JFET_V4_N2_A2 Ramasamy Sivasamy P.M. Kgosi Journal on Future Engineering and Technology 2230 – 7184 4 2 17 21 Extended Available Period, Inspection Period, Unit Failure, System Breakdown, Markov Renewal Process, Reliability, Availability, Rate of Change in Cost Per Unit time A Single unit Programmable Logic Controller (PLC) operating simultaneously till either the random inspection period or the random extended available period is over whichever occurs first after the failure of the online unit is considered in this paper. Postulating the operative phase, partial system failure phase, repair phase, and replacement phase of that online unit as states of a Markov Renewal process (MRP) in a time cycle reliability indices and availability characteristics were obtained and it has been shown that profit will be constant in the context of increase in cost per unit time of inspection, repair and replacement and numerically illustrated and presented in a table. November 2008 - January 2009 Copyright © 2009 i-manager publications. All rights reserved. i-manager Publications http://www.imanagerpublications.com/Article.aspx?ArticleId=507