TABLE OF CONTENTS The bulk of reliability literature is devoted to activities for meeting a specified reliability requirement or evaluating the progress toward meeting it. Chapters 2 through 8 also fall into this category. However, at this point we will deviate from this pattern and address the question "How do you set a reliability requirement for a new or modified component or system?"
To introduce the principles used to answer this question, we consider equipment that is not subject to regulatory reliability oversight and where there is no interaction of failure modes. The concept of optimum reliability for such an item is developed in Section 9.1. The time relationship of the expenditures for cost of failure and failure prevention are discussed in Section 9.2, and practical guidance for estimating the cost elements is presented in Section 9.3. General rules for the cost of reliability improvement are developed in Section 9.4, followed by the chapter summary.
The concept of optimum reliability sounds strange, perhaps even perverse. Aren't developers motivated to make their product as reliable as possible? Of course, but they are constrained by the need to keep the product competitive in price and for getting it out on schedule. The costs and time required for failure prevention are concrete and must be faced immediately; the consequences of economizing in this area are much less concrete and occur in the future, if at all. In the following we look at concepts that can lead to a rational decision between the conflicting...
