TABLE OF CONTENTS Fault Trees and Reliability Block Diagrams are both methods of showing probability combinations. There have been a number of solution techniques developed to solve probability combinations. These include Cut Sets, Tie sets, Event Space, Decomposition Method, Gate Solution Method, and many others. In this appendix three examples will be shown - the Event Space method and the Cut Set method, and the Gate Solution Method. Details and full development of the methods can be found in (Ref. [1]) Chapter 5.
This chapter will also discuss and explain the potential problems of PFavg calculation with any probability combination method like fault trees. Probability averages must be taken after logic is applied, or else significant errors may result.
[1]Billinton, Roy and Allan, R.N., Reliability Evaluation of Engineering Systems: Concepts and Techniques, NY: New York, Plenum Press, 1983.
One technique that provides a comprehensive overview of a probability combination model is the event space method. The authors have used this technique especially when a detailed knowledge of probability combinations is needed to optimize a design. The method is called systematic and comprehensive.
Consider the example of a 2oo3 redundant power supply system as shown in Figure C-1. The system consists of three diverse power supplies each capable of providing 100 watts of power. The total load on the system is 175 watts. Therefore, the system can be successful in delivering 175 watts if only two of the three power subsystems are available. The fault tree...
