IEC 61810-2-2005 pdf – Electromechanical elementary relays – Part 2: Reliability.
3 Terms and definitions For the purposes of this document, the terms and definitions of IEC 60050-1 91 and IEC 60050-444 , some of which are reproduced below, as well as the following, apply. 3.1 item any component that can be individually considered [IEV 1 91 -01 -01 , modified] NOTE For the purpose of this standard, items are elementary relays. 3.2 non-repaired item item which is not repaired after a failure [IEV 1 91 -01 -03, modified] 3.3 cycle operation and subsequent release/reset [IEV 444-02-1 1 ] 3.4 frequency of operation number of cycles per unit of time [IEV 444-02-1 2] 3.5 reliability ability of an item to perform a required function under given conditions for a given number of cycles or time interval [IEV 1 91 -02-06, modified] NOTE 1 It is generally assumed that the item is in a state to perform this required function at the beginning of the time interval. NOTE 2 The term “reliability” is also used as a measure of reliability performance (see IEV 1 91 -1 2-01 ). 3.6 reliability test experiment carried out in order to measure, quantify or classify a reliability measure or property of an item [3.1 .27 of IEC 60300-3-5] 3.7 life test test with the purpose of estimating, verifying or comparing the lifetime of the class of items being tested [3.1 .1 7 of IEC 60300-3-5]
4 General considerations The provisions of this part of IEC 61 81 0 are based on the relevant publications on dependability. In particular, the following documents have been taken into account: IEC 60050-1 91 , IEC 60300-3-5 and IEC 61 649. The aim of reliability testing as given in this standard is to obtain objective and reproducible data on reliability performance of elementary relays representative of standard production quality. The tests described and the related statistical tools to gain reliability measures based on the test results can be used for the estimation of such reliability measures, as well as for the verification of stated measures. According to Clauses 8 and 9 of IEC 60300-3-5, for non-repaired items showing a non- constant failure rate the Weibull model is the most appropriate statistical tool for evaluation of reliability measures. This analysis procedure is described in IEC 61 649. Elementary relays within the scope of this standard are considered as non-repaired items. They generally do not exhibit a constant failure rate but a failure rate increasing with time, being tested until wear-out mechanisms become predominant. The cycles to failure of a random sample of tested items typically show the Weibull distribution. The statistical procedures of this standard are valid only when at least 1 0 relevant failures are recorded.
The first step in the analysis of the recorded cycles to failure (CTF) of the tested relays is the determination of the two distribution parameters of the Weibull distribution. In a second step, the mean cycles to failure (MCTF) is calculated as a point estimate. In a third step, the useful life is determined as the lower confidence limit of the number of cycles by which 1 0 % of the relay population will have failed (B 1 0 ). With a given frequency of operation these reliability measures expressed in number of cycles (MCTF) can be transformed into respective times (MTTF), see Annex C for an example. The statistical procedures require some appropriate computing facility. Software for evaluation of Weibull distributed data is commercially available on the market. Such software may be used for the purpose of this standard provided it shows equivalent results when the data given in Annex C are used. Since the number of cycles to failure highly depends on the specific set of test conditions (particularly the electrical loading of the relay contacts), values for MCTF and useful life derived from test data apply only to this set of test conditions, which have to be stated by the manufacturer together with the reliability measures.
5 Test conditions 5.1 Test items As a minimum of 1 0 failures need to be recorded to perform the analysis described in this standard, 1 0 or more items (relays) should be submitted to the test. This allows the test to be truncated when at least 1 0 relays have failed. The items shall be selected at random from the same production lot and shall be of identical type and construction. No action is allowed on the test items from the time of sampling until the test starts. Where any particular burn-in procedure or reliability stress screening is employed by the manufacturer prior to sampling, this shall apply to all production. The manufacturer shall describe and declare such procedures, together with the test results. Unless otherwise specified by the manufacturer, all contacts of each relay under test shall be loaded as stated and monitored continuously during the test. The test starts with all items and is stopped after a certain number of cycles. At that instant a certain number of items (minimum: 1 0 items) have failed. The number of cycles to failure of each of the failed items is recorded.