prof. tariq a. aldowaisan - kuwait flow measurement...
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Prof. Tariq A. Aldowaisan
Gulf Lead Consultants
Measurement Uncertainty in ISO 17025
TARIQ ALDOWAISAN Founder & Senior Consultant, Gulf Lead Consultants
Prof. Tariq A. Aldowaisan
• Ph.D. in industrial & management systems engineering (IMSE) from ASU, USA
• Professor of IMSE at the College of Engineering & Petroleum, KU
• Founder and senior consultant at Gulf Lead Consultants.
• Certified Quality Engineering (CQE), Certified Manager of Quality/ Organizational Excellence (CMQ/OE), and Certified Quality Auditor (CQA) from American Society for Quality (ASQ).
• Certified Safety Professional (CSP), Associate Safety Professional (ASP), and Certified Environmental, Health and Safety Trainer (CET) from Board of Certified Safety Professionals (BCSP).
• Has over 25 years experience in quality, organizational excellence, and safety.
What is a MU Estimate?
“parameter, associated with the result of a
measurement, that characterizes the dispersion of
the values that could reasonably be attributed to the
measurand”
This parameter is typically _______ or _________
SD Width of a CI
International Vocabulary of basic and general standard terms in Metrology (1993)
1
2
n
xXSD
Measurement result
Reference value
Precision (mu)
Bias
−𝑘𝑠 +𝑘𝑠
Result of Test or Measurement Method
Accuracy/ Error
Trueness Bias
Precision
Repeatability Reproducibility
Ref. ISO 21748:2010
Trueness/Bias (Systematic Error)… Difference between the expectation of a test result
or measurement result and a true value
Precision (Random Error)… Closeness of agreement between independent
test/measurement results obtained under stipulated conditions
Repeatability … Precision under repeatability conditions (same test procedure, same
operator, same test equipment under same conditions, same location, repetition over a
short period of time)
Reproducibility… Precision under reproducible conditions (same test method on
identical test items in different test facilities, with different operators using different
equipment)
Uncertainty
Ref. ISO 21748:2010
Uncertainty … is SD or a multiple of SD
Standard uncertainty … is SD of the result of a measurement
Uncertainty budget … is list of sources of uncertainties and their
associated standard uncertainties
Combined standard uncertainty … positive square root of sum of
variances or covariances of result’s affecting quantities
Expanded uncertainty … interval capturing a large fraction of the
values that could reasonably be attributed to the measurand
Coverage factor (k) … numerical factor used as a multiplier of the
combined standard uncertainty
MU Estimation Methods Two Approaches
MU Estimation Approaches
GUM Approach
Collaborative Study Approach
• The GUM is ________, yet __________.
• The Collaborative Study is less ___________, yet _________.
Therefore, in practice it is ____________ over GUM.
ideal difficult
rigorous easier
preferred
ISO Guide to the Expression of
Uncertainty in Measurement
(GUM)
‘bottom-up’ approach ‘top-down’ approach
The GUM Approach ‘predicts the uncertainty in the form of a variance on the basis of
variances associated with inputs to a mathematical model. The other (Collaborative
Study Approach) uses the fact that, if those same influences vary representatively
during the course of a reproducibility study, the observed variance is a direct estimate of
the same uncertainty.’ ISO 21748:2010, p.24.
ISO 17025 4.1 Organization
4.2 Management
System
4.3 Document Control
4.4 Review of request
and contacts
4.5 Subcontracting of Tests & Calibration
4.7 Service to the
Customer
4.8 Complaints
4.9 Control of Nonconforming Testing &Calibration Work
4.13 Control of records
4.12 Preventive Action
4.11 Corrective Action
4.10 Improvement
4.14 Internal Audits
4.6 Purchasing Services
and Supplies
5.2 Personnel
5.3 Accommodation and Environmental Conditions
5.4 Test and Calibration Methods and Method
Validation
5.5 Equipment
5.6 Measurement Traceability
5.7 Sampling
5.8 Handling Test and Calibration Items
5.9 Assuring the Quality of Test and Calibration
Results
5.10 Reporting of Results
5.1 General
MU in ISO 17025
5.4.6.3 Take all uncertainty components into account
5.4.5.3 MU is part of methods validation
33 Times
5.4.6.2 When not possible to rigorously estimate MU, …
5.4.6 Estimation of uncertainty of measurement
5.4.4 Estimation of MU in new tests
5.10.3.1 MU statement in test reports
Conclusion
1. Reporting a test result without MU is meaningless
2. MU is key to complying with ISO 17025