Two-Sided Charts for Monitoring Nonconforming Parts per Million

Processes with a low fraction of nonconforming units are known as high-yield processes. These processes produce a small number of nonconforming parts per million. Traditional methods for monitoring the fraction of nonconforming units such as the binomial and geometric control charts with probability limits are not effective. In order to properly monitor these processes, we propose new two-sided geometric-based control charts. In this article we show how to design, analyze, and evaluate their performance. We conclude that these new charts outperform other geometric charts suggested in the literature.