BS EN 61703-2016 pdf free download.Mathematical expressions for reliability, availability, maintainability and maintenance support terms
This International Standard provides mathematical expressions for selected reliability,availability, maintainability and maintenance support measures defined in IEC 60050-1 92:201 5. In addition, it introduces some terms not covered in IEC 60050-1 92:201 5. They are related to aspects of the system of item classes (see hereafter).
According to IEC 60050-1 92:201 5, dependability [1 92-01 -22] is the ability of an item to perform as and when required and an item [1 92-01 -01 ] can be an individual part, component,device, functional unit, equipment, subsystem, or system.
To account for mathematical constraints, this standard splits the items between the individual items considered as a whole (e.g. individual components) and the systems made of several individual items. It provides general considerations for the mathematical expressions for systems as well as individual items but the individual items which are easier to model are analysed in more detail with regards to their repair aspects.
The following item classes are considered separately:
• Systems;
• Individual items:
– non-repairable [1 92-01 -1 2];
– repairable [1 92-01 -1 1 ]:
i) with zero (or negligible) time to restoration;
ii) with non-zero time to restoration.
In order to explain the dependability concepts which can be difficult to understand, keep the standard self-contained and the mathematical formulae as simple as possible, the following basic mathematical models are used in this standard to quantify dependability measures:
• Systems:
– state-transition models;
– Markovian models.
• Individual items:
– random variable (time to failure) for non-repairable items;
– simple (ordinary) renewal process for repairable items with zero time to restoration;
– simple (ordinary) alternating renewal process for repairable items with non-zero time to restoration.
The application of each dependability measure is illustrated by means of simple examples.
This standard is mainly applicable to hardware dependability, but many terms and their definitions may be applied to items containing software.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60050-1 92:201 5, International electrotechnical vocabulary – Part 1 92: Dependability (available at http://www.electropedia.org)
ISO 3534-1 :2006, Statistics – Vocabulary and symbols – Part 1 : General statistical terms and terms used in probability
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-1 92:201 5,ISO 3534-1 and the following apply.
NOTE To facilitate the location of the full definition, the IEC 60050-1 92 reference for each term is shown [in square brackets] immediately following each term, for example:
mean time to restoration [1 92-07-23]
The terms and definitions given in Clause 3, which do not appear in IEC 60050-1 92, are used in order to facilitate the presentation of mathematical expressions of some IEC 60050-1 92 terms. Some terms have been taken from IEC 60050-1 92 and modified for the needs of this standard.
3.1 instantaneous restoration intensity
restoration intensity restoration frequency
limit, if it exists, of the quotient of the mean number of restorations [1 92-06-23] of a repairable item [1 92-01 -1 1 ] within time interval [t, t + ∆t], and ∆t, when ∆t tends to zero, given that the item is as good as new at t = 0
( = E N R (t + Δt) − N R (t) | as good as new at t = 0
N R (t) is the number of restorations in the time interval [0, t];
E denotes the expectation.
Note 1 to entry: The difference between the restoration intensity and the repair rate comes from the conditions:the item is as good as new at time t = 0 for the restoration intensity and for the repair rate the repair starts at time t = 0. From a mathematical point of view, the restoration intensity is similar to the unconditional failure intensity (see 3.8).
Note 2 to entry: The unit of measurement of instantaneous restoration intensity is the unit of time to the power-1 .
3.2 instantaneous repair rate
repair rate µ(t)
limit, if it exists, of the quotient of the conditional probability that the repair is completed within time interval [t, t + ∆t] and ∆t, when ∆t tends to zero, given that the repair started at t = 0 and had not been completed before time t.BS EN 61703 pdf download.