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Component 1 Component 2 Component 3 Figure 3. RBD in a Parallel Configuration. While parallel configurations offer active redundancy, a system with a configuration depicted in Figure 4 offers a standby configuration. In the standby configuration, the component has redundant components which are not actively connected but are triggered by a switch. The original component is intended to last for the extent of its life; however, in the event that the component fails prematurely, a switch activates the redundant component to do the job. An example of the standby configuration would be two generators connected to a power grid having only one generator with an active load. If that generator were to fail, the other generator could be activated in its absence. Switch Component 1 Component 2 Component 3 Figure 4. RBD in Standby Configuration. A load-sharing system is one where the components are arranged in a parallel configuration, but each component equally shares a system's function. An example of this is a set of two identical fuel pumps each producing x/2 gallons per hour. If the requirement were that x gallons per hour were required, then both pumps would be required not to fail in order to keep the system operational. In this case, the extra components act to share the overall load of the system rather than acting as an active redundancy. The final general form of RBD is the complex form. In reality, most systems will not be strictly parallel or series but are often some combination of the two. Figure 1 of the previous page shows a system that is a parallel-series hybrid. These systems can be analyzed by breaking the system into each of the parallel and series modules to determine the effect of failure. 3.2 Reliability Allocation. After the system has been drawn in block diagram form, subsystem and component reliability goals and targets are established. This is a common 5

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