RAMS Definitions

RAMS definitions

Reliability •

The ability of a system or component to perform its required functions under stated conditions for a specified period of time. It is often reported in terms of a probability. (wiki - common defenition)

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Continuity of correct service (as an attribute of dependability theory) The probability of successful operation or performance of systems and related equipment, with minimal risk of loss or disaster or of system failure. Designing for reliabilty requires an evaluation of the effects of failure of the inherent systems and equipment (as a part of Engineering Integrity and RAMS analyses)

Availability •

The degree to which a system, subsystem, or equipment is operable and in a committable state (wiki)

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Readiness for correct service (as an attribute of dependability theory) That aspect of system reliability that takes equipment maintainability into account. Design for availability requires an evaluation of the consequences of unsuccessful operation or performance of the integrated systems, and the critical requirements necessary to restore operation or performance to design expectations (as a part of Engineering Integrity and RAMS analyses)

Maintainability •

In software engineering, the ease with which a software product can be modified in order to: correct defects, meet new requirements, make future maintenance easier, or cope with a changed environment (wiki)

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ability to undergo, modifications, and repairs (as an attribute of dependability theory)

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that aspect of maintenance that takes downtime of the systems into account. Designing for maintainability requires an evaluation of the accessibility and repairability of the inherent systems and their related equipment in the event of failure, as well as of integrated systems shutdown during planned maintenance (as a part of Engineering Integrity and RAMS analyses)

Safety •

Safety is often seen as one of a group of related disciplines: quality, reliability, availability, maintainability and safety (wiki, system safety)

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absence of catastrophic consequences on the user(s) and the environment (as an attribute of dependability theory)

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thee categories: personal protection, equipment protection, environmental protection. Means “not involving risk”, where the risk is “the chance of loss or disaster”. Designing for safety is inherent in the development of designing for reliability and maintainability of systems and their related equipment.

Reliability - The probability of successful operation or performance of systems and related equipment, with minimal risk of loss or disaster or of system failure MTTF (Mean Time To Failure) - The arithmetic mean (average) time to failures of a system Failure rate - is the frequency with which an engineered system or component fails, expressed for example in failures per hour.

Maintainability - Ability to undergo, modifications, and repairs MTTR (Mean Time To Repair) - The average time that a device will take to recover from any failure

Availability (A) - Readiness for correct service A=MTTF/(MTTF+MTTR)

Safety (S) - Absence of catastrophic consequences on the user(s) and the environment Hazard - A condition or situation that exists within the working environment capable of causing harm, injury, and/or damage. Hazard severity (HS) - A categorical description of hazard level based on real or perceived potential for causing harm, injury, and/or damage. Hazard probability (HP) - The likelihood that a condition or set of conditions will exist in a given situation or operating environment. S=HSxHP

HW

SW

HW component RAMS assessment MTTR tables

MTTF tables

Look at MTTR table

MTTR tests

MTTR

Look at MTTF table

MTTF tests

Look at hazard table

MTTF

S= HS*FailureRate

A = MTTF/ (MTTF+MTTR)

M

Hazard severity tables

existed HW component

A

R

S

HW system RAMS assessment MTTR tables

MTTF tables

Look at MTTR table

Hazard severity tables

HW system design level

Look at hazard table

Look at MTTF table

MTTRs

Severities MTTFs

Maintainability analysis

M

FTA, RBD, CTMC. SGPN, SPA

A

FTA, RBD, CTMC. SGPN, SPA

R

FTA, RBD, CTMC. SGPN, SPA

S