Yi-hua Tang

NIST 10 V Programmable Josephson Voltage Standard System

The National Institute of Standards and Technology has developed and implemented a new programmable Josephson voltage standard (PJVS) that operates at 10 V. This next-generation system is optimized for both dc metrology and stepwise-approximated ac voltage measurements for frequencies up to a few hundreds of hertz. The nonhysteretic Josephson junctions produce intrinsically stable voltages and are designed to operate in the 18-20 GHz frequency range. The most recent 10 V PJVS circuits have total output current ranges greater than 1 mA.

Thermal voltage converter calibrations using a quantum ac standard

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.

Evaluating the uncertainty of Josephson voltage standards

A general method is proposed to evaluate the uncertainty of Josephson voltage standard measurements exclusive of the uncertainty contributed by the device under test. The method is based on a statistical evaluation of the results of measurements of a short circuit under conditions that exactly duplicate the procedure used for normal calibrations. It gives a rigorous Type A evaluation of many uncertainty components that have typically been considered Type B uncertainties and often assigned worst-case values. Uncertainty components for frequency and leakage are not detected by short-circuit measurements and are separately evaluated. The method is applied to the results of an interlaboratory comparison and used to generate a statement of equivalence.

A two-way Josephson voltage standard comparison between NIST and NRC

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 NRCs 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 1010.

A 10 V programmable Josephson voltage standard and its applications for voltage metrology

The concept of a programmable Josephson voltage standard (PJVS) was first proposed in 1997. Since then a significant amount of research and development work has been devoted to the fabrication of the programmable Josephson junction array and its deployment in a voltage standard system. This paper reports the recent development of a 10 V PJVS system at the National Institute of Standards and Technology (NIST) and its voltage metrology applications. The superior stability of the voltage step of the new 10 V PJVS enables it to perform the same tasks as the conventional Josephson voltage standard (JVS) that uses hysteretic voltage steps and to improve the efficiency and effectiveness of a JVS direct comparison. For the first time, a comparison between a conventional JVS and the NIST 10 V PJVS was performed in order to verify the performance of the NIST 10 V PJVS. The mean difference between the two systems at 10 V was found to be −0.49 nV with a combined standard uncertainty of 1.32 nV (k = 1) or a relative combined standard uncertainty of 1.32 parts in 1010. Automatic comparisons between the 10 V PJVS and a 2.5 V PJVS at 1.018 V were performed to monitor the long term accuracy and stability of the 2.5 V PJVS and to support the NIST electronic kilogram experiment. By matching the voltages of the two PJVS systems during a comparison, the type B uncertainty can be minimized to a negligible level. The difference between the two PJVS at 1.018 V was found to be −0.38 nV with a combined standard uncertainty of 0.68 nV (k = 1) or a relative combined standard uncertainty of 6.7 parts in 1010. Issues encountered during the PJVS comparison and potential challenges for 10 V applications are also discussed.

Correction of Systematic Errors Due to the Voltage Leads in an AC Josephson Voltage Standard

NIST recently reported the first application of a quantum AC Josephson voltage standard (ACJVS) for calibration of thermal transfer standards in the 1 kHz to 10 kHz frequency range. This paper describes preliminary work on extending its frequency calibration range up to 100 kHz by correcting systematic errors due to voltage leads.

The Seventh Intercomparison of Josephson Voltage Standards in North America

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

The Ampere and Electrical Standards.

This paper describes some of the major contributions to metrology and physics made by the NIST Electricity Division, which has existed since 1901. It was one of the six original divisions of the National Bureau of Standards. The Electricity Division provides dc and low-frequency calibrations for industrial, scientific, and research organizations, and conducts research on topics related to electrical metrology and fundamental constants. The early work of the Electricity Division staff included the development of precision standards, such as Rosa and Thomas standard resistors and the ac-dc thermal converter. Research contributions helped define the early international system of measurement units and bring about the transition to absolute units based on fundamental principles and physical and dimensional measurements. NIST research has helped to develop and refine electrical standards using the quantum Hall effect and the Josephson effect, which are both based on quantum physics. Four projects covering a number of voltage and impedance measurements are described in detail. Several other areas of current research at NIST are described, including the use of the Internet for international compatibility in metrology, determination of the fine-structure and Planck constants, and construction of the electronic kilogram.

Complete characterization of Zener standards at 10 V for measurement assurance program (MAP)

A complete characterization of Zener standards for temperature, pressure, and humidity is being performed to improve the uncertainty of a MAP that uses 10 V Zeners as travelling standards. The procedure and equipment used for this work are briefly described. We will report results of evaluating our available pool of Zener standards.

A 10 V Josephson Voltage Standard Comparison Between NIST and INMETRO as a Link to BIPM

This paper describes a 10 V Josephson Voltage Standard (JVS) direct comparison between the National Institute of Standards and Technology (NIST) and the Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO) using automatic data acquisition. The results were in agreement to within 1.1 nV and the mean difference between the two JVSs at 10 V is 0.54 nV with a pooled combined standard uncertainty of 1.48 nV. Considering a recent JVS comparison between NIST and the Bureau International des Poids et Mesures (BIPM), the difference between INMETRO and the BIPM thus was found to be -0.26 nV with a standard uncertainty of 1.76 nV. INMETRO JVS improvements since the 2006 INMETRO-BIPM comparison are also described.