Reliability Block Diagrams (RBD)

Background

A Reliability Block Diagram (RBD) is a graphical schematic of the dependencies between

items in a system model. The purpose of RBD is to display the reliability of individual

items, while RBD groups are used to represent the reliability of a collection of items

configured in a particular manner e.g. multiple redundant items acting as a fail-safe

in the event of failure.

The connection between the two items represents an interdependency between them e.g.

for a fluid system consisting of a pipe and a valve, the valve can only fulfil its

function of controlling the flow rate of fluid if the pipe delivers the correct amount

of fluid to it. In another example, the connection from a reservoir of fluid to the

pipe, valve and outlet forms a complete path through the fluid system - this is known

as a reliability path. The connections and paths within an RBD group in MADE are used

to calculate the system reliability according to a RBD group decomposition technique.

RBD Analysis Workflow

The workflow below shows the steps taken to initiate a RBD analysis and generate an

output in the form of an updated model and RBD report.

[Image: rbdworkflow.png]

RBD Editor

[Image: rbdeditor0.png]

When first opened, the RBD editor shows items with no RBD grouping types assigned.

Each item is has its own reliability displayed underneath the block, based on its

duration of operation and reliability parameters entered by the user. The dashed lines

represent functional flow connections (referenced from the system model) between items.

[Image: rbdeditor.png]

The RBD editor above shows items assigned to series, redundancy and exclusion RBD

groups. Each group has its own shading, a display name at the top, a numbering schema

at the top right to denote its level of indenture and reliability value at the bottom.

To access the RBD editor:

1. Ensure the RAM module is active
2. Right-click an item in the Project Explorer or System Model
3. From the menu select "RBD Model" for the RBD editor or "ABD Model" for the ABD editor

[Image: rbdeditor.gif]

RBD Group Types

The RBD editor offers the following types of RBD groups:

• Series
• Parallel
• Complex
• Standby Redundancy
• K/N Redundancy
• Exclusion

Unless specified, MADE sets all items in a series RBD grouping. Select the RBD group

type in the list above to jump to its page which describes the group type in greater

detail.

The RBD analysis disregards functional feedback connections from the system model,

and so these connections are not displayed in the RBD diagrams. Feedback connections,

like regular functional connections are both represented as dashed lines in the RBD

editor and do not impact the RBD analysis in any way.

As the RBD model is auto-generated by MADE based on the existing functional and/or dynamic models, all rules relating to feedback are automatically assessed in the RBD analysis.