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 Multicrystalline Silicon Solar Cell with 21.9 % Efficiency: Fraunhofer ISE Again Holds World Record
20.02.2017 | Fraunhofer-Institut für Solare Energiesysteme ISE

nachricht Six-legged robots faster than nature-inspired gait
17.02.2017 | Ecole Polytechnique Fédérale de Lausanne

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: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Impacts of mass coral die-off on Indian Ocean reefs revealed

21.02.2017 | Earth Sciences

Novel breast tomosynthesis technique reduces screening recall rate

21.02.2017 | Medical Engineering

Use your Voice – and Smart Homes will “LISTEN”

21.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>