4
Reliability
I. INTRODUCTION
The reliability of a component or system can be represented in a statistical
sense by the probability of a component or system performing satisfactorily
at a particular time under a specified set of operating conditions. The definition of what constitutes ’satisfactory’
may depend upon the nature of
the system. Some devices, such as switches and valves, may have only
an ’operate’ or ’non-operate’ mode. Other devices may be judged satisfactory or not depending on the required output level of some performance
variable such as power or thrust. The present introductory discussion will
consider the first two of the following four aspects of reliability:
1. The change in reliability
of a component or system with age
2. The reliability of a system as influenced by the arrangement of
components
3. The precision of estimates of reliability
and other associated
reliability parameters
4. The ability of a product to perform within specified limits under
the influence of some external stress or environment
The object of the present discussion is to introduce some basic concepts and
complete treatments can be found in the various references cited.
This major emphasis to date on the use of mathematical reliability
models has been in the aero-space and defense industries. Particular attention has been given in the literature to studies of electronic systems. There
has been somewhat less emphasis on the mathematical aspects of reliability
as applied to mechanical systems. The reduced emphasis is not due to lack
of interest, but rather to the comparatively high reliability of typical mechanical systems. In addition, high unit costs (of equipment for testing
specimens) and the lengthy test requirements (because of good existing
reliability) have limited the number of studies. Although complex electronic
187
Reliability
I. INTRODUCTION
The reliability of a component or system can be represented in a statistical
sense by the probability of a component or system performing satisfactorily
at a particular time under a specified set of operating conditions. The definition of what constitutes ’satisfactory’
may depend upon the nature of
the system. Some devices, such as switches and valves, may have only
an ’operate’ or ’non-operate’ mode. Other devices may be judged satisfactory or not depending on the required output level of some performance
variable such as power or thrust. The present introductory discussion will
consider the first two of the following four aspects of reliability:
1. The change in reliability
of a component or system with age
2. The reliability of a system as influenced by the arrangement of
components
3. The precision of estimates of reliability
and other associated
reliability parameters
4. The ability of a product to perform within specified limits under
the influence of some external stress or environment
The object of the present discussion is to introduce some basic concepts and
complete treatments can be found in the various references cited.
This major emphasis to date on the use of mathematical reliability
models has been in the aero-space and defense industries. Particular attention has been given in the literature to studies of electronic systems. There
has been somewhat less emphasis on the mathematical aspects of reliability
as applied to mechanical systems. The reduced emphasis is not due to lack
of interest, but rather to the comparatively high reliability of typical mechanical systems. In addition, high unit costs (of equipment for testing
specimens) and the lengthy test requirements (because of good existing
reliability) have limited the number of studies. Although complex electronic
187