Measurement & Uncertainty - Basic concept and its application

Transcription

1 Measurement & Uncertainty - Basic concept and its application Feb JongOh CHOI (choijongoh@kriss.re.kr)

2 Knowledge and measurement When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of science, whatever the matter may be. Sir William Thomson, Lord Kelvin ( )

3 , etc Make it measurable!! Head, Center of Standards and Quality management Chair, Uncertainty committee of KRISS Education Ph. D. Analytical Chemistry, (1992) M. Eng. Chemical Engineering, (1983) B. Eng. Chemical Engineering, (1981) Field of Interest - Quality of Management (2005 -) - Vocabulary in Metrology (2004 -) - Uncertainty in Measurement (2003 -) - Reliability of Chemical measurement (National Research Laboratory 1999) - Analytical chemistry More than 260 Lectures on Measurement & Uncertainty, Reference Materials, PT, QMS, etc

4 No argument on measurement results!!!

5 Contents 1. Concept - measurement, traceability, uncertainty 2. Uncertainty evaluation 3. Error vs. Uncertainty 4. Uncertainty in multiple measurements

6 measurement in your mind 1. Temperature of this room 2. What time is it now? 3. Concentration of caffeine of this tea 4. Hardness testing 5. IQ (Intellectual Quotient) test 6. Ordering based on children s height. 7. Evaluate the performance of staff members. 8. Evaluate the customer satisfaction of our service. 9. Choosing your job

7 measurement in your mind II 1. Length 2. Height

8 Compilation : What are you going to do?

9 Unit Uncertainty Vocabulary SI 2006 (8 th Ed.) GUM 2008 VIM 2007, 2 nd ed.

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11 Vocabulary Quantity property of a phenomenon, body, or substance, to which a number can be assigned with respect to a reference Value number and reference together expressing magnitude of a quantity Measurand : quantity intended to be measured Measurement process of experimentally obtaining one or more quantity values that can reasonably be attributed to a quantity Measurement result information about the set of quantity values being attributed to a measurand

12 Measurement result uncertainty Value Value and uncertainty Value for regulation Limit of Tolerance

13 Compliance or not 0 10 ppm

14 Zanzibar effect

15 Measurement, traceability and uncertainty Measurement Result (Value and uncertainty) Uncertainty in the value References Measurement Standards (include CRM) Measurement Unknown/Known Known value and its uncertainty ( in Reference) = Uncertainty in comparison Standard Procedure + (ISO Standards) Given uncertainty Measurement Procedure (ISO standards, EPA methods IAEA methods)

16 International Harmonisation Approach 1: Standardization harmonized methods Approach 2: Metrology Metrological traceability Measurement uncertainty prescribed methods/procedures prescribed method-performance characteristics 16

17 Who is going to win in the court?

18 review

19 New need for traceability? Ancient Egypt Modern World Unit: cube meter (SI-System) Primary or Reference Measurement Standard: Working Measurement Standards: Application: granite cube wooden cube manufacture of stone blocks or pieces gauge blocks/laser, Interferometer micrometers, vernier caliper, etc. control of dimensions Recalibration period: each full moon according to frequency of usage Traceability: local International

20 Traceability : after the measurement??? Metrological traceability: VIM 3 (2007) property of measurement result whereby the result can be related reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty Quantity property of a phenomenon, body, or substance, to which a number can be assigned with respect to a reference (VIM3) Role of MS, CRM and MP!!! It is the pre-requisite for your measurement!!!

21 One measurement, Accepted everywhere!!! One standard, One test, Accepted everywhere!!! Worldwide compatibility through worldwide comparability of measurement results. Country A Country C Traceability Industrial work site Calibration CRM Country B Industrial work site Accredited Lab. Accredited Lab ILAC-MRA Industrial work site Accredited Lab. NMI NMI on calibration and testing certificate NMI CIPM-MRA on calibration and measurement certificate

22 KC KCs according to the MRA signed in 1999

23 Gas Measurement 미국 NIST 일본 NMIJ 한국 KRISS 독일 PTB 영국 NPL 국제비교 217 개분야참여 자동차배기가스중일산화탄소농도분석 / 세계최고의측정능력입증 - 이탈리아표준기관 (IEN) 에오존가스표준측정기제작수출 * 국제비교참여실적 (217 건 ) : 세계 6 위

24 Key Comparison, 1 kg

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27 Contents 1. Concept - measurement, traceability, uncertainty 2. Uncertainty evaluation 3. Error vs. Uncertainty 4. Uncertainty in multiple measurements

28 Uncertainty Evaluation Guide to the expression of Uncertainty in Measurement (GUM), 1993, BIPM,IEC,IFCC,ISO, IUPAC, IUPAP, OIML Analyst Sampling Data treatment ability extraction stability experience matrix Temp Reference m. Calibration resolution Assumption Result humidity pressure impurity purity automation drift Laboratory Reagent Instrument Variation of each parameter

29 5 steps in MU evaluation Modeling the measurement y f ( x, x2,..., x 1 n ) Identifying uncertainty components for each input quantity u x i ( ( u u u ( x x x i,1 i,2 i,3 ), ), ),... u s n Evaluating standard uncertainty Type A, Type B u s or s n Sensitivity coefficient Combining standard uncertainties of input quantities u N f ( y i 1 x 2 c ) i 2 u 2 x i k 2 Coverage factor Expanded uncertainty U k u c ( y)

30 Type A evaluation of uncertainty x x i n s n Mean Standard Deviation S.D of the mean s ( xi x) n 1 2 Degree of freedom 3 Standard Uncertainty u i n 1 s n

31 Type B evaluation Previous measurement data Experience with or general knowledge of the behavior and properties of relevant materials and instrument Manufacturer s specifications Data provided in calibration and other certificate Uncertainties assigned to reference data taken from handbooks

32 Traceability of mass The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram. BIPM NMI

33 Uncertainty evaluation Weight using a balance at home, 72.45, 72.54, 72.53, 72.44, 72.39, 72.51, kg Calibration report kg, k 2 1) My weight? 2) Standard uncertainty? 3) Expanded uncertainty?

34 Result y x c u c ( y) u 2 A ( x) u 2 B ( c) Observation Mean Std. Dev Std. Unc Type A evaluation Correction 0.12 Std. Unc k =2 Type B evaluation Result Comb. Std. Unc Ex p. Unc 0.077

35 Value and uncertainty Measurement result can be different.???? Time, method, place, person, procedure

36 Contents 1. Concept - measurement, traceability, uncertainty 2. Uncertainty evaluation 3. Error vs. Uncertainty 4. Uncertainty in multiple measurements

37 Conceptual changes of uncertainty ~ 1984 A measure of the possible error in the estimated value of the measurand as provided by the result of a measurement ~ 1992 An estimate characterizing the range of values with which the true value of a measurand lies (VIM 1) ~ 2007 Parameter associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand (VIM 2) 2008 ~ Parameter that characterizes the dispersion of the quantity value that are being attributed to a measurand, based on the information used. (VIM 3)

38 Reminder GUM E.5.4. While the approach based on true value and error yields the same numerical results as the approach taken in this Guide, this Guide s concept of uncertainty eliminates the confusion between error and uncertainty. Indeed, this Guide s operational approach, wherein the focus is on the observed (or estimated) variability of the value, makes any mention of error entirely unnecessary.

39 Error In general, a measurement has imperfections that give rise to an error in the measurement result. Error = Measurement result True vale True value : value consistent with the definition of a given particular quantity

40 Defining two errors Error 1 = Measurement result True vale True value : value consistent with the definition of a given particular quantity Error 2 = Measured value Reference value Reference value (Assigned value) : The reference quantity value can be a true quantity value of the measurand, in which case measurement error is unknowable, or an appropriate, known quantity value such as a conventional quantity value or a specified target quantity value to be realized in a production process.

41 Error 2 and uncertainty

42 What is your interpretation? The objective of a measurement is to determine the value of the measurand. (GUM, 1993) - True value (error approach) - Measured value (uncertainty approach)

43 Range of true value (limit of error) vs. Uncertainty 1st 2nd

44 Contents 1. Concept - measurement, traceability, uncertainty 2. Uncertainty evaluation 3. Error vs. Uncertainty 4. Uncertainty in multiple measurements (Beyond repeatability conditions and GUM) - Different locations - Different methods - Different instruments

45 Results from different instruments or laboratories

46 Results (mg/kg) Something to remember 7 Diazinon (Day-to-Day Results) Overall 3 2 Day 3 Day 2 Day A-4 A-7 A-14 A-9 A-3 A-12 A-6 A-10 A-5 A-2 A-13 A-8 A-11 A-1 Lab. Code

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48 y x x x u c ( y) u 2 x u( B)

49 Uncertainty for multiple measurements by GUM? JongOh CHOI et al. u y) u ( y) s ( y) / A, P( A w k 1. Uncertainty evaluation for multiple measurements by GUM, Accred. Qual. Assur 8 : 13 (2003) 2. Uncertainty evaluation for multiple measurements by GUM, II Accred. Qual. Assur 8 : 205 (2003) 3. Uncertainty evaluation for multiple measurements by GUM, III Accred. Qual. Assur (2008)

50 Contents 1. Concept - measurement, traceability, uncertainty 2. Uncertainty evaluation 3. Error vs. Uncertainty 4. Uncertainty in multiple measurements

51 This is what you are about to do

52 Make it measurable!! JongOh CHOI kriss.re.kr

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