A.D. Inglis

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.

Direct determination of capacitance standards using a quadrature bridge and a pair of quantized Hall resistors

We describe measurements made using a quadrature bridge to simultaneously compare two quantum Hall resistors (QHRs) with two 10 nF capacitors at 1233 Hz. This direct approach eliminates uncertainties due to thermal and structural instabilities and to AC/DC differences of the wire resistors normally used with an AC ratio bridge as an intermediary stage.

The possible contribution of gravity measurements to the difference between the NIST and NRC watt balance results

We report on a 2012 comparison of gravity used to determine the Planck constant by the National Institute of Standards and Technology (NIST) and the National Research Council Canada (NRC) watt balances. The results provide verification of the gravity values used in recently published discrepant Planck constant determinations that play a vital role in the redefinition effort of the International System of Units (SI) and set an upper limit of 10 parts in 109 on the relative uncertainty contribution of gravity observations to future Planck constant determinations by the NIST and NRC watt balances.

A cheaper, simpler quantized Hall resistance standard

We have developed an accurate quantized Hall resistance (QHR) standard which is both cheaper and simpler to operate than most of those previously realized. In this paper, we outline the characteristics of the samples used, describe and discuss the design of the dewar and magnet system, and present field sweep data and accurate measurements carried out using a room temperature dc current comparator bridge.

Fabrication of precision quantised Hall devices

We have fabricated metrological-quality quantized Hall devices. The devices are GaAs/AlGaAs heterostructures photolithographically etched from wafers grown by molecular beam epitaxy (MBE), with evaporated AuGeNi contacts. Step 2 centers are at 7.6 and 9.7 tesla, and currents of more than 100 /spl mu/A can be carried on steps 2 and 4. The contacting has been optimized to give contact resistances of 2-3 m/spl Omega/.

CCC Bridge with digitally-controlled current sources

We have built a cryogenic current comparator (CCC) resistance bridge for the comparison of standard resistors in the range of 1 Omega-100 kOmega. The use of fully programmable current sources allows for smooth polarity reversals, regardless of the time constant of each side of the bridge. We measured a CCC transfer function of 2.25 muA middotturn/phi0 and a noise level of 54 pA middot turn/radic(Hz) at 1 Hz, with a 1/f corner of about 0.6 Hz. Two different readout schemes were implemented and compared with good agreement. We performed a few measurements to assess the accuracy of the bridge and evaluated all the significant sources of error. The total uncertainty of the bridge is estimated to be 2.6 parts in 109 between 1 Omega and 10 kOmega.

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. >

The NRC watt balance project

In 2009 NRC purchased the NPL watt balance and associated equipment and shipped it to a new purpose built laboratory in Ottawa, where the balance is being reassembled. In this paper we will describe the laboratory, give details of the rebuilding program and outline our plans and a tentative timetable for the determination of a value for Plancks constant (h).

The measurement of gravitational acceleration for the NRC watt balance

In 2009 NRC commenced construction of a new laboratory to house the NRC watt balance. We describe the procedures used and give results for the measurements of the acceleration due to gravity in the new laboratory. The data will be linked both to those laboratories participating in the Key Comparison CCM.G-K1 of 2009, and to the Canadian Gravity Standardization Network.

Direct determination of capacitance standards using a quadrature bridge and a pair of quantised Hall resistors

We describe measurements made using a quadrature bridge to simultaneously compare two quantum Hall resistors (QHRs) with two 10 nF capacitors at 1233 Hz. This direct approach eliminates uncertainties due to thermal and structural instabilities and to AC/DC differences of the wire resistors normally used with an AC ratio bridge as an intermediary stage.