Series, Parallel and Series Parallel Combination Configurations

The simplest and most elementary configurations of an RBD are the series and parallel configurations. Items placed in series must all work for the system to work, as shown in Figure 1, where the system fails if either A, B or C fails.

Items placed in parallel are considered to be redundant, as shown in Figure 2, where either D or B can fail and the system will continue to function. The concept can be expanded further, as shown in Figure 3, with combinations of series and parallel configurations in the same diagram. These elementary configurations form the basis of the reliability block diagram constructs.

Figure 1: Series Configuration

 

Figure 2: Parallel Configuration

 

Figure 3: Combination of Series and Parallel Configurations