Further Comments on "The Reliability of Periodically Repaired n –l/n Parallel Redundant Systems"

In the original correspondence,1 Cantarella assumed a system consisting ot n parallel identical elements, each with a constant failure rate A. The system is repaired every T hours. An approximation n(n -1) A2T/2 for the average failure rate was derived. In further correspondence, 2 Nilsson derived an exact ciosed form expression for the failure rate. In this comment, we correct an algebraic error in Nilsson´s approximation for small values of A. T, and also point out the relevance of both correspondences to the case where n is small, as in a triple modular redundant (TMR) system.