OBJECTIVE
TARGET GROUP TECHNICIANS, ENGINEERS AND SCIENTISTS, INVOLVED IN
MEASUREMENT FOR CALIBRATION, TESTING, INSPECTION, TRADE
OR RESEARCH
DURATION
PRESENTER
CANDIDATE WILL BE ABLE TO EVALUATE AND REPORT THE
UNCERTAINTY OF MEASUREMENTS AND CALIBRATIONS IN
ACCORDANCE WITH INTERNATIONALLY ACCEPTED BEST PRACTICE
AND COMPLIANT WITH THE ISO17025 LABORATORY
ACCREDITATION STANDARD
3 DAYS (3 X 7 HOURS) + 1 DAY REVIEW SESSION AND EXAM
Pieter de la Court (MSc Technical Physics, Metrologist)
INTRODUCTION
Measurements are done by many people, on any conceivable physical quantity and for a great multitude of purposes. The results are used to increase understanding of a subject, to check if a certain property is within design specifications, to determine the quantity or quality of a product or commodity in a commercial transaction, to control processes, to predict future events and developments, etc.
In many cases decisions are taken on the basis of information from measurements and such decisions may have grave consequences in terms of money, human safety and health, environmental protection, and so on. It is therefore of paramount importance that the measurement results on which the decisions are based are reliable and dependable.
It is however technically impossible to make a perfect measurement. The measurement result is not exact, but will always deviate by a smaller or larger amount from the actual “true” value. This deviation is fundamentally an unknown factor, because it is the difference between the actual measurement result and the true value. The true value is also unknown (if we knew it, we would not need to do the measurement). The best thing we can do is to determine as well as possible the limitations to the accuracy, or in other words, the likely magnitude of the possible deviation.
This is expressed by the uncertainty of measurement, the degree to which we are uncertain about the result. The uncertainty is a quantitative expression of the quality of a measurement result. In order to make valid decisions or conclusions on the basis of measurement results, the uncertainty of measurement is of crucial importance, since it allows one to determine if there are any risks of a wrong conclusion and, if so, to calculate the probabilities of such risks.
In the past there has been much confusion about the evaluation and interpretation of measurement uncertainty, in those days often called “error analysis”, until during the 1980’s an international group of technical experts worked out the theoretical understanding as well as a practical approach, under the ISO Technical Advisory Group 4. This resulted in the “Guide to the
Expression of Uncertainty in Measurement”, generally referred to as the “GUM”, published in
1993, with a corrected and improved revision in 1995. The method proposed in this document has been universally adopted by metrology laboratories world-wide. Any calibration results should be analysed using this method and increasingly in quantitative testing the method is also being prescribed. Applying the GUM method to test and calibration measurements is a requirement of the ISO/IEC17025 standard for the accreditation of calibration laboratories.
The GUM is considered to be a very theoretical and “difficult” book, only suitable for the highest levels of metrology. Yet the method is applicable to all levels of metrology. As a result there are a growing number of documents that interpret and apply the GUM method in a simplified way.
There are several documents that adapt the GUM method for specific fields of measurement or testing, e.g. in pharmaceutical and medical laboratories.
Pieter de la Court - Metrology Consult
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Many of these documents are freely available from the Internet. This course will make use of the document EA 4/02 from the European Co-operation for Accreditation, which is a distillation of the essential components of the GUM, but also includes very useful worked-out examples.
This course introduces the method for the evaluation and expression of uncertainty, according to the systematic approach of the GUM and its derived, simplified documents; it involves a considerable practical component, training the participants to be able to independently perform the uncertainty analyses on calibration and test measurements. Theory will only be covered as far as necessary for the understanding of the practical techniques. The use of spreadsheets (MS
Excel) for the calculation of the uncertainty will also be shown.
The GUM method is generally applicable to any field of measurement and most types of quantitative testing.
PREREQUISITE KNOWLEDGE
Participants are assumed to have a certificate, diploma or degree in a relevant technical subject and some experience with calibration or testing.
It will be an added advantage to have attended an introductory training course in metrology, such as “General Metrology” or “Metrology for All”, available from QMMC.
COURSE CONTENT AND TENTATIVE SCHEDULE
DAY 1, MORNING
REGISTRATION
INTRODUCTIONS
1. The basics of the GUM method, theory with examples
1.1. Problem definition
1.2. The procedure (recipe)
1.3. The uncertainty budget (table)
1.4. Type-A analysis
1.5. Using a scientific calculator / MS Excel for type-A evaluation
1.6. Exercise type-A evaluation
DAY 1, AFTERNOON
1.7. Type-B analysis
1.8. Probability distributions
1.9. Examples of probability distributions
1.10. Sensitivity coefficients
1.11. Exercise sensitivity coefficients
DAY 2, MORNING
1.12. Presentation of the result
1.13. Summary and recap
2. Worked examples of complete uncertainty evaluations
2.1. Example 1 (to be selected with relevance to the field of work of the participants)
2.2. Example 2 (to be selected with relevance to the field of work of the participants)
DAY 2, AFTERNOON
3. Using instrument specifications
3.1. Specs or calibration data, what to use
3.2. Examples
3.3. Testing against specifications and TUR
3.4. Exercises on the use of instrument specs
Pieter de la Court - Metrology Consult
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4. Exercises: complete uncertainty evaluation
Examples of limited complexity will be selected according to the field of metrology in which the participants are active. This may include: mass, length, volume, electrical, pressure, temperature, optical measurements; calibration, testing or legal metrology. About two to four examples will be worked out in small groups, depending on the number of participants.
DAY 3, MORNING
5. Exercises (continued) and discussion of answers
6. Degrees of freedom and Student Distribution
DAY 3, AFTERNOON
7. Correlated input quantities (optional)
8. Where to get more information
9. Course recapitulation and evaluation
10. Handing out of assignments
REVIEW SESSION (ABOUT THREE WEEKS AFTER DAY 3)
MORNING
11. Review of assignment papers
12. Discussion and questions
13. Recap of the course content
AFTERNOON
14. Final Test
COURSE FORMAT AND MATERIALS
The course consists of PowerPoint presentations on theory, examples worked out by the presenter and exercises to be done by the participants, with plenary discussions on the results.
At the end of the course, the participants will be given an assignment to be submitted within about two weeks, which will be discussed during the review session. On the same day of the review session a 3-hour exam will be conducted.
Course materials include hard copies of the presentations, exercise sheets and a copy of the EA
4/02: “Expression of the Uncertainty of Measurement in Calibration”.
Participants are required to bring a scientific calculator with statistical functions or a laptop, installed with MS Excel package (preferred).
TESTIMONIAL
A certificate of training will be issued to participants who have attended the course in full and have obtained sufficient marks for the assignment and the test. Those who submitted insufficient quality of work or incomplete results will receive a certificate of attendance.
Pieter de la Court - Metrology Consult
Brochure Uncertainty – v1.2, September 2014
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