Measurement & Uncertainty - Concept and its application

Transcription

1 Measurement & Uncertainty - Concept and its application June JongOh Choi (choijongoh@kriss.re.kr)

2 I don t know what I don t know. If we don t express what we know in the form of numbers, we really don t know much about it. If we don t know much about it, we can t control it. If we can t control it, we are at the mercy of chance.

3 Make it measurable!!! Head, Center of Standards and Quality management Chair, Uncertainty committee of KRISS Very Practical Philosopher on Measurement Education Ph. D. Analytical Chemistry, (1992) M. Eng. Chemical Engineering, (1983) B. Eng. Chemical Engineering, (1981) Field of Interest - Quality of Management (2005 -) - Uncertainty in Measurement (2003 -) - Reliability of Chemical measurement (National Research Laboratory 1999) - Analytical chemistry To be your Choice in Measurement More than 270 Lectures on Measurement & Uncertainty, Reference Materials, PT, QMS, Standards etc

4 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

5 What are you going to do?

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

7 Unit Uncertainty Vocabulary SI 2006 (8 th Ed.) GUM 2008, 1993 VIM 2007, 2 nd ed.

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9 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 or partner

10 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

11 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)

12 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.

13 Obtained from a training course on uncertainty?

14 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

15 Error 1

16 Measurement result uncertainty Value Value and uncertainty (k=2, 95 %, level of confidence) Value for regulation Limit of Tolerance

17 Driver Under Influence with uncertainty

18 DUI I : Proper accusation? % the uncertainty is %.

19 DUI II : % No more false accusation? %

20 DUI III U = 2 u? U = 3 u % %

21 DUI IV? U = 3 u? % % the uncertainty is %.

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

23 Zanzibar effect

24 Measurement, traceability and uncertainty Measurement Result (Value and uncertainty) Uncertainty in the value = Measurement Unknown/Known Uncertainty in comparison References Measurement Standards (include CRM) Known value and its uncertainty ( in Reference) + Given uncertainty

25 Review

26 Error 2 and uncertainty

27 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.

28 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)

29 International Harmonisation Approach 1: Standardization harmonized methods Approach 2: Metrology Metrological traceability Measurement uncertainty prescribed methods/procedures prescribed method-performance characteristics 29

30 Who is going to win in the court?

31 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

32 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

33 Review 1. Measurement process of experimentally obtaining one or more quantity values that can reasonably be attributed to a quantity 2. Traceability property of a measurement result whereby the result can be related to a stated metrological reference through a documented unbroken chain of calibrations of measuring systems, each contributing to the measurement uncertainty 3. Measurement uncertainty Parameter that characterizes the dispersion of the quantity values that are being attributed to a measurand, based on the information used. (VIM 3, 2007)

34 Conceptual changes of uncertainty Classical approach ~ 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) Uncertainty approach ~ 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)

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

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

37 Results from different instruments or laboratories

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

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

41 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)

42 Measurement vs. Evaluation 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 or partner

43 Please do not torture the data until it confess!! JongOh CHOI kriss.re.kr

44 PDB05014 Please don t torture the data!!!! Metrologists set up a measurement model, then improve it, if necessary. On the contrary, statisticians use the measured values to set up a statistical model, then explain the measurement results. We should take a KCRV as a result of collaborative measurement (to achieve compatible results), rather than of statistical treatments (for the explanation of errors). Source: JongOh Choi, BIPM-NMIJ-KCRV Workshop TOKYO P De Bièvre BIPM NMU Symposium TSUKUBA

45 No argument on measurement results!!!

46 This is what you are about to do

47 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)

48 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

49 KC KCs according to the MRA signed in 1999

50 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

51 Key Comparison, 1 kg

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54 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

55 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)

56 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

57 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

58 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?

59 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

60 Argon concentration measurements in dry air. Year Author Method of measurements Argon concentration in dry air (mmol/mol) 1895 Rayleigh and Ramsey chemical Schloesing chemical 9.35 (0.02) 1895 Kellas chemical Moissan chemical 9.34 (0.02) 1911 Moureu and Lepape chemical Cady and Cady chemical 9.35 (0.1) 1949 Chackett et al. chemical 9.17 (0.04) 1957 Oana chemical 9.17 (0.07) 1969 Hughes Mass spectrometry 9.16 (0.10) 2004 Park and Kim Mass spectrometry (0.003)

61 Compliance or not 0 10 ppm