IEC 61650:1997 pdf download – Reliability data analysis techniques – Procedures for comparison of two constant failure rates and two constant failure (event) intensities.
— failure rates;
— failure intensities:
ratesiintensities of relevant events.
The procedures are used to determine whether an apparent difference between the two sets of observations can be considered statistically significant
It is assumed that the time intervals tobetween the failures (events) are independent and identically exponentially distributed during the observation period (that is. the accumulated relevant test time).
NOTE — This assumption implies thai h• lailuri rat.rlt.nsily is constant
It is furthermore assumed that there are technical or other reasons to believe that a difference (either an improvement or deterioration) might exist between the observed reliability characteristic of the two sets of items under comparison. Some examples of typical applications are described in 5.4.
The methods are designed as hypothesis tests which state, with a specified risk (the significance level), whether the two series of observations belong to the same population or the same process, that is they have the same true mean value.
NOTE — Faifure rate. whicS Is relevant to non-repaired ItemS, IS associated wim a distreullon of times to failure. Failure Intensity. which Is relevant to repaired items only. is associated with a point process descnb.n9 a sequence of events. for example time. between failures on a lime &xis.
The procedures are not restricted to comparison of failure rateintensity, but can be applied to observations of two series of any relevant events, provided the above assumptions are valid.
NOTE — The two series of obServations may be of items from the same population, or the same item under different conditions (for example environment amid load), or just comparable series of events (lot example car accidwits on a road)
Numerical methods and a graphical procedure are prescribed. The observation periods relevant to the two series do not need to be equal, but if they are, the methods are very simple.
5 Assumptions and area 01 application
5.1 Assumptionsi
The tests are based on the assumption that the time intervals tobetween the failures are independent and identically exponentially distnbuted during the observation period (accumulated relevant test time) This assumption implies constant failure rate and constant failure intensity. respectively.
Because it is assumed that there are technical or other reasons to believe that a difference (either an improvement or deterioration) might exist between the observed reliability characteristics of the two sets of items or observations under comparison, the one-sided test procedures indicated are valid.
52 Repaired items
The procedures are applicable for comparing observations of failure intensity (as derived from repaired items), provided that within each period the following assumptions are true:
— the accumulated relevant test time is calculated as elapsed operating time (excluding repair times and other down times), see figure 1;
— the repaired items can be considered “as good as new’.
IEC 61650:1997 pdf download – Reliability data analysis techniques – Procedures for comparison of two constant failure rates and two constant failure (event) intensities
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