Why is knowledge on measurement uncertainty so important in setting policies on energy efficiency? Rainer Stamminger & Christoforos Spiliotopoulos

Transcription

1 Why is knowledge on measurement uncertainty so important in setting policies on energy efficiency? Rainer Stamminger & Christoforos Spiliotopoulos

2 Agenda What is the problem? Differentiating targets Sources of uncertainties Uncertainty of measurements Conflicts What is the solution? Summary EEDAL 2017 R. Stamminger & C. Spiliotopoulos 2

3 What is the problem? Why do we need a low uncertainty? Because we want to differentiate between two targets! High uncertainty Bad differentiation between targets Low uncertainty Good differentiation between targets Low uncertainty High level of differentiation EEDAL 2017 R. Stamminger & C. Spiliotopoulos 3

4 What is the problem? Precision and accuracy of the measurement! Accuracy low high low uncertainty High uncertainty low high Precision EEDAL 2017 R. Stamminger & C. Spiliotopoulos 4

5 What is the problem? 1. All measurements have uncertainties Three different causes of uncertainties: (1) manufacturing variation (2) measurement uncertainty (3) reproducibility of measurement 2. Uncertainties of measurements should be known when measurement standards are used for comparative or regulatory purposes (manufacturing tolerances may/ should be outside of the assessment of the measurement uncertainty) 3. Verification tolerances (e.g. in ecodesign and labelling directives) should be based on the uncertainties of the measurement. EEDAL 2017 R. Stamminger & C. Spiliotopoulos 5

6 Sources of uncertainties Sources of uncertainties: a) incomplete definition of the measurand; b) imperfect reaiisation of the definition of the measurand; c) non-representative sampling the sample measured may not represent the defined measurand; d) inadequate knowledge of the effects of environmental conditions on the measurement or imperfect measurement of environmental conditions; e) personal bias in reading analogue instruments; f) finite instrument resolution or discrimination threshold; g) inexact values of measurement standards and reference materials; h) inexact values of constants and other parameters obtained from external sources and used in the data-reduction algorithm; i) approximations and assumptions incorporated in the measurement method and procedure; j) variations in repeated observations of the measurand under apparently identical conditions. (cited from GUM, 3.3.2) EEDAL 2017 R. Stamminger & C. Spiliotopoulos 6 Many sources of uncertainties

7 Terms relevant Declaration is a statement of the producer / importer on the performance of a product following the requirements (of the EU regulation). Verification is conformity assessment of the declaration performed by market surveillance authorities (MSA) Verification tolerance is the permitted range of variation that the value of a parameter measured by MSA during a product verification procedure may have Repeatability standard deviation: standard deviation of test results or measurement results obtained under repeatability conditions Reproducibility standard deviation: standard deviation of test results or measurement results obtained under reproducibility conditions. Repeatability conditions Reproducibility conditions Test items identical Laboratory same different Operator same different Equipment same different Uncertainty result Repeatability standard deviation Reproducibility standard deviation R. Stamminger & C. Spiliotopoulos but complying with the same measurement standard!

8 Uncertainty of measurements measured value Uncertainty problems: 1. Normally, just one result is available, but it may be anywhere in the range of the probability distribution 2. Other labs may have some systematic difference in their measurements although done under reproducability conditions 3. It is important to know the overall uncertainty Probability distribution Lab A overall uncertainty = reproducibility distribution Lab B Lab C Lab D Lab E many labs EEDAL 2017 R. Stamminger & C. Spiliotopoulos 8

9 Uncertainty of measurements measured value Limit (ecodesign or class border) Lab A Lab B Lab C Lab D Lab E many labs EEDAL 2017 R. Stamminger & C. Spiliotopoulos 9

10 Uncertainty of measurements measured value Tolerance in verification procedure Limit? Lab A Lab B Lab C Lab D Lab E many labs EEDAL 2017 R. Stamminger & C. Spiliotopoulos 10

11 Uncertainty of measurements Tolerance too large: Cheating possible! Overall uncertainty gives the appropriate information on how accurate a measurement may be when done in Tolerance too small! different laboratories Consequence: - False measurement of non-compliance possible measured value Tolerance in verification procedure? overall uncertainty = reproducibility distribution Lab A Lab B Lab C Lab D Lab E many labs EEDAL 2017 R. Stamminger & C. Spiliotopoulos 11

12 measured value Limit Uncertainty of measurements Declaration problems: 1. It is normally not predictable where my own lab is in the field of laboratories 2. Also my lab result has uncertainty. 3. Verification may take place in any other laboratory 4. Knowledge on overall uncertainty may help to assess the risk of being measured within the forbidden limit area at a given declaration Tolerance in verification procedure overall uncertainty = reproducibility distribution Lab A Lab B Lab C Lab D Lab E many labs EEDAL 2017 R. Stamminger & C. Spiliotopoulos 12

13 Aspects of testing! Production variation Declaration Measurement uncertainty Qualified laboratory Verification Verification tolerance EEDAL 2017 R. Stamminger & C. Spiliotopoulos 13

14 What is the solution? 1. Uncertainties of the measurements in the standards must be known and reported not only of the measurement instrument, but the complete measurement set-up taking into account real data e.g. gathered by round-robin-tests (IEC TR 62970), assessing the reproducibility examples: For laundry appliances: see IEC TR For other appliances:??? EEDAL 2017 R. Stamminger & C. Spiliotopoulos 14

15 What is the solution? 2. based on sound statistical analysis, following established standards (e.g. IEC Guide 115, ISO/IEC Guide 98-1, ISO 5725 or simplified approaches like IEC TR 61923) using as common approach: expanded uncertainty, meaning a product re-measured in any laboratory will find a value within this range with 95 % probability ±2σ overall uncertainty distribution (if normal distribution is assumed) Measurand Expanded uncertainty := 2 * reproducibility standard deviation EEDAL 2017 R. Stamminger & C. Spiliotopoulos 15

16 Summary Uncertainties in measurements are unavoidable Regulations (and declarations) need to consider those uncertainties Measurement uncertainties are to be separated from circumvention and defeat devices A common way to express measurement uncertainties is to use expanded uncertainties EEDAL 2017 R. Stamminger & C. Spiliotopoulos 16

17 Thank you for joining! Thank you for the attention! Contact: Prof. Dr. Rainer Stamminger University of Bonn Institute of Agricultural Engineering Nussallee Bonn/ Germany phone: stamminger@uni-bonn.de