Supplementary Comparison - BIPM · SUPPLEMENTARY COMPARISON CALIBRATION OF MASS AND CONVENTIONAL MASS SIM.M.M-S13 2 de 13 FINAL REPORT SUPPLEMENTARY COMPARISON CALIBRATION OF MASS

SUPPLEMENTARY COMPARISON CALIBRATION OF MASS AND

CONVENTIONAL MASS SIM.M.M-S13

1 de 13

FINAL REPORT

Supplementary Comparison

CALIBRATION OF MASS AND CONVENTIONAL MASS

OF WEIGHTS

BETWEEN INACAL - CENAM - CESMEC

(2 kg and 10 kg)

SIM.M.M-S13

September 2017

FINAL REPORT

SIM.M.M-S13

Index Page 1 Introduction 2 2 List of participants NMIs 2 3 Travelling weight standards 3 4 Circulation Schedule 3 5 Surface damages of the standard 4 6 Measurement conditions 4 7 Procedures and measurement methods 5 8 Measurement results 5 9 Results analysis 8 10 Results for mass 10 11 Results for conventional mass 11 12 Conclusions 12 13 Acknowledgments 12 14

References 13



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FINAL REPORT

SUPPLEMENTARY COMPARISON

CALIBRATION OF MASS AND CONVENTIONAL MASS OF WEIGHTS

BETWEEN INACAL - CENAM - CESMEC

(2 kg and 10 kg)

SIM.M.M-S13

Luz Cori Almonte1, Donny Taipe Araujo1, Aldo Quiroga Rojas 1, Luis Omar Becerra2, Luis Manuel Peña2,

Fernando Garcia3, Francisco Garcia3.

1 Instituto Nacional de Calidad, INACAL / Perú 2 Centro Nacional de Metrología, CENAM / México

3 Centro de Estudios de Medición y Certificación de Calidad, CESMEC / Chile

1. Introduction

This report describes the results of the supplementary comparison of 2 kg and 10 kg stainless steel mass standard between INACAL-PERÚ, CENAM-MEXICO and CESMEC-CHILE.This comparison was undertaken by INACAL, CENAM and CESMEC, was based on a decision taken on August, 2012. The supplementary comparison was piloted by INACAL- PERÚ. This comparison was registered as an official supplementary comparison under the designation SIM.M.M-13. The reference values were provide by CENAM-MEXICO. The travelling weight standards belonged to INACAL-. They were OIML E2 weights. The travelling weight standards were prepared by INACAL. INACAL measured the volume of the travelling standard of 10 kg and PTB measured the volume of the travelling standard of 2 kg. The travelling weight standards were circulated between the NMIs. Each NMI determined their mass and uncertainty using their procedures and methods. The measurements were carried out from September 2012.

2. List of participant NMIs

The participating laboratories and their respective technical contacts are listed below: • Instituto Nacional de Calidad - INACAL, Perú (*)

Luz Cori Almonte Donny Taipe Araujo Aldo Quiroga Rojas

(*) Before June 01st 2015, the Peruvian NMI was the Instituto Nacional de la Competencia y de la Protección de la Propiedad

Intelectual - INDECOPI



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• Centro Nacional de Metrología - CENAM, México

Luis Omar Becerra Luis Manuel Peña

• Centro de Estudios de Medición y Certificación de Calidad - CESMEC, Chile

Francisco García Fernando García

Raúl Hernández 3. Travelling weight standards

The travelling standards used were OIML Class E2 weights belonging to INACAL, with the following nominal values of 2 kg and 10 kg. The shape and material of travelling weight standards are shown in Table 1.

Table 1

Nominal value Accuracy Class Material Shape

2 kg E2 Stainless Steel Cylindrical w ith a lif ting knob

10 kg E2 Stainless Steel Cylindrical w ith a lif ting knob

In August 2012, the volume of the mass of 10 kg was determined in the laboratory INACAL. The volume of the mass of 2 kg was measured in the PTB. These results were provided to participating laboratories and are shown in Table 2.

Table 2: Information about of the travelling weight standards

Identification Manufacturer Nominal Value Volume at

20 °C cm

3

Uncertainty k=2

cm3

50703712 SARTORIUS 2 kg 254,73 0,04

212 KERN 10 kg 1265,9 0,8

4. Circulation Schedule

The circulation schedule of the travelling weight standards are shown in tables 3 and 4. INACAL started the measurements in September 2012 and the last measurements were also made by INACAL in September 2014. The original schedule was modified due to difficulties in the transportation and retention of the standards at customs in some countries.

Table 3: 2 kg weight

Laboratory Period of measurements

Instituto Nacional de Calidad - INACAL 1, Perú 2012-09

Centro Nacional de Metrología - CENAM, México 2012-09

Centro de Estudios de Medición y Certif icación de Calidad CESMEC, Chile

2013-02

Instituto Nacional de Calidad - INACAL 2, Perú 2013-03



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Table 4: 10 kg weight

Laboratory Period of

measurements

Instituto Nacional de Calidad – INACAL1, Perú 2012-10

Centro de Estudios de Medición y Certif icación de Calidad - CESMEC, Chile

2013-02

Centro Nacional de Metrología - CENAM, México 2014-01

Instituto Nacional de Calidad – INACAL 2, Perú 2014-12

5. Surface damages of the standards:

The traveling standards were examined by each NMI at the reception and departure of the weights in order to register all marks and damages during circulation. The participating laboratories sent to the pilot laboratory the forms used to register the superficial conditions of the traveling standards, at both reception and departure. The data sent by the participating laboratories showed that there was no significant damage on the traveling standards

6. Measurement conditions

The environmental conditions for determination of the mass and conventional mass reported by the participating laboratories are listed in table 5.

Table 5

INACAL 1 CENAM CESMEC INACAL 2

2 kg 10 kg 2 kg 10 kg 2 kg 10 kg 2 kg 10 kg

T (º C) 22,70 21,00 21,09 20,02 23,65 23,4 20,45 20,81

ΔT/h (ºC) 0,08 0,23 0,20 0,16 0,1 0,0 0,25 0,32

H / tr 51,85 47,33 9,56 °C 10,12 °C 56,85 58,6 57,0 56,7

ΔH / Δtr (51,7-52,0)% (48,0-46,7)% (9-10) °C (10-11) °C (57-57)% (57-60)% (57-57) % (56-57) %

ρa(kg/m3) 1,1655 1,1760 0,9545 0,9580 1,1005 1,1009 1,1695 1,1685

The resolutions of the weighing instruments, used by the different laboratories, are showed in Table 6.

Table 6

Units in mg INACAL 1 CENAM CESMEC INACAL 2

2 kg 0,1 0,2

0,01 0,1 0,01 0,2

10 kg 0,2

5 0,01 1

0,2

5

The resolutions of the environmental conditions, used by the different laboratories, are shown in table 7.

Table 7


TEMPERATURE 0,01 °C 0,001 °C 0,1 °C 0,01 °C

PRESURE 0,1 mbar 1 Pa 1 pa 0,1 mbar

HUMIDITY 0,1 % 0,1 % 0,1 % 0,1 %



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Table 8 shows the traceability of the mass standards used by the NMIs, to indicate the possible correlation of the traceability source of the standards.

Table 8


2 kg CEM CENAM PTB CEM

10 kg NRC CENAM PTB CENAM

The 10 kg mass standard used by INACAL was traceable to NRC (INACAL 1) and traceable to CENAM (INACAL 2). The dates of calibration of the mass standards used for the measurements are listed in table 9. An overdue calibration date could introduce a drift that may affect the results of the calibration.

Table 9


2 kg 2012 2012 2011 2014

10 kg 2012 2014 2011 2014

7. Procedures and measurement methods

The measurement method used by laboratories CENAM and INACAL was the subdivision method. CESMEC used the direct comparison method. INACAL uses a least squares method to obtain the results by means of the Gauss-Markov estimation, using weights of different nominal value. This method involves solving an oversized system of equations. CENAM used the subdivision procedure, starting from one kilogram and generating a set of independent measurements that is modeled by a system of linear equations and the solution to this set of equations was found by the technique of least squares. The mass values and their respective uncertainties for the travelling weight standards were obtained by subdivision method. Matrix solution by weighted least squares was applied to the weighing scheme. The density of the air was calculated by equation CIPM-2007 and the approximation formula for air density, according to table 10.

Table 10

Laboratory Equation

INACAL CIPM-20071

CENAM CIPM-20071

CESMEC Approximation formula

for air density2



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8. Measurements results

Table 11 shows the mass correction found by the NMIs and its associated uncertainty for a confidence level of 95,45 %. 1Rev ised f ormula f or the density of moist air (CIPM-2007) [2] 2OIML R111, E.3. [1]

Table 11: Mass correction

Participant

laboratory

2 kg 10 kg

Reference

Value

mg

mA

mg

UA (k=2)

mg

Reference

Value

mg

mA

mg

UA (k=2)

mg

INACAL 1

5,93

5,88 0,23

18,82

18,0 4,6

CENAM 5,93 0,124 18,82 1,54

CESMEC 8,1 1,0 21,7 5,0

INACAL 2 5,79 0,31 17,0 4,8

Table 12 shows the conventional mass correction found by the NMIs and its associated uncertainty for a confidence level of 95,45 %.

Table 12: Conventional Mass correction

Participant laboratory

2 kg 10 kg

Reference

Value

mg

mA

mg

UA

(k=2)

mg

Reference

Value

mg

mA

mg

UA

(k=2)

mg

INACAL 1

0,255

0,21 0,23

-0,27

-1,1 4,6

CENAM 0,255 0,124 -0,27 1,54

CESMEC 2,3 1,0 2,6 5,0

INACAL 2 0,12 0,31 -2,1 4,8

The average value was obtained by the pilot laboratory considering the drift obtained, measuring the mass correction at the beginning and end of the comparison. For this the following equations were used:

2

12 PLPLPL

mmm

(8.1)

where: mPL1: Mass (or conventional mass) correction value measurement 1, by INACAL the pilot

laboratory mPL2: Mass (or conventional mass) correction value measurement 2, by INACAL the pilot

laboratory

2

122

2

32)()(

PLPL

PLPL

mmmumu (8.2)

)()( PLPL mukmU (8.3)



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Tables 13 and 14 shows the average value of pilot laboratory

Table 13: Mass correction

Pilot laboratory

2 kg 10 kg

mA

mg

U (k=2)

mg

mA

mg

U (k=2)

mg

INACAL 5,84 0,31 17,5 4,8

Table 14: Conventional Mass Correction

Pilot

laboratory

2 kg 10 kg

mA

mg

U (k=2)

mg

mA

mg

U (k=2)

mg

INACAL 0,16 0,31 -1,6 4,8

Uncertainty analysis has been made for all NMIs according to GUM. The uncertainty contributions assigned by the NMIs for each nominal value are shown in tables 15 and 16 respectively, according to the format established in Annex D of the Technical Protocol.

Table 15: Uncertainty contributions reported by the NMIs for 2 kg weight

NOMINAL VALUE 2 kg INACAL 1 CENAM CESMEC INACAL 2

INFLUENCE MAGNITUDE Xi

UNIT u

k=1 u(xi)

u k=1 u(xi)

u k=1 u(xi)

u k=1 u(xi)

Mass of standard, P mg 0,0280 0,057 0,15 0,0800

Drift of standard, δP mg 0,0179 0,0012 0,0294

Volume of standard, Vp cm3 0,0233 0,0234

Density of mass standard 0,0048 0,003881

Volume of sample Vm cm3 0,0233 0,0234

Density of sample m 0,019 0,12

Air density, ρa mg/cm3 0,0056 0,00074 0,004 0,0056

Sensibility of the balance 0,010

Resolution of balance mg 0,0749 0,0041 0,028 0,0687

Repetibility mg 0,0702 0,0033 0,02 0,0548

Weighing process (fitt ing) mg 0,0212 0,0050 0,0902

Reproducibility cm3 0,0022

Combined uncertainty mg 0,115 0,062 0,5 0,156



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Table 16: Uncertainty contributions reported by the NMIs for 10 kg weight

NOMINAL VALUE 10 kg INACAL 1 CENAM CESMEC INACAL 2

INFLUENCE MAGNITUDE Xi

UNIT u

k=1 u(xi)

u k=1 u(xi)

u k=1 u(xi)

u k=1 u(xi)

Mass of standard, P mg 0,11000 0,60 0,8 0,2200

Drift of standard, δP mg 0,09238 0,29 0,0981

Volume of standard, Vp cm3 0,01764 0,0175

Density of mass standard mg/cm3 0,025 0,019684

Volume of sample Vm cm3 0,47049 0,4674

Density of sample m mg/cm3 0,38 0,019150

Air density, ρa mg/cm3 0,01740 0,0032 0,015 0,0169

Sensibility of the balance mg 0,010

Resolution of balance mg 2,04257 0,0041 0,3 2,0429

Repetibility mg 0,81125 0,0074 0,4 0,8837

Weighing process (fitt ing) mg 0,64847 0,0063 0,5994

Reproducibility cm3 0,0071

Combined uncertainty mg 2,34 0,77 2,5 2,36

Most of the laboratories considered the same influence magnitudes (uncertainty contributions) for the estimation of the uncertainty. This guarantees a greater homogeneity in the determination of the combined uncertainty.

9. Results Analysis

The aim of the comparison is to demonstrate the consistency between the results provided by the laboratories and the reference values. The reference values for this comparison were determined by the CENAM with an expanded uncertainty (k=2). The results were sent directly to the pilot laboratory

(INACAL). The uncertainty values associated with the mass measurements, reported by the participating laboratories, are listed in Table 17.

Table 17

NOMINAL

VALUE

2 kg 10 kg

U (k=2) mg

U (k=2) mg

INACAL 0,31 4,8

CENAM 0,12 1,5

CESMEC 1,0 5,0

9.1 Drift uncertainty Ud

A drift uncertainty Ud for the mass instability of the travelling weight standards is

taken into account with the following equation:



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2

12

32

PLPL

d

mmkU (9.1)

where: mPL1: Mass (or conventional mass) correction value measurement 1, by INACAL the pilot laboratory mPL2: Mass (or conventional mass) correction value measurement 2, by INACAL the pilot laboratory

Note: The uncertainty due to instability, Ud, was obtained from the measurements made by the pilot laboratory, INACAL, at the beginning and at the end of the comparison.

In order to evaluate the degrees of equivalence of the results given by the participating laboratories, it was necessary to calculate the normalized error of measurement in relation to the reference value, and its associated uncertainty, according to the equation (9.2).

222RdA

RAn

UUU

mmE

(9.2)

En Normalized error

mR The reference value, CENAM

UR The expanded uncertainty of the reference value with k = 2 , CENAM

mA the NMI value

UA the expanded uncertainty of the NMI value with k = 2

9.2 Evaluation of the consistency of the comparison

This dimensionless value should be smaller than 1. It allows comparison of the results of the participants with different uncertainties and allows the appreciation of the consistency of the obtained measurement results ( IEnI ≤ 1).

Table 18, expresses the normalized error calculated according to equation (9.2) from the results of the NMIs for each nominal value in mass.

Table 18

NMIs NOMINAL

VALUE

|𝑬𝒏|

mg

|𝑬𝒏| ≤ 𝟏

INACAL 2 kg

0,3 YES

CESMEC 2,1 NO

INACAL 10 kg

0,2 YES

CESMEC 0,5 YES

Table 18, shows that the IEnI value for CESMEC is greater than 1 for 2 kg .



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The difference between the laboratory result mA and the reference value m

R is

calculated by:

Di = m

A- m

R (9.3)

This parameter Di is called the difference from the reference value.

Every Di is associated with an uncertainty given by the following formula,

u²(Di) = uA² +ud – uR

²

(9.4)

The same notation is used for both mass and conventional mass results in Sections 10 with the meaning set by the context.

10. Results for mass

10.1 2 kg

The results for the transfer standard of 2 kg are contained in the following table:

Table 19

NMIs NOMINAL

VALUE 𝑫𝒊 mg

𝑼(𝑫𝒊) mg

CENAM

2 kg

0,00 0,124

INACAL -0,09 0,34

CESMEC 2,17 1,01

The values D

n and their corresponding uncertainties U(D

n) (k = 2) are shown in the

following graph 1:



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Graph 1

10.1 10 kg The results for the travelling standard of 10 kg are given in the following table:

Table 20

NMIs NOMINAL

VALUE 𝑫𝒊 mg

𝑼(𝑫𝒊)

mg

CENAM

10 kg

0,0 1,54

INACAL -1,3 5,1

CESMEC 2,9 5,2

The values D

n and their corresponding uncertainties U(D

n) (k = 2) are shown in the

following graph:

Graph 2

11. Results for conventional mass

11.1 2 kg

The results for the travelling standard of 2 kg are given in the following table:

Table 21

NMIs NOMINAL

VALUE 𝑫𝒊 mg

𝑼(𝑫𝒊)

mg

CENAM

2 kg

0,00 0,124

INACAL -0,09 0,34

CESMEC 2,05 1,01



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The values Dn

and their corresponding uncertainties U(Dn) (k = 2) are shown in

the following graph:

Graph 3

11.2 10 kg

The results for the travelling standard of 10 kg are given in the following table:

Table 22

NMIs NOMINAL

VALUE 𝑫𝒊 mg

𝑼(𝑫𝒊)

mg

CENAM

10 kg

0,00 1,54

INACAL -1,3 5,1

CESMEC 2,9 5,2

The values Dn

and their corresponding uncertainties U(Dn) (k = 2) are shown in

the following graph:



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Graph 4

12. Conclusions

The comparison was successful. There was no significant deviation in the measured mass of any of the travelling weight standards. The participant results were reported according to the protocol. For laboratory CESMEC, the normalized error for 2 kg weight is greater than 1, this is shown in the table 18. In graphs 1, 2, 3 and 4 are shown the difference of the participating laboratories with respect to the reference laboratory, CENAM, and their expanded uncertainties with k=2.

13. Acknowledgments

We would like to thank to Gregorio Alvarez Clara from CENAM for his valuable contribution on the measurements of the travelling weight standards involved in this comparison.

14. References

[1] OIML R111, Weights of classes E1, E2, F1, F2, M1, M2, M3, 2007 [2] Revised formula for the density of moist air (CIPM-2007); Metrologia 45 (2008)

149-155. [3] JCGM 100:2008, Evaluation of measurement data - Guide to the expression of

uncertainty in measurement, 2008. [4] http://www.bipm.org/utils/common/documents/CIPM-MRA/CIPM-MRA-D-05.pdf [5] EA-4/02, Expression of the Uncertainty of Measurement in Calibration, 1999

http://www.european-accreditation.org/n1/doc/ea-4-02.pdf [6] Wolfang Wöger, Remarks on the En – Criterion Used in Measurement

Comparison, PTBMitteilingen 109 1/99, Internationale Zusammenarbeit [7] ISO/IEC 17043:2010, Conformity assessment -- General requirements for

proficiency testing.

http://www.european-accreditation.org/n1/doc/ea-4-02.pdf

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Supplementary Comparison - BIPM · SUPPLEMENTARY COMPARISON CALIBRATION OF MASS AND CONVENTIONAL MASS SIM.M.M-S13 2 de 13 FINAL REPORT SUPPLEMENTARY COMPARISON CALIBRATION OF MASS