Instrumentation & Measurement Magazine 23-6 - 8

Fig. 5. NIST's relative Calibration and Measurement Capability (CMC) uncertainties from 100 μg to 50 kg using pre-2019
techniques (red) and Kibble balance and electrostatic force balances techniques within the revised SI. The red points
illustrate the left side of the 'V' profile. The green points are from the NIST electrostatic force balance (EFB). NIST-4 and
KIBB-g1 are Kibble balance implementations optimized at 1 kg and 1 g (© IEEE, 2020).

The consequence is that conventional mass scaling is still
available with essentially the same uncertainties in the revised
SI. However, other techniques are now available in the revised
SI and they can offer reduced uncertainties with respect to the
classical ''V' shaped profile (Fig. 5).
Before leaving the subject of lowering the uncertainties of
mass measurements over an extended range it is important to
note a tantalizing glimpse of what is possible. There is a class
of experiments called atomic recoil. With stabilized lasers they
create a stationary periodic electromagnetic potential and
into it place a cooled single atom. The movement of the atom
across this periodic potential can be inferred by the changing
frequency of its fluorescence. The atom's velocity is measured
before and after the atom absorbs a single photon of light. In
this way, the momentum of the photon, h/λ, is equal to the
change in momentum of the atom, m/2 (Δv)2. In the revised
SI with h fixed, this means that the mass of that atom is determined to the accuracy of measuring frequency differences.
Using this technique, the mass of a single 133Cs atom has been
determined to within a few in 109 and its magnitude is 25 orders of magnitude from 1 kg [26].

Other Impacts and Conclusions
There are other applications that the revised SI is just beginning to impact in other measurement fields and we should
mention some without details. In optical radiometry single
photon generation and detection has the promise to improve
low level traceability by orders of magnitude. Johnson noise
thermometry utilizing Josephson noise sources and non-contacting radiation thermometry promises to provide improved
accuracy and direct traceability to thermodynamic temperatures. In a novel project very high-power laser light is reflected
off a mirror and then used for welding. The momentum transfer of the light reflected off the mirror is literally weighed,
8	

providing SI traceability of the optical power while the welding is being performed [27].
These are just some of the impacts of the revised SI on measurement sector and we are certain that there will be more. It is
an exciting time for measurement science.

References
[1]	 "Resolutions Adopted," 26th Meeting of the General Conference
on Weights and Measures (CGPM), 13-16 Nov 2019, Versailles,
France. [Online]. Available: https://www.bipm.org/utils/
common/pdf/CGPM-2018/26th-CGPM-Resolutions.pdf.
[2]	 "The International System of Units," SI Brochure, 9th Ed., 2019.
[Online]. Available: https://www.bipm.org/utils/common/
pdf/si-brochure/SI-Brochure-9.pdf.
[3]	 "The Metre Convention," International Bureau of Weights and
Measures (BIPM). [Online]. Available: https://www.bipm.org/
en/worldwide-metrology/metre-convention/.
[4]	 K. Adler, The Measure of All Things: The Seven-Year Odyssey and
Hidden Error That Transformed the World. New York, NY, USA:
Simon & Schuster, 2002.
[5]	 D. B. Newell, F. Cabiati, J. Fischer et al., "The CODATA 2017
values of h, e, k, and N A for the revision of the SI," Metrologia, vol.
55, L13-16, 2018.
[6]	 P. J. Mohr, D. B. Newell, B. N. Taylor and E. Tiesinga, "Data and
analysis for the CODATA 2017 special fundamental constants
adjustment," Metrologia, vol. 55, pp. 125-146, 2018.
[7]	 P. J. Mohr, D. B. Newell and B. N. Taylor, "CODATA
recommended values of the fundamental physical constants:
2014," Rev. Mod. Phy., vol. 88, 035009-1, 2016.
[8]	 I. M. Mills, P. J. Mohr, T. J. Quinn, B. N. Taylor and E. R. Williams,
"Redefinition of the kilogram: a decision whose time has come,"
Metrologia, vol. 42, pp. 71-80, 2005.
[9]	 B. P. Kibble, "A measurement of the gyromagnetic ratio of
the proton by the strong field method," in Atomic Masses and

IEEE Instrumentation & Measurement Magazine	

September 2020


https://www.bipm.org/utils/common/pdf/CGPM-2018/26th-CGPM-Resolutions.pdf https://www.bipm.org/utils/common/pdf/CGPM-2018/26th-CGPM-Resolutions.pdf https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9.pdf https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9.pdf https://www.bipm.org/en/worldwide-metrology/metre-convention/ https://www.bipm.org/en/worldwide-metrology/metre-convention/

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