What is BS EN IEC 61123 about?
BS EN IEC 61123 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).
BS EN IEC 61123 can be used where a number of items are tested (number of trials performed) and classified as passed or failed. BS EN IEC 61123 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. BS EN IEC 61123 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.
Who is BS EN IEC 61123 for?
BS EN IEC 61123 on reliability testing is useful for:
- Reliability testers
- Product testing facilities
- Regulatory authorities
Why should you use BS EN IEC 61123?
A compliance test is an essential part of the reliability assurance system. Reliability is affected by many random factors, so its prediction is not accurate. The direct way to check if the item/system meets its reliability specifications is to perform a compliance test.
BS EN IEC 61123 is dedicated to sampling plans for the tests.
BS EN IEC 61123 contains two types of tests truncated sequential probability ratio test (SPRT) and fixed trial/failure terminated test (FTFT).
The fixed trial/failure terminated test (FTFT) given in BS EN IEC 61123 is characterized by decision rules for accepting or rejecting compliance when the termination trials number nf (MaxNT) has been reached, or the acceptable number of failures c has been exceeded. This test has the smallest nf among all tests with specified PRP and CRP. When testing objects with p ≤ p0, ENT is close to nf, and for p > p0, ENT decreases significantly. Another advantage of the FTFT is the ability to conduct all trials simultaneously, but ENT increases and becomes equal to nf.
BS EN IEC 61123 provides the truncated sequential probability ratio test (SPRT), in which the decision is made after each trial: accept or reject compliance, or continue testing. BS EN IEC 61123 contains a truncated SPRT with MaxNT = nt. This nt is 1,1 to 1,2 times greater than nf of the FTFT with the same PRP and CRP. However, the ENT of the SPRT is significantly smaller than that of the corresponding FTFT, and for p ≤ p0 it can be 1,4 to 1,8 times smaller. This is a great advantage of the SPRT.
The planning of the SPRT is quite complicated so BS EN IEC 61123 contains extensive tables with ready-to-use test plans and their characteristics. Tests are listed for α = β as well as for α ≠ β .
The tables also allow the design of additional tests by simple interpolation and, for small p0, by extrapolation.
The data in BS EN IEC 61123 allows you to assess the economic benefit of the OC test requirements and, in general, to assess the advisability of performing the test.
What’s changed since the last update?
BS EN IEC 61123:2020 is the second edition that replaces the first edition published in 1991. BS EN IEC 61123:2020 constitutes a technical revision.
BS EN IEC 61123:2020 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).