Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Novel ‘Noise Thermometry’ May Help Redefine International Unit of Temperature

05.06.2008
After seven years of work, researchers at the National Institute of Standards and Technology (NIST) have built a system that relies on the “noise” of jiggling electrons as a basis for measuring temperatures with extreme precision.

The system is nearly precise enough now to help update some of the crucial underpinnings of science, including the 54-year-old definition of the Kelvin, the international unit of temperature.

NIST’s Johnson noise thermometry (JNT) system, to be described Monday, June 9, at the Conference on Precision Electromagnetic Measurements,* represents a five-fold advance in the state of the art in noise thermometry thanks to its use of a unique quantum voltage source combined with recent reductions in systematic errors and uncertainty. It is also simpler and more compact than other leading systems for measuring high temperatures, such as those based on the pressure and volume of gases.

“What’s beautiful about our JNT system is that it’s so conceptually simple,” says project leader Sam Benz. “All the measurements are electrical—they don’t require large volumes of gas and mechanical systems that change in different environmental conditions.”

As a thermometer, the JNT system will be most useful in the range from approximately 500 K (227 degrees C or 440 degrees F) to 1235 K (962 degrees C or 1763 degrees F). Its most obvious application is as a primary measurement standard (maintained at NIST and other national metrology labs for calibration of thermometers), but it also might be used directly in some industrial thermometry labs.

The recent JNT improvements are especially significant because they may contribute to a separate important measurement problem, the determination of Boltzmann’s constant. Several years from now, the international metrology community is expected to fix the value of the Boltzmann constant, used in scientific calculations to relate energy to temperature in particles. The Boltzmann constant, in turn, would then be used to redefine the Kelvin as part of an international effort to link all units to fundamental constants, a more stable and reproducible approach than traditional measurement standards based on physical objects or substances. The current Kelvin is defined in terms of the triple-point temperature of water (273.16 K, or about 0 degrees C and 32 degrees F), or the temperature and pressure at which water’s solid, liquid and vapor forms coexist in balance.

The JNT system is the only electrical approach to determining the Boltzmann constant, and is currently among the top three thermometry systems competing for the redefinition, in terms of offering the lowest uncertainties, Benz says.

The NIST system measures very small electrical noise in resistors, a common electronic component, when they are cooled to the water triple point. This "Johnson noise" is caused by the random motion of electrons and is directly proportional to temperature. The unique aspect of the system is the use of precision waveforms—electrical signals—synthesized with a superconducting alternating current (AC) voltage source whose output is based on fundamental principles of quantum mechanics, to calibrate the electronic devices measuring the noise power. This enables the system to match electrical power and thermal-noise power at the triple point of water. NIST was able to include this capability in the JNT system thanks to its recent development of the first precision instrument for synthesizing fundamentally accurate AC voltages. The quantum nature of the design assures that copies of the system will produce identical results in different laboratories, a feature that is impossible with artifact-based standards.

The most accurate measurement of the Boltzmann constant to date was performed at NIST about two decades ago using acoustic gas thermometry. The JNT system would require further improvements to be competitive with the acoustic method, but Benz thinks this is possible. A downside to the JNT system is its slow speed: It will take about one month to integrate the data to achieve the precision needed to define the Boltzmann constant, Benz says.

* S.P. Benz, H. Rogalla, D.R. White, Jifeng Qu, P.D. Dresselhaus, W.L. Tew and S.W. Nam. 2008. Improvements in the NIST Johnson Noise Thermometry System. To be presented at the Conference on Precision Electromagnetic Measurements, Broomfield, Colo., June 9.

Note for reporters: This paper is scheduled to be presented Monday, June 9, 2008, at 2:30 PM MT at session MA-2 in Ballroom A at the Omni Interlocken Resort in Broomfield, Colo.

Laura Ost | newswise
Further information:
http://www.icpem.org/2008/
http://www.nist.gov

More articles from Power and Electrical Engineering:

nachricht Large-scale battery storage system in field trial
11.12.2017 | FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbH

nachricht New test procedure for developing quick-charging lithium-ion batteries
07.12.2017 | Forschungszentrum Jülich

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

Im Focus: Virtual Reality for Bacteria

An interdisciplinary group of researchers interfaced individual bacteria with a computer to build a hybrid bio-digital circuit - Study published in Nature Communications

Scientists at the Institute of Science and Technology Austria (IST Austria) have managed to control the behavior of individual bacteria by connecting them to a...

Im Focus: A space-time sensor for light-matter interactions

Physicists in the Laboratory for Attosecond Physics (run jointly by LMU Munich and the Max Planck Institute for Quantum Optics) have developed an attosecond electron microscope that allows them to visualize the dispersion of light in time and space, and observe the motions of electrons in atoms.

The most basic of all physical interactions in nature is that between light and matter. This interaction takes place in attosecond times (i.e. billionths of a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Midwife and signpost for photons

11.12.2017 | Physics and Astronomy

How do megacities impact coastal seas? Searching for evidence in Chinese marginal seas

11.12.2017 | Earth Sciences

PhoxTroT: Optical Interconnect Technologies Revolutionized Data Centers and HPC Systems

11.12.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>