Calibrations at BIPM using the present definition of the kilogram

Transcription

1 CCM Workshop on the mise en pratique of the new definition of the kilogram November 2012, Sèvres Calibrations at BIPM using the present definition of the kilogram Pauline Barat, Hao Fang, Cécile Goyon Department director: Alain Picard

2 Outline Current definition Manufacturing and cleaning of prototypes Traceability of BIPM mass standards Calibrations for NMIs 2

3 Definition of the kilogram (I) Definition established at the 1st CGPM in 1889 : Le kilogramme est l unité de masse ; il est égal à la masse du prototype international 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 washing using BIPM procedure mass deduced by extrapolation using the measured slope of µg/day (coefficient valid no more than three months). 3

4 Definition of the kilogram (II) The international prototype of the kilogram with its six official copies Four official copies from1880 Two official copies added in

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

6 Prototypes IPK manufactured in the 1880 The first 40 prototypes were distributed in 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 Comptoir Lyon-Alemand (France). Density greater than g cm 3. Adjusted to a tolerance of 1 kg 1 mg. 6

7 Manufacturing of prototypes (I) Workshop Ingot + 2 samples Density test ρ > g cm -3 Hydrostatic weighing Mass dpt Cutting process Machining + weighing Density determination 7

8 Manufacturing of prototypes(ii) Workshop Machining + weighing Cleaning-washing Mass dpt Ethanol+Ether Polishing + weighing No Weighing 1kg ± 1 mg? Yes m & ρ determined Mass evolution during 6 months 8

9 Cleaning washing of prototypes Cleaning Washing Ethanol+Ether 50 minutes 9

10 Mass evolution after cleaning (I) Mass evolution after a cleaning washing at each BIPM calibration 50 µg 10

11 Mass evolution after cleaning (II) Mass evolution after a cleaning washing at each BIPM calibration 50 µg 11

12 Mass evolution without cleaning (III) Mass evolution no cleaning washing since its manufacturing 50 µg 12

13 Traceability of BIPM working standards to the international prototype of the kilogram BIPM prototypes, BIPM 1 kg working standards in platinum-iridium and in stainless steel including also BIPM submultiples are traceable to the international prototype of the kilogram. International prototype of the kilogram Its six official copies Third periodic verification of national prototypes of the kilogram ( ) Prototypes No 25 and No 73 reserved for special uses 13

14 Traceability of BIPM working standards to the international prototype of the kilogram BIPM prototypes, BIPM 1 kg working standards in platinum-iridium and in stainless steel including also BIPM submultiples are traceable to the international prototype of the kilogram. International prototype of the kilogram Third periodic verification of national prototypes of the kilogram ( ) Its six official copies Prototypes No 25 and No 73 reserved for special uses BIPM working standards in Pt/Ir Nos 9, 31, 42,63, 77, 88, 91 and 650 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

15 Traceability of BIPM working standards to the international prototype of the kilogram BIPM prototypes, BIPM 1 kg working standards in platinum-iridium and in stainless steel including also BIPM submultiples are traceable to the international prototype of the kilogram. International prototype of the kilogram Third periodic verification of national prototypes of the kilogram ( ) Its six official copies Prototypes No 25 and No 73 reserved for special uses BIPM working standards in Pt/Ir Nos 9, 31, 42,63, 77, 88, 91 and 650 BIPM working standards in stainless steel N2, N3, J1, J2, J3 and CH1 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 to BIPM working standards in Pt/Ir carried out several times per year 15

16 Calibration procedure (I) BIPM working mass standards NMI a NMI b NMI c 2 standards 4 positions on mass exchanger Calibrated mass M1 M3 M5 M2 M4 M6 16

17 Mass evolution of prototype (I) 10 µg CW CW 17

18 Mass evolution of prototype (II) no CW since manufacturing 10 µg 18

19 Comparison between Pt/Ir Stainless steel : Corrections Air buoyancy correction 96 mg Correction due to vertical gravity gradient 3 µg m = y + (p, t, h) V + C g h + e 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, C g : 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. 19

20 Calibration uncertainty budgets Major uncertainty sources Standard uncertainty 3rd Periodic Verification 2.3 µg Stability of BIPM working standards in platinumiridium 6.6 µg Combined standard uncertainty for prototype 7 µg Major uncertainty sources Standard uncertainty Combined standard uncertainty for prototype 7 µg Air buoyancy correction between prototype and 1 kg mass standard in stainless steel Reproducibility of BIPM working standards in stainless steel Combined standard uncertainty for 1 kg mass standard in stainless steel 10.6 µg 7.0 µg 15 µg 20

21 Mass comparators (I) Comparisons Pt/Ir Pt/Ir u A < 1 µg Metrotec mass comparator Calibration Resolution of 0.1 µg Four weighing positions Air operation Mettler-Toledo M-one IPK comparison in air Future calibrations in vacuum Resolution of 0.1 µg Six weighing positions Vacuum operation 21

22 Mass comparators (II) Glove box Sartorius CCL1007 Avogadro Project and Research & Development Resolution of 0.1 µg Height weighing positions Vacuum operation VTS vacuum transfer system 22

23 Certificates issued during the last 10 years National Prototype Mass standard in stainless steel Number of certificates issued Year

24 Certificates 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 24

25 Conclusion: Calibrations Member states 25

26 Thank you for your attention! 26

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