Availability of a periodically inspected system under perfect repair

We study the availability of a system that is maintained under periodic inspection and a perfect repair policy with constant repair time. We consider two models. One, Model A that treats an unfailed system to be as good as new upon inspection, and makes perfect repair of a failed system with immediate restoration. Two, Model B that does not intervene on a system found unfailed at inspection times and makes perfect repair of a failed system with restoration taking place at the next scheduled inspection following repair. For each model, we express the system availability function as a linear combination of the survival function and its shift(s), and, thereby, obtain the limiting average availability. We illustrate the results when the system has exponential or gamma life distribution. Graphs of the system availability function, and numerical tables showing the limiting average availability and the periodicity of inspections necessary to achieve a specified limiting average availability are also presented. (C) 2000 Elsevier Science B.V. All rights reserved. MSC: primary 90B25; secondary 62N05.