“for all time, for all people”

1

• In 2018, the CGPM is expected to vote on

a proposa

revise the International System of Units (SI).

mol

K

s

m

cd

A

kg

1: attributed to Charles‐Marie de La Con

Current SI spanned by

7 base units. Revised SI spanned by

7 defining con
A long time in the making 1990

Some of the electrical units (V,

Ω) split off from the SI due to advances in quantum metrology that are incompatible with an SI that has

its roots in 19th century mechanics. Starting in 1990 electrical measurements are

reported in conventional units.

1991B.N. Taylor recognizes that the

watt balance can be used to

realize the kilogram from fundamental constants.

2005Group of five (Mills, Mohr,

Quinn, Taylor, Williams) publishes Redefinition of the kilogram: a decision whose time has come

2005The Consultative Committee for

Mass and Related

Quantities(CCM) formulates conditions for a redefinition of

the kilogram2013The Consultative Committee forUnits (CCU) and CCM produce a roadmap.
What will change?

• No significant change for s, m, cd.

• The revised SI affects the kg, A, K, mol.

• These SI units will remain contiguous through th

revision.

• The electrical measurements will again be report

within the SI. This will cause a small shift (relativ

of 10‐7) in the electrical units.

• The realization of the units can be accessed

anywhere (Before, e.g., the kilogram was only

accessible at BIPM) through multiple paths.
The kilogram

• Artefact ba• Only acces• Only acces

(3 x in 100 

• Only at on

From

Kibble (watt)

balance

X‐ray Crystal

Density Method

• Definit

• Scalabl• Realiza

formed 

To

The kilogram, symbol kg, is the SI unit of

mass. It is defined by taking the fixednumerical value of the Planck constant h

to be 6.626 070 040 ×10–34 when

expressed in the unit J s, which is equal to

kg m2 s –1 , where the metre and the

second are defined in terms of c and ∆νCs.

The kilogram is the unit of mass; it is equal

to the mass of the international prototype

of the kilogram.
NIST’s new value for the Planck constant ‐‐ from design to firs

• current relative uncertainty (1‐sigma): 34 x 10‐9

• projected rel. uncertainty by June 2017: 20 x 10‐9

December 2013 August 2014

Source Uncertainty (10‐9)

Statistical 24.9Magnetic field 15.4

Electrical 10.9Alignment 6.5Mass metrology 6.3Mathematical 5.0Balance mechanics 5.0

Local acceleration, g 4.4Velocity 1.7Total relativeuncertainty

33.6

August 201

May 2011

March 2016

݄ ൌ 6.626	069	83ሺ22ሻ 	ൈ 10ିଷସ	Js
Vacuum Balance

Surface and Volume Artifacts

Characterize sorption properties and air density for

measurement of mass in vacuum and mass in air

Volume

Artifacts

Surface

Artifacts

Vacuum and Air St

Artifact Pool

Dissemination from an en

of Pt‐Ir and SS artifac

• Vacuum chamber pressure ~10‐5 

• Monitor pressure and gas compos

• Load‐lock to insert and remove ar

• Constant flow of filtered r

• Monitor temperature, pre

• Load‐lock to insert and rem

Vacuum

Air

MISE EN PRATIQUE

For the Realization and Dissemination of the Redefined Kilogram

Patrick J. Abbott, Edward Mulhern, Eric Benck, Zeina Kubarych

Traceability and Dissemination

Vacuum, air artifacts

Magnetic

Levitation

Transfer

Current System

New SI kg Watt Balance

(Vacuum)

Primary 1kg Mass

(Vacuum)

Secondary 1kg Mass

(Vacuum)

BIPM IPK

(Air)

US National Standard (Air) Secondary 1kg Mass

(Air)

Disseminate

New SI kg

Disseminatio

Vacuum‐to‐Air Tran

Direct comparison of known mas

unknown mass in air using magne

Realization

Watt Balance

Realization of the kilogram in vacuum

through a fixed Planck constant

Mass

Transport

Vehicle

(MTV)

4nwnvfwfv

m ൌ

 g 

Direct traceability to SI

Vacuum artifacts

Monitor Watt Balance stability

Vacuum artifacts
From Watt Balance to Magnetic Suspension Mass Comparator (MSMC)

(Once h is fixed in 2018)

Problems with present method

• Both WB and MSMC vacuum chambers must be vented, exposing the instruments to air and te

• Atmospheric contaminants adsorb onto the clean surface of the mass; measurable changes

Advantages with In‐Vacuum method• No venting required for either chamber (reduce down time)

• Removal of temperature shock on magnets due to venting

• Riddance of surface sorption corrections and sources of uncertainty
Installed load lock for mass

transfer in vacuum
Operation of the In‐Vacuum Mass Transfer System from the WB to MSMC

Watt Balance Start Point Magnetic Suspension Mas
The Ampere

From

• Definition ba

• Can count ele

e.g., SET cha

O

• Quantum ele

voltage and r

are an SI uni

To

The ampere is that constant current

which, if maintained in two straight

parallel conductors of infinite length,

of negligible circular cross section, and

placed

1 meter apart in vacuum, would

produce between these conductors

a

force equal to

2

x 10‐7 newton per

meter of length.

The ampere, symbol A, is the SI unit of

electric current. It is defined by taking

the fixed numerical value of theelementary charge

e to be 1.602 176

620

8 ×10–19 when expressed in the unit

C, which is equal to

A s, where the

second is defined in terms of ∆νCs.

• Impossible to r

of infinite lengt

so definition is

• Since 1990 elec

outside the SI

• Conventional e

quantum stand

resistance with 
The Ampere at NIST by counti

• Make devices to shuttle one electron at a

time at a high frequency using physics ofCoulomb blockade (i.e., charge pump).

݂݊݁ ൌ ݐ݀ܳ݀ ൌ ܫ

Electrons shuttling through a Coulomb

blockade device made at NIST

island

Modulate this gate fast

• Need lots of electrons t

current, so need many concept above

• An historic problem is t

gated pumps aren’t as 

• NIST is developing an a

solve this problem
The Ampere at NIST by V/R

• Making SI voltage available through

convenient instruments

23456789

0.00.20.40.6

 1.7 K 3 K 2.8 K 5.1 K

Hall resistance variation ()

B (T)

n1n2

• Making SI ohm available through new

devices based on graphene

NIST has developed novel techniques to grow graphene 

process the material into high current QHR devices. The 

compatible with our existing highly customized measure

infrastructure, but can also be used directly with comme

room temperature bridge systems, potentially revolution

accessibility of this basic electrical standard.
The Kelvin

From

• Definition is 

Boltzman con

• Quantum no

absolute stanfor chip‐base

sensors

• Triple point c

convenient re

• Precision lim

imagination 

ToThe kelvin, unit of thermodynamic temperature,

is the fraction 1/273.16 of the thermodynamic

temperature of the triple point of water.The kelvin, symbol K, is the SI unit of

thermodynamic temperature. It is defined

by taking the fixed numerical value of the

Boltzmann constant k to be 1.380 648 52

×10–23 when expressed in the unit J K–1 ,

which is equal to kg m2 s ‐2 K‐1 , where the

kilogram, metre and second are defined in

terms of h, c and ∆νCs.

• Intrinsic stand

• Requires care

environmenta

• Precision is lim

Triplepoint cell

Josephson voltage

based Johnson noisethermometer
The Kelvin at NIST

A

B

Si3N4 nanobeam optomechanical crystal

m

kBT

B

A





2

correlation

New photonic sensors New approaches based on optomechanics

Improved J
Redefinition of the Kg: What’s up?

• We are on schedule for the CIPM to ratify a redefinition in 2018!

• December 2013, International Prototype Kilogram (IPK) brought out

for first time in 25 years: Extraordinary Calibrations (Metrologia,

March 2015)

• Result: BIPM mass scale found to be

.037 mg too high relative to IPK (37 ppb)

• This largely cancels the .045 mg shift

NIST accepted in 2010

• All active Planck groups harmonized their mass to the Extraordinary

Comparison in 2015

• NIST, PTB, NMIJ, and LNE reported new Planck values in 2016

• Agreement of Planck’s constant determinations is now sufficient to

support redefinition (3 values within 50 ppb, 2 values below 20 ppb)

• Pilot study of the new kilogram is underway. BIPM is comparing

artifacts from NIST, PTB, NMIJ and LNE realized directly from Kibble

balances or X‐ray crystal density method. Results to be announced

early 2017.

Le Grand K 
Formation of CODATA

• 1966 –ICSU establishes the Committee 

on Data for Science and Technology (CODATA)

• To strengthen international science for the benefit 

of society by promoting improved scientific and technical data management and use

icsu

codata.org

• 1969 CODATA establishes the T

Group on Fundamental Consta

– To periodically provide the scientific and 

technological communities with a self-cset of internationally recommended valubasic constants and conversion factors physics and chemistry based on all of trelevant data available at a given point 
Near future: on the road to redefin
Critical Closing Date for Data

1 July 2017Closing date for data for special CODATA constants

adjustment to determine exact values of h, e, k, and

NA for 2018 revised SI (International System of

Units).

BY this date data must be published or

available in a preprint accepted for

publication.
Critical Dates

31 December 2018Closing date for data for first CODATA adjustment

of the physical constants in the new SI

20 May 20192019 World Metrology Day – Proposed date of

implementation of new SI
The last Planck must be in place July 2017

• The roadmap to redefinition goes through a final determination of the Planck

constant

• Closing date for new data that will contribute to the CODATA special adjustment

that will determine the exact value of the Defining Constants is 7/1/2017

• NIST is aiming to contribute a value with uncertainty below 20 ppb

• How will we get there?
Where does the uncertainty

in NIST’s value come from?

Source Uncertainty (10‐9)

Statistical 24.9Magnetic field 15.4Electrical 10.9Alignment 6.5Mass metrology 6.3

Mathematical 5.0Balance mechanics 5.0

Local acceleration, g 4.4Velocity 1.7Total relativeuncertainty

33.6

Dominated by the Bl calibration in the

velocity mode due to thermal drift and

insufficient cancellation. Load lock will

reduce drift. Have ideas to mechanically

improve the IFOs. Realistic goal: 8 x 10‐9.

Is limited by how well we can determine

the quadratic effect of the current on

the magnetic field, i.e., weighing at

different mass values.We hope to get this down to 10 x 10‐9.

It should be possible to get a combined

relative uncertainty of 20 x 10‐9.

Dominated by time dependentleakage, which needs further

investigation. Realistic target: 6 x 10‐9.
Final Steps – Education and Communication

• Full analysis completed on the impact on all NIST calibration services

and published

• NIST participation in international education and publicity efforts

• NIST participation in final development of mise en pratiques

• Multiple presentations on the status and anticipated impact

• Finally, developing materials for direct communication with

customers
Questions?