[lug] THE ELECTRONIC KILOGRAM AND THE WEAKEST LINK

[J. Wayde Allen]

The following isn't Linux specific, but it does I think fit the category
of being sufficiently geeky to be of interest to some.

- Wayde
  (wallen at its.bldrdoc.gov)

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THE ELECTRONIC KILOGRAM AND 
THE WEAKEST LINK

The NIST Research ColloquiumSummer Seminars

Richard Steiner, Electronics and Electrical Engineering Laboratory
August 21, 10 a.m., Room 1-1107

In the early 1900s, measuring an ampere current standard was a fundamental but
difficult job for NBS in determining electrical standards. The advent of
quantum standards in recent decades, especially Josephson effect voltage and
quantum Hall effect resistance, changed this field of metrology. The ampere
balance became the watt balance, which now measures the ratio of mechanical
power (force times velocity in units of mass, length, and time) to electrical
power  (voltage squared divided by resistance). Using the quantum physics of
modern standards as well as their reproducibility, this experiment now measures
the Planck constant, h, in SI units. The last determination of h was completed
in 1998 at NIST with a 0.08 ppm uncertainty. In the next generation experiment,
all the applicable reference units will be quantum standards, except for mass.
As the last artifact defined as its own standard, the kilogram has become the
weakest link in the SI. A change in its mass alters the value of many physical
constants. With a new focus on monitoring the mass of the kilogram artifact, a
new watt balance with an order of magnitude lower uncertainty will become the
electronic kilogram experiment. This should bring longterm stability to mass
measurements relevant to modern metrology and lead to a redefinition of the
kilogram.