Calibrations at BIPM using the present definition of the ...€¦ · CCM Workshop on the mise en...

Bureau International des Poids et Mesures

CCM Workshop on the mise en pratique of the new definition of the kilogram 21-22 November 2012, Sèvres


Calibrations at BIPM using the present definition of the kilogram

Pauline Barat, Hao Fang, Cécile Goyon

Department director: Alain Picard


Outline

Current definition

Manufacturing and cleaning of prototypes

Traceability of BIPM mass standards

Calibrations for NMIs

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Definition of the kilogram (I)

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Definition established at the 1st CGPM in 1889 :

Le kilogramme est l’unité de masse ;il est égal à la masse du prototypeinternational du kilogramme

The kilogram is the unit of mass ;it is equal to the mass of the international prototype of the kilogram

Definition interpreted by CIPM 1989 : mass of IPK just after cleaning and washingusing BIPM proceduremass deduced by extrapolation using the measured slope of 0.037 µg/day (coefficient valid no more than three months).


Definition of the kilogram (II)

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The international prototype of the kilogram with its six official copies

Four official copies from1880Two official copies added in 1939


Verifications

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Variations of about 50 µg (5 x 10–8 ) in the mass of the official copies over 100 years with respect to the IPK


Prototypes

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IPK manufactured in the 1880The first 40 prototypes were distributed in 1889. Now the BIPM has produced more than 100 prototypes.

Cylinder diameter ≈ height ≈ 39 mm

Alloy: 90% platinum / 10% iridium by mass produced by Johnson-Matthey (UK) Exception of few prototypes alloy produced by ComptoirLyon-Alemand (France).Density greater than 21.53 gcm−3.

Adjusted to a tolerance of 1 kg 1 mg.


Manufacturing of prototypes (I)

Ingot + 2 samplesDensity testρ > 21.53 gcm-3

Cutting process

Machining + weighing

Hydrostatic weighing

Density determination

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Mass dptWorkshop


Manufacturing of prototypes(II)

Machining + weighing

Polishing + weighing

Cleaning-washing

Weighing

Ethanol+Ether

m & ρ determined

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Mass dptWorkshop

1kg ± 1 mg ?

Mass evolutionduring 6 months

Yes

No


Cleaning washing of prototypes

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Cleaning Washing

Ethanol+Ether 50 minutes


Mass evolution after cleaning (I)

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50 µg

Mass evolution after a cleaning washing at each BIPM calibration


Mass evolution after cleaning (II)

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Mass evolution after a cleaning washing at each BIPM calibration

50 µg


Mass evolution without cleaning (III)

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50 µg

Mass evolution no cleaning washing since its manufacturing


Traceability of BIPM working standards to the international prototype of the kilogram

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BIPM prototypes, BIPM 1 kg working standards in platinum-iridium and in stainless steel includingalso BIPM submultiples are traceable to the international prototype of the kilogram.

International prototype of the kilogram

Its six official copies

Prototypes No 25 and No 73 reserved for special uses

Third periodic verification of national prototypes of the

kilogram(1988 – 1992)



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BIPM working standards in Pt/IrNos 9, 31, 42’,63, 77, 88, 91

and 650


kilogram(1988 – 1992)

Calibration of BIPM working standards with respect to

prototypes No. 25 and No. 73

carried out in 1991, 1998, 2001, 2005, 2008, 2009, 2011 and

2012



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BIPM working standards in Pt/IrNos 9, 31, 42’,63, 77, 88, 91

and 650

BIPM working standards in stainless steel N2, N3, J1, J2,

J3 and CH1


kilogram(1988 – 1992)

Calibration of BIPM working standards with respect to

prototypes No. 25 and No. 73

carried out in 1991, 1998, 2001, 2005, 2008, 2009, 2011 and

2012

Calibration of BIPM working standards in stainless steel with

respect toBIPM working standards in Pt/Ir

carried out several times per year


Calibration procedure (I)

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BIPM working mass standards NMI a NMI b NMI c

… … … …

2 standards

Calibrated mass

M1 M3 M5M2 M4 M6

4 positions onmass exchanger


Mass evolution of prototype (I)

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CW

10 µg

CW


Mass evolution of prototype (II)

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10 µgno CW sincemanufacturing


Comparison between Pt/Ir – Stainless steel : Corrections

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m = y + (p, t, h) ∙ V + Cg ∙ h + e

Air buoyancy correction

96 mg

Correction due to vertical gravity

gradient3 µg

m: mass difference between the two standards,y : difference in comparator reading, (p, t, h): air density (p: pressure, t: temperature, h: relative humidity),V: volume difference between the two standards,Cg: coefficient of correction due to vertical gravity gradient,h: difference in height of centre of gravity,e: undesirable magnetic force which cannot be easily corrected and so must be minimized.


Calibration uncertainty budgets

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Major uncertainty sources Standard uncertaintyCombined standard uncertainty for prototype 7 µg

Air buoyancy correction between prototype and 1 kg mass standard in stainless steel 10.6 µg

Reproducibility of BIPM working standards in stainless steel 7.0 µg

Combined standard uncertainty for 1 kg mass standard in stainless steel 15 µg

Major uncertainty sources Standard uncertainty

3rd Periodic Verification 2.3 µgStability of BIPM working standards in platinum-

iridium 6.6 µg

Combined standard uncertainty for prototype 7 µg


Mass comparators (I)

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Mettler-Toledo M-oneIPK comparison in air

Future calibrations in vacuumResolution of 0.1 µg

Six weighing positionsVacuum operation

Metrotec mass comparatorCalibration

Resolution of 0.1 µgFour weighing positions

Air operation

Comparisons Pt/Ir – Pt/IruA < 1 µg


Mass comparators (II)

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Sartorius CCL1007Avogadro Project and

Research & DevelopmentResolution of 0.1 µg

Height weighing positionsVacuum operation

Glove box

VTSvacuum transfer system

Bureau International des Poids et Mesures 23

Certificates issued during the last 10 years

0

2

4

6

8

10

12

14

16

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2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Num

ber o

f cer

tific

ates

issu

ed

Year

National Prototype Mass standard in stainless steel


Certificates

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Density and volume at 0 ºC

Thermal expansion coefficient

Mass at the date of cleaning washing

In annex mass determined after cleaning washing

In annex stability study after calibration


Conclusion: Calibrations

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Member states


Thank you for your attention !

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Calibrations at BIPM using the present definition of the ...€¦ · CCM Workshop on the mise en...

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