is difficult to satisfy in comparisons of Josephson voltage standards (JVSs) because of the instability of the voltage steps and the small number of repeated measurements. A JVS comparison was made using a completely automatic compact JVS. The time intervals were uneven; thus, we studied the effect of their irregularity on the Avar by simulating data having the same noise model and uneven time intervals as the measured data. We found that, for this JVS comparison, the Avar is only slightly affected by uneven intervals. The noise was found to be a mixture of white and 1/ f noise. The latter limits the Allan deviation to 0.64 nV after 14.3 h of measurement. The method of simulating data this way should be applicable to other complex measurement situations.
IEEE Transactions on Instrumentation and Measurement 08/2011; · 1.21 Impact Factor
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Yi-Hua Tang
IEEE T. Instrumentation and Measurement. 01/2011; 60:2404-2408.
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IEEE T. Instrumentation and Measurement. 01/2011; 60:2248-2254.
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IEEE T. Instrumentation and Measurement. 01/2011; 60:2482-2488.
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ABSTRACT: A comparison of the 10 V Josephson array voltage standard of the Bureau International des Poids et Mesures (BIPM) was made with that of the National Institute of Standards and Technology (NIST), USA, in March 2009. For this exercise, three different measurement methods were carried out: the two different options of the BIPM.EM-K10.b comparison protocol as well as the measurement protocol applied by NIST. The results of both participants are in very good agreement and the overall relative standard uncertainty is 9.5 parts in 1011. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
Metrologia 09/2009; 46(1A):01010. · 1.75 Impact Factor
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ABSTRACT: A two-way Josephson voltage standard (JVS) direct comparison between the National Institute of Standards and Technology (NIST) and the National Research Council (NRC) has been conducted. The process consists of two comparisons: first, using the NRC JVS with the NRC's measuring system (hardware and software) to measure the 10 V provided by the NIST JVS and then using the NIST JVS measuring system to measure the 10 V provided by the NRC JVS. The results of the two comparisons are in agreement to within 0.7 nV, and their mean indicates that the difference between the two JVSs at 10 V is -0.28 nV, with a pooled combined uncertainty of 2.07 nV ( k = 2) or a relative uncertainty of 2.1 parts in 10<sup>10</sup>.
IEEE Transactions on Instrumentation and Measurement 05/2009; · 1.21 Impact Factor
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IEEE T. Instrumentation and Measurement. 01/2009; 58:821-826.
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IEEE T. Instrumentation and Measurement. 01/2009; 58:749-750.
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IEEE T. Instrumentation and Measurement. 01/2009; 58:853-858.
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ABSTRACT: We report on the first-ever use of a quantum ac source to calibrate a thermal transfer standard as part of the NIST calibration service for such devices, with reductions in calibration uncertainty of as much as an order of magnitude over traditional ac–dc transfer methods. We briefly describe the basic quantum ac calibration system, its operation and measurement results. An analysis of the uncertainties for the measurements is presented and plans for further development are described.
Metrologia 04/2008; 45(3):275. · 1.75 Impact Factor
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ABSTRACT: To achieve a balance between high performance and energy efficiency, embedded systems often use heterogeneous multiprocessor platforms which tuned for a well defined application domain. Meanwhile FPGA is known for providing designers with several benefits in system design. One most important is high programmability and low risks. In this paper we demonstrate the design of an FPGA-based heterogeneous multiprocessor system integrating 4 Nios II soft cores and 1 ARM core. ARM core is the central controller of the whole system, and 4 Nios II cores are served as slaves, which are commanded by ARM core and responsible for processing regular and quantity data. ARM core and Nios II cores cooperate and work in parallel to accomplish each task. FPGA utilization of current implementation is 13% requiring 19,593 ALUTs on Altera Stratix II EP2S180.
ASIC, 2007. ASICON '07. 7th International Conference on; 11/2007
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ABSTRACT: The seventh interlaboratory comparison of Josephson voltage standards (JVS) at 10 V, sponsored by the National Conference of Standard Laboratories International, took place from April to October 2005 with 15 participating laboratories. A traveling JVS system of the National Institute of Standards and Technology was used to make five comparisons with the subpivot laboratories. This paper describes the protocol used for the JVS intercomparison and the improvements achieved by the use of the transportable JVS
IEEE Transactions on Instrumentation and Measurement 05/2007; · 1.21 Impact Factor
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ABSTRACT: In order to improve the National Institute of Stan-dards and Technology (NIST) low-voltage calibration service for thermal-voltage converters, we have constructed an ac-Josephson-voltage-standard (ACJVS) system that can synthesize accurate rms voltages of up to 100 mV. Using this system, we synthesized dc voltages and audio-frequency sine waves in order to measure ac–dc differences on the 22 mV and 220 mV ranges of a commer-cial thermal transfer standard. By modifying the output resistance of the low-pass-filtered transmission line, we were able to extend our measurement frequency from a few kilohertz up to 100 kHz. Our ACJVS measurements agree with the uncertainty budget of ac–dc difference calibrations made of this transfer standard by use of conventional techniques. We also show the progress toward extending the output to 200 mV using new Josephson circuits.
IEEE Transactions on Instrumentation and Measurement 01/2007; 56. · 1.21 Impact Factor
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IEEE T. Instrumentation and Measurement. 01/2007; 56:605-609.
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ABSTRACT: The increasing system resources available on field-programmable gate arrays (FPGA) enable the integration of complex system on one programmable chip. This paper focuses on the design and implementation of a hierarchy-bus based multi-processor system-on-chip (MPSoC) integrating 4 ARM processors on FPGA. Experimental results had been obtained running at 60MHz with total area requiring 34% adaptive look-up tables (ALUTs) of Altera Stratix II EP2S180 and a maxim performance speedup of 3.2
Solid-State and Integrated Circuit Technology, 2006. ICSICT '06. 8th International Conference on; 02/2006
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ABSTRACT: We have investigated noise in measurements of the 10 V outputs of electronic voltage standards based on Zener diode references (Zeners). Zener outputs were compared to NIST Josephson standards using a digital voltmeter (DVM) to measure voltage differences. Because of the presence of serially correlated noise, the data were analyzed by calculating estimated Allan variances which were then used to determine the parameters of a power law model including white and 1/f noise. In many cases, the modeled Allan variances agree well with the estimated values over a wide range of sampling times. In all, we have estimated the 1/f noise floor for 25 Zeners of three types. We examined the impact on noise measurements of changes of the range of the DVM and of quantization of the recorded voltages by the DVM. We conclude that there is strong evidence of the presence of a high level of white noise in Zeners.
IEEE Transactions on Instrumentation and Measurement 05/2005; · 1.21 Impact Factor
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ABSTRACT: The 10 V Josephson voltage standard (JVS) systems of the National Institute of Standards and Technology (NIST) and the Sandia National Laboratories (SNL) were compared by two different methods used simultaneously. The first method uses the well-established technique of the NIST's Measurement Assurance Program (MAP) in which Zener-diode electronic voltage standards (often called Zener voltage standards) are used as traveling standards. The second method, reported here for the first time, used a recently developed portable JVS as the traveling standard. This method provides a thorough verification of a JVS system including all the components of hardware and software as they are used normally to calibrate a secondary voltage standard. The uncertainty of the second method was more than an order of magnitude smaller and provided a way to evaluate the uncertainty associated with the predictability of Zeners when used as traveling standards.
IEEE Transactions on Instrumentation and Measurement 03/2005; · 1.21 Impact Factor
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IEEE T. Instrumentation and Measurement. 01/2005; 54:567-570.
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IEEE T. Instrumentation and Measurement. 01/2005; 54:398-403.
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ABSTRACT: Two Josephson voltage standard (JVS) systems operated at the
National Institute of Standards and Technology (NIST) and Lockheed
Martin Astronautics (LMA) were compared by using four traveling Zener
standards. A Measurement Assurance Program (MAP) protocol was adopted
for the comparison. The Zener data were first corrected based on their
pressure coefficients to compensate for the pressure difference due to
the lab elevations and local meteorological conditions. The
Welch-Satterthwaite formula and effective degrees of freedom (DOF) were
then used to calculate the expanded uncertainty. The mean difference
between the measurements of the two laboratories was found to be 0.059
μV with an expanded uncertainty of ±0.189 μV at the 95%
confidence level
IEEE Transactions on Instrumentation and Measurement 05/2001; · 1.21 Impact Factor
