Reliability Block Diagramming (RBD)
DEFINITION
Reliability Block Diagrams (RBD’s) establish system reliability on a modular/block basis rather than a component basis using a block diagram approach.
SITUATION
For complex systems, RBD’s make the reliability of a system much easier to understand, expose weaknesses much quicker, and make what-if analyses much easier.
OBJECTIVES
To develop a reliability model using blocks or modules to make the model easier to understand and change.
VALUE TO YOUR ORGANIZATION
Used early in a design cycle, it allocates reliability among blocks, guiding architecture and design decisions to achieve an overall system reliability requirement.
Used on established designs, it sorts every component into blocks according to their function to expose the distribution of failure rates.
RELIABILITY INTEGRATION
An example of Reliability Integration during Reliability Block Diagramming (RBD) is as follows:
Information from Reliability Block Diagrams feed directly into design decisions
If the block diagram concludes that the only way to meet the design goal is to add redundancy, then this becomes input to the design early on so that cost and schedule impacts are kept to a minimum.
METHODOLOGY
We start out with a high level BOM or functional block diagram and from that, we establish redundancy paths and assign an MTBF to each block. We make this assignment from vendor data, past products, benchmarking, and a variety of other means. Then we calculate the total system reliability based on each block.
CASE STUDIES/OPTIONS
The following case studies and options provide example approaches. We shall tailor our approach to meet your specific situation.
-
RDB’s Make Understanding Reliability of Complex Systems Easier
For a Networking company with a highly complex core switch, we developed a reliability block diagram to make the reliability of the system easier to understand.
-
Using RDB’s to Help Drive Design Decisions
A Medical Device company had a system comprised of many blocks. We developed a Reliability Block diagram to help them understand the driving forces of reliability early in a design effort and created a functional block diagram to determine where to concentrate design efforts.
-
Using RDB’s to Drive Redundancy Decisions
A Military contractor had a specific reliability goal in mind and had a choice of using redundancies but needed to make this decision very early in the design process. We developed a Reliability Block Diagram for them and showed them where they could take advantage of redundancies to meet their goals.
