TS EN 61078

TS EN 61078 is the standard for reliability block diagrams (RBDs) and their use in dependability analysis. It focuses on how to represent a system as a logic-based arrangement of blocks whose successful operation is needed for the system to perform its intended function, and how to evaluate system-level dependability from that model. In practice, RBDs are widely used to understand how component arrangement, redundancy, and dependency structure influence overall reliability.

What reliability block diagrams represent

In general technical terms, an RBD is a graphical model of functional success paths. It does not describe every physical detail of a system; instead, it captures the logical conditions under which the system works. That makes it especially useful for comparing series structures, parallel redundancy, and more complex configurations. By reducing a system to functional blocks and success relationships, engineers can see which subsystems are critical to mission success and where redundancy improves resilience.

Analytical coverage of the standard

According to the supplied scope, this standard sets out requirements for using RBDs in dependability analysis and procedures for modelling system dependability with reliability block diagrams. It also covers how RBDs are used for qualitative and quantitative analysis, including the calculation of availability, failure frequency, and reliability measures for different system types with constant or time-dependent block success/failure probabilities, and for both non-repaired and repaired blocks. The standard further addresses theoretical limitations in these calculations and the relationship of RBD methods with fault tree analysis and Markov techniques.

The revised edition expands the framework with additional discussion of the electrical analogy, non-coherent RBDs, and dynamic RBDs. More broadly, this makes the standard useful for engineers and analysts who need a structured way to translate system architecture into reliability metrics and to compare modelling approaches within dependability engineering.

• Logical modelling of system success through block interconnections
• Procedures for qualitative and quantitative dependability analysis
• Calculation of availability, failure frequency, and reliability measures
• Use with non-repaired and repaired blocks
• Connections to fault tree analysis and Markov techniques