8. Assessing Product Reliability
8.1. Introduction
8.1.7. What are some basic repair rate models used for repairable systems?

8.1.7.3.

Exponential law

The Exponential Law is another flexible NHPP model

An NHPP with ROCOF or intensity function given by 

is said to follow an Exponential Law. This is also called the log-linear model or the Cox-Lewis model. 

A system whose repair rate follows this flexible model is improving if  < 0 and deteriorating if >0. When  = 0, the Exponential Law reduces to the HPP constant repair rate model