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7/30/2019 Metrological traceability DeBievre
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7/30/2019 Metrological traceability DeBievre
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©P De Bièvre CITAC Sydney Oct1999
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t r a c e a b i l i t y
What istraceability ?
7/30/2019 Metrological traceability DeBievre
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©P. De BièvreStenungsundNov 1998
Key 1 for Metrology in Chemical Measurement:
Traceability
property of the result of a measurement or the
value of a standard whereby it can be relatedto stated references, usually national or
international standards, through an unbroken
chain of comparisons all having stateduncertainties
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VIM 1993
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©P De Bièvre Chemand Law Wien Sep 1999
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0.00
0.05
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0.15
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0.25
0.30
0.35
0.40
0.45
0.50
0.55
c
m m o l · k g - 1
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
D e v i
a t i o n f r o m m
i d d l e o f c e r t i f i e d r a n g
e i n %
Experienced laboratory (self-declaration)
Less experienced laboratory (self-declaration)
Non experienced laboratory (self-declaration)
No statement by laboratory
Pb
Results from all participants.
IMEP- 10 : Trace Elements in PolyethyleneCerti fied range [ U =k ·u c (k =2)]: 0.449 - 0.491 mmol·kg
-1
©IMEP CCQM Orlando Feb 1999PORTOROZ Sep 2002
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example of TMU of 15%
around Reference Range
7/30/2019 Metrological traceability DeBievre
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©P. De Bièvre Sao Paolo Dec 1998
Key 2 for Metrology in Chemical Measurement:
Type A evaluation:method of evaluation of a standarduncertainty by the statistical analysis
of a series of observationsType B evaluation:
method of evaluation of a standard
uncertainty by means other than thestatistical analysis of a series of observations
Uncertainty
ISO BIPM GUM 1993
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©P De Bièvre KASTERLEE Feb 2002RIO de J ANEIRO Apr 2002
EILAT Nov 2003
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Current revision of the VIM:
1. improvement through decrease of - inconsistencies:
•internal within VIM•internal within ISO Guides and Standards
•external between ISO- and non-ISO documents
•no clarity
•no understanding
•no agreement possible
in trade
in implementation of EC Directives
in mutual acceptance of measurement results
- unclarities, since: ...
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©P De Bièvre KASTERLEE Nov 2002EILAT Nov 2003
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The (revision of VIM-2, yielding) VIM-3
2. takes on board chemical measurement
3. uses the “substitution principle”:any definition of a term for the definition of a concept must becapable of replacing that term in another definition
4. uses GUM, even if a number of GUM terms for concepts isalready up for refinement in “GUM-2” (which is not yet planned)
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©P De Bièvre KASTERLEE Nov 2003
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The (revision of VIM-2, yielding) VIM-35. obviously still suffers from a carry-over from 20th - and even19th - century thinking
6. contains “counting quantities is an implicit base quantity”
7. makes uncertainty part of the measurement result8. defines “metrological traceability”9. defines “traceability to the SI”10. defines “measurand” as a “quantity intended for measurement11. includes thinking in terms of “chemical measurement”
(for the first time !)12. includes examples of chemical measurements
(for the first time)13. introduces “calibration hierarchy”14. gives a definition of “comparability”15. specifies any “CRM” as a “measurement standard”
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©PDB KASTERLEE Feb 2003
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Some examples justifying a revision:
example 1: “measurand”
example 2: “measurement result”
example 3: “metrological traceability”
example 4: “measurement uncertainty”
example 5: “measurement unit” and “measurement scale”
example 6: “metrological comparability”
example 7: “target measurement uncertainty”
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Key 2: Measurement uncertainty (MU)
Measure of doubt about the measurement result.
1. an uncertainty of a measurement result is generated automatically
from the very moment one starts measuring
2. measurement uncertainty is obtained through an evaluation process:
- type A evaluation
- type B evaluation
(calculation comes only in at the end, after evaluation)
©P De Bièvre BUCURESTI - MARIBOR - EL QUAHIRA Sep 2001
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3. understanding the process called measurement, is a prerequisite for evaluation of measurement uncertainty
4. measurement uncertainty should be small enough for the intended
use but, need not be smaller (it can, but need not be smaller)
©P De Bièvre BUCURESTI - MARIBOR - EL QAHIRA Sep 2001 TALLINN Mar 2002
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©P Taylor GEEL J an 1998
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Uncertainty is new to chemists !
•absent in most university curricula
•ISO/BIPM guide (GUM): only 12 years old !•Repeatability is thought of as uncertainty
•Terra incognita !
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©P. De Bièvre SAPUZ Zürich J uly 1999
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ISO/BIPM-guide:
the new approachre-establishes the responsibility
of the analyst because“evaluation of uncertainty”
is a thinking process !
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©P. De BièvreGeelNov 1992
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DISCREPANCY
PROBLEM NO PROBLEM
DISCREPANCY PROBLEMS CAN BE CAUSED
UNNECESSARILY BY LACK OF
” ORTHODOX” UNCERTAINTY ASSESSMENT
NO DISCREPANCY
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©P De Bièvre KASTERLEE 2004
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©P. De Bièvre Sao Paolo Dec 1998
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Metrology
creates
respect for the law
Lack of Metrology
creates
contempt of the law
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©P De Bièvre SAPUZ ZÜRICH J uly 1999
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The task is
to demonstrate
the authority of the result
of the measurement.
This needs
underpinning (“ Untermauerung” )
of the measurement result
in order to lead tothe necessary credibil ity.
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Key 3: Target Measurement Uncertainty (TMU)
Range of uncertainties from which the analyst claims it contains a
specified “traceable” value for the measurand
1. The analyst needs a “target” for the measurement uncertainty
he must attempt to achieve
2. A TMU usually originates from a requirement put down byregulatory authorities
©P De Bièvre BUCURESTI - MARIBOR - EL QUAHIRA Sep 2001
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©I SKUBIC PORTOROZ Sep 2002
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TMU
!
M e s u r e m e n t
c o s t
increasing QL
increasing TMU
QL
TMUo
MCo
QLo
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©P Taylor GEEL Sep 1999
Metrology in chemistry :The Hubble telescope ...
= the ‘spectacles’ of the analytical chemist
BEFORE AFTER