Basic Concepts We will introduce four important measures for the reliability of a nonrepairable item. The reliability(survivor)function R(t) The failure rate function z(t) The mean time to failure(MTTF) The mean residual life (MRL) We use variable X(t)to describe the state of an item X0= 1 if the item is functioning at time if the item is failed state at time The time to failure of item is denoted by T.Thus,T is a random variable. The time to failure T is not always the calender time.It may be other time concept:number of times a switch is operated,number of kilometers driven by a car,number of working cycles of a item.... CLGO System Engineering by J.J.Gao 10+ - System Engineering by J. J. Gao 10 Basic Concepts