Characterizing the Output Process of a CONWIP Line with Deterministic Processing and Random Outages

We model a CONWIP (CONstant Work-in-Process) production line with deterministic processing times and exponential failure and repair times as a closed queueing network. We derive an approximation for the mean and variance of the output during a specified interval and give computable conditions under which this approximation performs well. We show through empirical tests that the approximation is robust and illustrate its usefulness as the basis for a procedure for selecting an economic production quota and a card count for a CONWIP line.