TABLE OF CONTENTS Reliability prediction (i.e. modelling) is the process of calculating the anticipated system RAMS from assumed component failure rates. It provides a quantitative measure of how close a proposed design comes to meeting the design objectives and allows comparisons to be made between different design proposals. It has already been emphasized that reliability prediction is an imprecise calculation, but it is nevertheless a valuable exercise for the following reasons:
It provides an early indication of a system's potential to meet the design reliability requirements.
It enables an assessment of life-cycle costs to be carried out.
It enables one to establish which components, or areas, in a design contribute to the major portion of the unreliability.
It enables trade-offs to be made as, for example, between reliability, maintainability and proof-test intervals in achieving a given availability.
Its use is increasingly called for in invitations to tender, contracts and in safety-integrity standards.
It must be stressed that prediction is a design tool and not a precise measure of reliability. The main value of a prediction is in showing the relative reliabilities of modules so that allocations can be made. Whatever the accuracy of the exercise, if one module is shown to have double the MTBF of another then, when calculating values for modules in order to achieve the desired system MTBF, the values allocated to...
