Metrology of the Ohm

Resistance standards traceable to NIST provide references for measurements of current at levels from 2000 A to below 1 pA and are used to support a wide variety of impedance, temperature, strain, and power measurements. This project develops the technology of quantum electrical measurements including the world’s best high resistance standards and superconducting quantum interference device (SQUID) based scaling techniques. We have maintained close working relationships with researchers in other leading national institutes and successfully completed two bilateral comparisons with the Bureau International des Poids et Measures (BIPM) and piloted five international key comparisons in the past ten years. This leadership has resulted in collaborative research to develop and deploy sophisticated multi-function, high-precision, and low-maintenance cryogenic current comparators (CCCs) of a new NIST design, which have been installed and tested  at NIST and are being installed at National Metrology Institutes (NMIs) in Argentina, Australia, and Mexico.

The Ohm Project has been a leader in providing internationally consistent resistance standards that are readily available to support the scientific and industrial foundations of the U.S. economy. Through this very broad customer base, the activities of the project enable cost-effective electrical measurements at NIST and at more than 300 U.S. sites, leading to improved performance of products and services in a competitive world environment. The resistance calibration service brings a yearly income to NIST of several hundred thousands of dollars as well as supporting over a dozen other calibration areas. Project staff provide extensive customer contact and consultation on topics including teraohmmeter measurements, the characterization processes used with resistive shunts at very high current levels, and power loading measurements to support a recent Air Force contract. Project scientists work in the U.S. and international communities, including support for comparisons at low, moderate, and high resistance levels and development of improved standards and techniques for better agreement between primary references.

The project collaborates in research on nanometer scale single-electron devices designed as biometric sensors, and two members participate in the new Quantum Conductance project that aims to develop quantum Hall resistance (QHR) devices from graphene. We pursue scientific breakthroughs to maintain accurate local representations of the unit (conventional standards) and to develop improved quantum metrology, including the recent introduction of resistive-winding cryogenic current comparators (CCCs) that enable stable SQUID operation with improved current sensitivity. This advance was combined with a two-terminal CCC bridge design that NIST developed in the 1970s, and provides the world’s only direct CCC scaling from the QHR to resistance values from 100 kΩ to 100 MΩ and above.

• Piloted SIM Key Comparisons at 1 Ω, 1 MΩ, and 1 GΩ; developed analysis to link SIM NMIs to the international community
• Automated and reported 1000 V dual-calibrator bridge measurements using fully guarded robotic actuators
• Developed CCCs for scaling up to 1 GΩ with multiple links to the QHR standard; disseminating the measurement techniques to three other NMIs
• At CPEM08, presented CCC work, SIM results, and teraohmmeter automation, and collaborated on two papers presented by other NMIs
• At NCSLI-2008, papers on power loading in 1 Ω resistors and teraohmmeter procedures