IEC Guide 115 pdf – Application of uncertainty of measurement to conformity assessment activities in the electrotechnical sector
1Scope
This Guide presents a practical approach to the application of uncertaintyof measurement toconformity assessment activities in the electrotechnical sector. It is specifically conceived foruse in IECEESchemes as well as by testing laboratories engaged in testingelectricalproducts to national safety standards. lt describes the application of uncertaintyofmeasurement principles and provides guidance on making uncertainty of measurementcalculations. lt also gives some examples relating to uncertainty of measurement calculations
for product conformity assessment testing.
2Normative references
The following documents are referred to in the text in such a way that some or all of theircontent constitutes requirements of this document. For dated references,only the editioncited applies. For undated references, the latest edition of the referenced document(including
any amendments) applies.
ISO/IEC 17025,General requirementsfor the competence of testing and calibrationlaboratories
3Terms and definitions
For the purposes of this document, the following terms and definitions apply.
IsO and lEC maintain terminological databases for use in standardization at the followingaddresses:
.IEC Electropedia: available at http://www.electropedia.orgl
.Iso Online browsing platform: available at http://www.iso.orglobp
3.1
coverage factor
number that，when multiplied by the combined standard uncertainty，produces an interval(the expanded uncertainty) about the measurement result that can be expected to encompass
a large，specified fraction (e.g. 95 %) of the distribution of values that could be reasonablyattributed to the measurand
3.2
combined standard uncertainty
result of the combination of standard uncertainty components
3.3
error of measurement
result of a measurement minus a true value of the measurand
Note 1 to entry.: The error of measurement is not precisely quantifiable because the true value lies somewhereunknown within the range of measurement uncertainty.
3.4
expanded uncertainty
value obtained by multiplying the combined standard uncertainty by a coverage factor
3.5
level of confidence
probability that the value of the measurand lies within the quoted range of uncertainty
3.6
measurand
quantity subjected to measurement, evaluated in the state assumed by the measured systemduring the measurement itself
[SOURCE: IEC 60359:2001,3.1.1, modified – The NOTES have been deleted.]
3.7
quantity x
source of uncertainty
3.8
standard deviation
positive square root of the variance
3.9
standard uncertainty
estimated standard deviation
3.10
uncertainty of measurement
parameter,associated with the result of a measurement,that characterizes the dispersion ofthe values that could reasonably be attributed to the measurand
[SOURCE: IEC 60359:2001,3.1.4,modified -The NOTES have been deleted.]
3.11
Type A evaluation method
method of evaluation of uncertainty of measurement by the statistical analysis of a series ofobservations
3.12
Type B evaluation method
method of evaluation of uncertainty of measurement by means other than the statisticalanalysis of a series of observations
4Application of uncertainty of measurement principles
4.1General
4.1.1Qualification and acceptance of Certification Body Testing Laboratories (CBTLs), e.g.in the lECEE,are performed according to lSO/IEC 17025.
4.1.2ISOIEC 17025:2005,5.10.3.1 c) states:
“c) where applicable,a statement on the estimated uncertainty of measurement;information on uncertainty is needed in test reports, when it is relevant to the validity or application of the test results, when a customer’s instruction so requires, or when the uncertainty affectscompliance to a specification limit;””.
ISO/IEC17025:2017,7.8.3.1 c) states:
“c) where applicable，the measurement uncertainty presented in the same unit as that of the measurand or in a term relative to the measurand(e.g. percent) when:
– it is relevant to the validity or application of the test results;
– a customer’s instruction so requires, or
4.1.3 ISO/IEC 17025 was written as a general use document, for all industries. Uncertainty of measurement principles are applied to laboratory testing and presentation of test results to provide a degree of assurance that decisions made about conformance of the products tested according to the relevant requirements are valid. Procedures and techniques for uncertainty of measurement calculations are well established. This document is written to provide more specific guidance on the application of uncertainty of measurement principles to reporting of testing results under the CB Scheme.
4.1.4 Clause 4 of this document focuses on the application of uncertainty of measurement principles under the CB Scheme, while Clause 5 provides guidance on making uncertainty of measurement calculations and includes examples.
4.2 Uncertainty of measurement principles A challenge to applying uncertainty of measurement principles to conformity assessment activities is managing the cost, time and practical aspects of determining the relationships between various sources of uncertainty. Some relationships are either unknown or would take considerable effort, time and cost to establish. There are a number of proven techniques available to address this challenge. These techniques include eliminating from consideration those sources of variability which have little influence on the outcome and minimizing significant sources of variability by controlling them.