Process capability indices and X , R control chart limit adjustments by taking into account measurement system errors

This paper investigates the effects of measurement system variability arising from evaluations of process capabilities. In this work, relationships between true process capability indices, Cp,True and Cpm,True, and their corresponding observed indices, Cp,Obs and Cpm,Obs, are developed depending on the levels of type I and II errors. Moreover, the method for adjusting control chart limits used to monitor the process is proposed based on measurement system variability. An industrial case study is used to highlight the findings of this investigation and to discuss the adjustment levels that should be conducted depending on the values of type I and type II errors