What is IEC 61078?

IEC 61078, titled “Reliability block diagrams”, is the international standard that defines the RBD technique: how to represent a system as a network of blocks and how to evaluate its reliability and availability from the reliability of its parts. The current edition is IEC 61078:2016 (third edition) — always check for the latest edition for contractual work.

The standard sets out, in essence:

• The representation — how to draw a system as a reliability block diagram, where a path of working blocks from input to output means the system succeeds.
• The structures — series (all required), parallel and k-of-n redundancy, and combinations of them.
• The evaluation methods — how to compute system reliability/availability from block values, both by Boolean / analytical techniques and, where the structure or time-dependence makes closed-form maths impractical, by simulation.

IEC 61078 is the methodological backbone of RBD-based RAM analysis. Building your model to a recognised standard means the structure of the analysis — what counts as success, how redundancy is treated — follows an internationally agreed method rather than an ad-hoc convention, which matters when a study is reviewed or audited.

It is one of several references behind a RAM study; see the wider list in the standards section of the guide, and the production-assurance framework in ISO 20815.

Ramly implements the RBD technique of IEC 61078 — series, parallel (k-of-n) and standby structures, nested to any depth — and evaluates it by Monte Carlo simulation. Simulation is the route the standard points to when a model includes the things closed-form maths can’t easily handle: repair, preventive maintenance, limited spares and crews, and ageing equipment.