Design for an SPRT control scheme based on linguistic data

Products are generally classified in a binary manner (conforming or non-conforming) in attributed control charts. This format may not be the most suitable if the product quality changes gradually rather than abruptly. Therefore, re. ning the partition into multiple categories will lead to a reduction of quality information loss. To enhance the detection ability of a control chart, linguistic variables are used here to express the quality characteristics and a sequential probability ratio test scheme is constructed under the estimated probability distribution function of the linguistic data. The simulation results show that the sequential probability ratio test charting procedure has a better performance than the Shewhart control chart for the small magnitude of process mean shifts in terms of average run lengths.