RAMS (Reliability, Availability, Maintainability and Safety) analyses are essential components of critical systems design and management. Neglecting RAMS during design can result in expensive failures, redesigns, and safety events. Furthermore, RAMS analyses are required by standards and regulations in industries such as rail, aerospace, medical, defense and nuclear.
Typical RAMS tasks include:
- Identify and mitigate risk due to equipment failure modes
- Design of Safety Related Systems (SRS)
- Redundancy / Fault Tolerance: how many standby units to hold, and operation profile (warm or cold)
- Design of efficient Built In Test (BIT) plan for high coverage and failure isolation
- Design system to be easily and quickly maintained
- Achieve high system availability
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- FMEA / FMECA (Failure Modes, Effects, and Criticality Analysis) flexible module supporting all major safety standards: Mil-Std-1629A, Mil-Std-882E, ISO 31000, IEC 61508, AIAG FMEA-4, and SAE J1739.
- FTA (Fault Tree Analysis) for calculating Mission Reliability. Complies with IEC 61025.
- Testability Analysis for design of Built In Tests (BITs) with high failure mode coverage and Isolation. Complies with MIL-STD 2165.
- Reliability Block Diagram including Safety Integrity Level (SIL) analysis, RBD Networks and Markov chain models. Complies with IEC 61078 and IEC 61508.
- Statistical analysis of failure and maintenance field data. Complies with MIL HDBK 338A.
Standard Reliability Analysis process
Terminology
Reliability is defined as the probability that an item will perform a defined function without failure under stated conditions, for a stated period of time.
Availability is basically defined as:
Ao = MTBF/(MTBF+MTTR)
MTBF = Mean Time Between Failures
MTTR = Mean Time To Repair (or Replace)
Many variants of availability definitions exist depending on maintenance, inspections and logistic time.