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Euromet project 691. Calibration Inter-comparison of a 5-litre volume glass standard P. Lau. Task: ”Perform a volume calibration!”. How many laboratories? 20 from 19 countries Which volume? ”dry, contained” – below the mark ”wet, delivered or poured” How many measurements?

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Euromet project 691

Euromet project 691

Calibration Inter-comparison of a 5-litre volume glass standard

P. Lau


Task perform a volume calibration
Task: ”Perform a volume calibration!”

  • How many laboratories? 20 from 19 countries

  • Which volume? ”dry, contained” – below the mark

  • ”wet, delivered or poured”

  • How many measurements?

  • contained 18 labs: 4(1 lab)8(1 lab) 10 (14 lab)11 (1 lab) 15 (1 lab)

  • delivered 16 labs: 15 (3 lab)10(13 lab)

  • 15 laboratories performed both calibrations

  • What about cleaning? no instructions given

  • Pouring times? according to laboratory practice

  • How to report uncertainty? form but no instructions given


Result contained or dry volume
Result ”contained” or ”dry” volume

 0,01 %

mean

 2 s

median

 0,13 ml

 1,1 ml

10 measurements

11

4

8

15


Result delivered wet or poured volume
Result “delivered”, “wet” or ”poured” volume

 0,01 %

 0,16 ml

mean

 2 s

median

 1,1 ml

15

15

15

10 measurements


Uncertainty k 2 range and standard deviation
Uncertainty (k=2) – range and standard deviation

GUM

GUM

Poland

PTB

PTB

Germany

Uncertainty

BNM

-

LNE

France

BNM

-

LNE

Range

IPQ

Portugal

IPQ

Stdev

OMH

Hungary

OMH

NMI

Bulgaria

NCM

IMGC

Italy

IMGC

Slovak Rep.

SLM

SLM

Switzerland

METAS

METAS

Netherlands

NMi

NMi

United Kingdom

NWML

NWML

Turkey

UME

UME

Belgium

SMD

SMD

Denmark

FORCE

FORCE

Austria

BEV

BEV

Uncertainty

Sweden

SP

SP

Range

Czech Rep.

CMI

CMI

Stdev

Slovak Rep.

SMU

SMU

Greece

EIM

EIM

Spain

CEM

CEM

0

0

,

2

0

,

4

0

,

6

0

,

8

1

,

0

1

,

2

0

0

,

2

0

,

4

0

,

6

0

,

8

1

,

0

”contained” volume

”delivered” volume

ml

ml


Distribution of uncertainty components
Distribution of uncertainty components

1-sigma level

1,10

weighing 1

weighing 2

stdev

water density

0,70

meniscus

water density

weighing 1

weighing 2

0,53

stdev

water density

air density

weighing

0,46

meniscus

stdev

weighing

water density

0,46

meniscus

stdev

water density

weighing

0,45

meniscus

water density

stdev

weighing

0,42

0,38

meniscus

temperature

stdev

water density

komp. 1

0,37

stdev

weighing

water density

temperature

komp. 2

0,35

meniscus

temperature

water density

stdev

komp. 3

0,35

komp. 4

stdev

meniscus

water density

weighing

0,35

stdev

water density

temperature

weighing

0,31 *

stdev

weighing

water density

meniscus

0,29

stdev

water density

air density

weighing

0,26

stdev

meniscus

water density

weighing

0,22

meniscus

stdev

weighing

temperature

0,22

stdev

water density

air density

weighing

0,16 *

meniscus

stdev

water density

weighing

0,14

weighing

water density

stdav

meniscus

0,13

stdev

temperature

weighing 1

weighing 2

U(contained volume)

* values for

GUM & PTB

refer to

delivered volume


Cross correlation degree of equivalence
Cross-correlation – “degree of equivalence”

±2 s

area

CMI

BNM-LNE

SMU

SLM

PTB

GUM


Uncertainty declaration
Uncertainty declaration

  • Just one figure – Force (1)

  • 5 components – SMD, NWML (2)

  • 6 components – Metas, UME (2)

  • 7 components – IPQ, BNM-LNE, SMU, NMi, BEV (5)

  • 8 components – CMI, SLM, CEM, OMH (4)

  • 9 components – SP, GUM, NCM (3)

  • 11 components – EIM (1)

  • 14 components – PTB (1)


Possible conclusions from the
Possible conclusions from the

  • The total outcome is satisfactory.

  • One lab out of 20 (5 %) (in 35 results) just outside 95 % confidence level.

  • Large difference in repeatability between the laboratories (is low spread always good?).

  • Large difference in uncertainty declarations.

  • Some results (at least 5 for dry and 6 for wet volume) are unrealistic small.

  • Probably 3 to 5 components really matter.

  • A good and realistic uncertainty estimation depends more on a ”feeling” than on a sophisticated modelling.

  • In the perspective of an inter-comparison systematic effects (connected with a method) are serious uncertainty contributions (cleaning, pouring, experimental realization).

  • The meniscus setting is very personal (random within laboratory – systematic in global aspect).

  • In my opinion uncertainty declarations need to incorporate the limitations of a calibration object.


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