The U.S. electronics instrumentation industry, along with military and aerospace industries, maintains a position of world leadership through the development and deployment of increasingly sophisticated multi-function, high-precision, and low-maintenance instruments. U.S. laboratories and manufacturers use NIST resistance standards calibrations for cutting-edge measurements such as gene-mapping and protein synthesis, which require extremely stable temperature control. To meet the present challenging needs and in anticipation of the increasingly strict demands of advanced scientific processes, this project develops instruments and standards that enable the dissemination of a reliable unit of resistance. Many electrical measurements (e.g., at very high or low current levels) are converted to resistance measurements. Resistance standards are used to support a wide variety of measurements of impedance, temperature, strain, and power over a wide range of frequency and at very high levels of accuracy. Through this very broad customer base, the activities of this project enable U.S. industry to demonstrate and verify in a cost-effective way the accuracy of electrical measurements and the performance of high-precision instrumentation in a competitive world environment.
Maintenance of the U.S. legal ohm with the quantum Hall resistance (QHR) requires research and the pursuit of scientific breakthroughs in quantum metrology to maintain an accurate local representation of the unit, and close collaboration with other National Metrology Institutes (NMIs), including participation in international metrology comparisons to ensure international consistency of electrical measurements.
Following the CCEM-K2 Key Comparison guided by NIST, there has been a marked improvement in the quality of standards and measurements on high resistance. The world’s first Cryogenic Current Comparator (CCC) for direct scaling from the QHR up to 1 MΩ was developed at NIST in 2002. This measurement technique now has been extended to values of resistance 100 times higher, and a prototype has been used to characterize room-temperature standards and cryogenic resistance samples at 100 MΩ. While working to perfect high-ratio CCC scaling, we are pursuing the development of high-valued thin-film resistance standards for the quantum metrology triangle (QMT).
The challenge of the QMT experiment is to test the fundamental concepts underlying the Josephson voltage standard, the QHR standard, and current standards based on single-electron tunneling (SET) technologies. This experiment requires an extremely quiet high-ratio CCC, combined with SET current sources orders of magnitude larger than are presently available. Ultimately these could be used to build a source producing useful levels of quantum current. Our work on scaling to high resistances, however, represents an initial practical step toward resistance measurements using quantum current sources built up from an SET pump.
CCC systems have replaced room-temperature current comparators in many NMIs because they allow much lower uncertainty in resistance scaling. Commercialization of CCC systems has ceased for the time being because a few such systems failed to operate successfully over the long term at NMIs. CCCs, and has contracted to build a turnkey CCC system for Sandia National Laboratory (SNL). This system will duplicate a CCC used regularly at NIST for scaling and maintenance of standards between 1 W and 10 kW.
Completion of the new Advanced Metrology Laboratory (AML) has allowed the NIST resistance metrology project to operate in a superior environment with improved control of parameters such as temperature and humidity. In addition to the substantial improvement in typical laboratory conditions, this move represented a significant accomplishment, since it was completed with no disruption in the measurement services. Our most heavily used calibration systems for high-quality 1 W and 10 kW resistance standards were duplicated in the AML to facilitate the move of these calibration services. One duplicate system will now be used to study the new generation of 1 W standards built using improved resistance alloys. Improved 100 kW and 1 MW services are already in place using the updated and modified 10 kW system, allowing better measurements on newer air-type standards.
We developed high-resistance CCC measurements using a cryogenic resistor, and ways of using that type of CCC for a QMT experiment relating the Josephson effect (Josephson constant KJ) to the quantum Hall effect (von Klitzing constant RK) and the precise control of SET pump electrical charge (e). Based on Ohm’s law, this would relate the ratio of the Josephson microwave frequency fJVS and the SET pump cycle frequency fSET to the dimensionless product,
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where a represents a ratio of experimental integers, including the Josephson step number n, Hall plateau quantum number i, and number of electrons per pump cycle. From the 1998 CODATA-recommended values of fundamental constants, this dimensionless combination of fundamental constants is known to a combined relative uncertainty of ur = 7.8 * 10-8.
High-resistance standards and thin-film samples have been studied using CCCs and the NIST Active-Arm Bridge (AAB). These methods complement one another, with the CCC giving fast-response data and the AAB providing automated, long-duration data at higher voltages. Tests show great variation in absorption due to dielectric materials used to seal some high-resistance standards. The NIST thin-film cryogenic samples with resistance 100 MW are nearly free of dielectric absorption.
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Cryogenic current comparator for measurement of ~100 MW resistance samples directly against the quantum Hall resistance. |
NIST has developed high-resistance standards and Hamon-type scaling networks for calibrations up to 100 TW. The development of a number of high-resistance standards was partially funded by contracts with DoD and DOE calibration laboratories. Improved standards and automated measurement techniques at these levels allowed measurement uncertainties to be lowered by 80 % to 95 % in 2004.
Other lower-value resistor and shunt calibration uncertainties also were reduced concurrent with the distribution of Technical Note 1458, NIST and the move to the AML, in March 2004.
Over 330 calibrations were performed with approximately $360,000 income received (October 1, 2003 to September 30, 2004).
Four sets of sealed resistance standards with values 1 GW, 10 GW, 100 GW, and 1 TW were delivered to the DoD’s Army and Air Force primary standards laboratories.
A contract to build, test, and install a 100-to-1 ratio CCC for DOE’s Sandia Primary Standards laboratory was finalized in June 2004.
R. E. Elmquist, E. Hourdakis, D. G. Jarrett, and N. M. Zimmerman, “Direct resistance comparisons from the QHR to 100 Megohm using a cryogenic current comparator,” to be published in IEEE Trans. Instrum. Meas. Special Issue on Selected Papers, Conference on Precision Electromagnetic Measurements 2004.
D. G. Jarrett, R. E. Elmquist, “Settling times of high-value standard resistors,” to be published in IEEE Trans. Instrum. Meas. Special Issue on Selected Papers, Conference on Precision Electromagnetic Measurements 2004.
R. E. Elmquist, D. G. Jarrett, G. R. Jones, Jr., M. E. Kraft, S. H. Shields, and R. F. Dziuba, “NIST measurement service for dc standard resistors,” Natl. Inst. Stand. Technol. Tech. Note 1458, (December 2003).D. G. Jarrett and R. F. Dziuba, “CCEM-K2 key comparison of 10 MΩ and 1 GΩ resistance standards,” IEEE Trans. Instrum. Meas. 52, (2), pp. 474-477 (April 2003).
R. E. Elmquist, N. M. Zimmerman, and W. H. Huber, “Using a high-value resistor in triangle comparisons of electrical standards,” IEEE Trans. Instrum. Meas. 52, (2), pp. 590-593 (April 2003).
N. F. Zhang, N. Sedransk, and D. G. Jarrett, “Statistical Uncertainty Analysis of CCEM-K2 Comparison of Resistance Standards,” IEEE Trans. Instrum. Meas. 52, (2), pp. 491-494 (April 2003).
R. F. Dziuba and D. G. Jarrett, “CCEM-K2 key comparison of resistance standards at 10 MΩ and 1 GΩ,” Appendix B of Mutual Recognition Arrangement Bureau International des Poids et Mesures (BIPM) Report, also in Appendix B of the Bureau International des Poids et Mesures (BIPM) Key Comparison and Calibration Database http://www.bipm.org/pdf/final_reports/EM/K2/CCEMK2.pdf (also link from Metrologia, 39, Tech. Suppl., 01001 (2002).
D. G. Jarrett, “Analysis of a dual-balance high-resistance bridge at 10 TΩ,” IEEE Trans. Instrum. Meas. Special Issue on Selected Papers, Conference on Precision Electromagnetic Measurements 2000, 50, (2), pp. 249-254 (April 2001).
R. E. Elmquist, A.-M. Jeffery, and D. G. Jarrett, “Characterization of four-terminal-pair resistance standards: A comparison of measurements and theory,” IEEE Trans. Instrum. Meas. Special Issue on Selected Papers Conference on Precision Electromagnetic Measurements 2000, 50, (2), pp. 267-271 (April 2001).
R. E. Elmquist, M. E. Cage, Y.-H. Tang, A.-M. Jeffery, J. R. Kinard, Jr., R. F. Dziuba, N. M. Oldham, and E. R. Williams, “The ampere and electrical standards,” J. Res. Natl. Inst. Stand. Technol., 106, pp. 65-103 (January/February 2001).