Double sampling np chart with estimated process parameter

This study presents a double sampling (DS) np chart when the process parameter is estimated. The DS np chart is evaluated in terms of the average of the average run length and the standard deviation of the average run length. The results show that a large number of Phase-I samples is required for designing the DS np chart. Since it is unrealistic in practice to obtain a large amount of Phase-I data, a combination of new design parameters for the DS np chart with estimated process parameter is computed by taking the number of Phase-I samples into consideration.