Modeling Multiple Preventative Maintenance Actions in a RAMS Analysis

This paper describes how multiple preventative maintenance (PM) activities can be modeled in the availability and reliability analyses of complex systems, using popular off the shelf software. This is a necessary and critical step for an understanding of the downtime implications of certain electromechanical subsystems and systems, but is not always easy to model with all software packages.

Quite often, maintenance and service related actions are an afterthought in reliability and availability calculations. This is because most electronic systems require minimal maintenance of electronic circuit boards, components and sub systems. Dust filter replacement, inspection (and perhaps calibration) are the primary activities usually needed. As a result, many find it prudent to ignore these activities because they are second or third order effects. In most cases, they do not even require downing the system.

However, electromechanical devices and assemblies are different. There are many situations where several maintenance activities on an ongoing, repeatable schedule are required in order to prevent premature faults and extend the useful life of the device. This is especially true of engines, motors, generators, cooling fans and any device that includes bearings or mechanical movement. In addition, downing of the system is usually necessary to perform the needed maintenance.

This paper discusses an actual example of a radar power plant reliability block diagram with redundant gensets that shows how the maintenance dominates the down time and how failure rates play a lesser role in the availability of the power plant.