Barry M. Wood

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.

Improved AC quantized Hall measurements

AC quantized Hall resistance (QHR) measurements have been performed with an improved probe and sample mounting system. We describe investigations of the structure of the R/sub H/ plateau for a range of sample currents and temperatures, and for different wiring configurations. We have observed R/sub xx/ minima smaller than 0.02/spl times/10/sup -6/ of R/sub H/, an order of magnitude smaller than most published values.

Interlaboratory comparison at 10 V DC

An interlaboratory comparison at 10 V DC has been made among 16 national, industrial, and military standards laboratories in North America. The comparison used a set of four traveling Zener dc reference standards. A pivot laboratory made measurements at the beginning, at the end, and at four other times during the comparison. The measured differences and their uncertainties are reported and used to demonstrate equivalence between each participant and the pivot, and between each participant and the National Institute of Standards and Technology (NIST). All of the differences fall within two parts in 10/sup 8/.

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 Canadian realization of a quantized Hall resistance standard

A cryogenic-current-comparator-based resistance measurement system in use at the National Research Council of Canada to maintain a reference of resistance is described. Results of maintenance activities since 1990 and results of comparisons of the ratio equivalence of steps two, three, four, and six at a precision of a few parts in 10/sup 8/ are presented. >

Linear frequency dependence in AC resistance measurement

The frequency dependence of AC resistors as well as the AC quantum Hall resistance shows sometimes unexpected linear terms of the order of 1/spl middot/10/sup -7/ kHz/sup -1/. Three reasons for measuring linear terms are identified as systematic effects of the coaxial bridge and the compared resistors.

Comparison of the quantized Hall resistance and ohm NRC

A report is given of the progress towards the establishment of a quantized Hall resistance (QHR) measurement system suitable for maintaining the NRC (National Research Center of Canada) representation of the ohm. A system using a cryogenic current comparator bridge is described and compared to the previously reported 15 T, 20-mK potentiometric system. General problems concerning the use of the quantized Hall resistance to realize a representation of the ohm are discussed. >

Quantifying demonstrated equivalence

Recent debates about measurement equivalence would have been simplified by a satisfactory quantification of equivalence. We present a rigorous, simple method of using measurement comparisons to quantify equivalence statements in one parameter. It is able to treat all aspects of the ISO Guide to the Expression of Uncertainty in Measurement as they apply to measurement comparisons. We compare this method to the common usage of the normalized error.

Adaptive current sources and feedback applied to the cryogenic current comparator

We present a novel current source for the cryogenic current comparator resistance bridge which is adaptable to many coil, resistance and filtering configurations. To achieve optimum performance of the system both current feedback from the SQUID and feedback from the voltage detector are examined and incorporated into the design. The properties of the new design are improved flux tracking, leakage, and flexibility without comprising the self checking capability and accuracy. The system has been used at the NRC over the resistance range of 1 /spl Omega/ to 1 M/spl Omega/. >

Quantum Hall measurements from 4 K to 20 mK

We report on precision measurements of the quantum Hall resistance (QHR) in the temperature range of 20 mK to 4 K. These include intercomparisons of the ohm maintained at the National Research Council (OHM NRC) and the International System ohm (OHM SI) and the QHR. The effects of nonzero Rxx minima, sample inhomogeneity, nonohmic contacts, and dissipation are summarized.