k-out-of-n Nodes

The k-out-of-n node allows the analyst to specify an alternative form of redundancy known as k-out-of-n redundancy. A k-out-of-n node can have n paths leading into it, and requires that k of those n paths must function for the system to function.

Figures 1 and 2 present reliability block diagrams (RBD) that incorporate such nodes. The configuration in Figure 1 includes a k-out-of-n node where either B, C or D must operate for the system to function but any two of the other items may fail without causing system failure. With the traditional reliability block diagram methodology, k-out-of-n redundancy could have been specified for units drawn in parallel. However, with the introduction of the node element in the diagram, one can specify such redundancy for complex configurations, such as the one shown in Figure 2.

Figure 1: k-out-of-n Node Configuration

 

Figure 2: Complex Configuration with 2-out-of-5 Node