The Standard Deviation Of Asymmetric Control Map And Its Criterion

Statistical Process Control is an important aspect in Statistical Quality Management. We tried to make some analysis on this aspect in this article.This article consists of two chapters. We give the summaries as follows:Chapter 1: The standard deviation chart of National Standard is symmetrical and based on "3σ" principle of normal distribution. We proposed the idea of asymmetrical standard deviation chart based on the statistical characteristics of standard deviation in this article, constructed three types of asymmetrical standard deviation charts and worked out their coefficients of upper and lower control limits at the alert rate of 0.27%. In practice, engineers can use these results very easily. These three types of asymmetrical standard deviation charts have their own characters, which were introduced in this article. We also compared them with the standard deviation chart of National Standard in the respects of Average Run Length (ARL), ratio of the ARL and trend of ARL.Chapter 2: We proposed the eight criteria determining the singularity of asymmetrical standard deviation chart based on the eight criteria determining the singularity of chart in this article and worked out their alert rates. We also compared them with the standard deviation chart of National Standard in the respects of ARL. Unbiased control chart is the most attractive because of the good characteristic of unbiased.