Economic design of T2 control charts with the VSSI sampling scheme

T2 charts are used to monitor a process when more than one quality variable associated with process is being observed. Recent studies have shown that the T2 chart with variable sampling size and sampling interval (VSSI) detects a small shift in the process mean vector faster than the traditional T2 chart. The paper considers an economic design of the VSSI T2 chart, in which the expected hourly loss is constructed and regarded as an objective function for optimally determining the design parameters (i.e. the maximum/minimum sample size, the longest/shortest sampling interval, and the warning/action limits) in sampling-and-charting. Furthermore, the effects of process parameters and cost parameters upon the expected hourly loss and design parameters are examined.