WG 2 - TC 56/WG 2

IEC 61123:2019 is intended to define a procedure to verify if a reliability of an item/system complies with the stated requirements. The requirement is assumed to be specified as the percentage of success (success ratio) or the percentage of failures (failure ratio). This document can be used where a number of items are tested (number of trials performed) and classified as passed or failed. It can also be used where one or a number of items are tested repeatedly. The procedures are based on the assumption that the probability of success or failure is the same from trial to trial (statistically independent events). Plans for fixed trial/failure terminated tests as well as truncated sequential probability ratio tests (SPRTs) are included. This document contains extensive tables with ready-to-use SPRT plans and their characteristics for equal and non-equal risks for supplier and customer. In the case of the reliability compliance tests for constant failure rate/intensity, IEC 61124 applies. This second edition cancels and replaces the first edition published in 1991. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
The sequential probability ratio test (SPRT) [1, 2][1] has been significantly developed in recent years [3, 4, 5]. This edition contains shorter and accurate tests, a wide range of test plans, and significant additional characteristic data, as follows:
the tests are significantly truncated (the maximum trial numbers are low) without substantially increasing the expected number of trials to decision (ENT);
the true producer’s and consumer’s risks (α', β') are given and very close to the nominal (α, β);
the range of the test parameters is wide (failure ratio, risks and discrimination ratio);
the test plans include various risk ratios (not restricted to equal risks only);
the values of ENT are accurate and given in the relevant region (for practical use);
guidelines for extension of the test sets (interpolation and extrapolation) are included.
In Annex C, the use of the cumulative binomial distribution function of Excel that simplifies the procedure of designing has been added (Clause C.3).
Keywords: verify if a reliability of an item/system complies with the stated requirements

IEC 61078:2016 this International Standard describes:
- the requirements to apply when reliability block diagrams (RBDs) are used in dependability analysis;
- the procedures for modelling the dependability of a system with reliability block diagrams;
- how to use RBDs for qualitative and quantitative analysis;
- the procedures for using the RBD model to calculate availability, failure frequency and reliability measures for different types of systems with constant (or time dependent) probabilities of blocks success/failure, and for non-repaired blocks or repaired blocks;
- some theoretical aspects and limitations in performing calculations for availability, failure frequency and reliability measures;
- the relationships with fault tree analysis (see IEC 61025) and Markov techniques (see IEC 61165). This third edition cancels and replaces the second edition published in 2006. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- the structure of the document has been entirely reconsidered, the title modified and the content extended and improved to provide more information about availability, reliability and failure frequency calculations;
- Clause 3 has been extended and clauses have been introduced to describe the electrical analogy, the "non-coherent" RBDs and the "dynamic" RBDs;
- Annex B about Boolean algebra methods has been extended;
- Annex C (Calculations of time dependent probabilities), Annex D (Importance factors), Annex E (RBD driven Petri net models) and Annex F (Numerical examples and curves) have been introduced. Keywords: reliability block diagram (RBD)

IEC 62506:2013 provides guidance on the application of various accelerated test techniques for measurement or improvement of product reliability. Identification of potential failure modes that could be experienced in the use of a product/item and their mitigation is instrumental to ensure dependability of an item. The object of the methods is to either identify potential design weakness or provide information on item dependability, or to achieve necessary reliability/availability improvement, all within a compressed or accelerated period of time. This standard addresses accelerated testing of non-repairable and repairable systems. It can be used for probability ratio sequential tests, fixed duration tests and reliability improvement/growth tests, where the measure of reliability may differ from the standard probability of failure occurrence. This standard also extends to present accelerated testing or production screening methods that would identify weakness introduced into the product by manufacturing error, which could compromise product dependability. Keywords: test techniques for measurement or improvement of product reliability

IEC 61710:2013 specifies procedures to estimate the parameters of the power law model, to provide confidence intervals for the failure intensity, to provide prediction intervals for the times to future failures, and to test the goodness-of-fit of the power law model to data from repairable items. It is assumed that the time to failure data have been collected from an item, or some identical items operating under the same conditions (e.g. environment and load). This second edition cancels and replaces the first edition, published in 2000, and constitutes a technical revision. The main changes with respect to the previous edition are listed below: the inclusion of an additional Annex C on Bayesian estimation for the power law model. Keywords: power law model, Bayesian estimation, reliability of repairable items

IEC 61709:2011 gives guidance on how failure rate data can be employed for reliability prediction of electric components in equipment. Reference conditions are numerical values of stresses that are typically observed by components in the majority of applications. Reference conditions are useful since they are the basis of the calculation of failure rate under any conditions by the application of stress models that take into account the actual operating conditions. This standard also gives guidance on how a database of component failure data can be constructed to provide failure rates that can be used with the included stress models. This edition includes the following significant technical changes with respect to the previous edition:
- the addition of a number of component types and the updating of models for a large number of component types;
- the addition of annexes on reliability prediction, sources of failure rate data and component classification information.

This part of IEC 61163 describes particular methods to apply and optimize reliability stress screening processes for lots of repairable hardware assemblies, in cases where the assemblies have an unacceptably low reliability in the early failure period, and when other methods, such as reliability growth programmes and quality control techniques, are not applicable.

Provides statistical methods for evaluating point estimates, confidence intervals, prediction intervals and tolerance intervals for the failure rate of items whose time to failure follows an exponential distribution.

Provides guidelines for the planning and performing of reliability tests and the use of statistical methods to analyse test data. Describes the tests related to repaired and non-repaired items together with tests for constant and non-constant failure intensity and constant and non-constant failure rate. The purpose of these tests is to discover weaknesses in the design and to undertake actions to eliminate these weaknesses and thereby improve performance, quality, safety, robustness, reliability and availability and reduce costs.