Journal Article

An SPRT control chart with variable sampling intervals

Ou, Yanjing, Yu, Fong-Jung, Wu, Zhang, Shamsuzzaman, Mohammad

2011

Overview

The sequential probability ratio test (SPRT) chart is a very effective control chart. It is much faster to detect mean shifts compared with the and CUSUM charts, even their VSSI (variable sample sizes and sampling intervals) versions. This article proposes an SPRT scheme, called the VSI SPRT chart, which uses the variable sampling intervals (VSI) scheme to further increase the effectiveness of the SPRT chart for detecting process mean shifts. This VSI SPRT chart employs a long sampling interval d 1 when the process is likely to be in control and adopts a short sampling interval d 2 when the process seems close to an out-of-control condition. The results of the case studies show that the adaptive feature has the potential to further increase the overall detection effectiveness of the SPRT chart compared with the fixed sampling interval SPRT chart and, therefore, to reduce the manufacturing costs. This new chart is particularly effective when mean shift is moderate.

• Publisher: Springer-Verlag,Springer Nature B.V
• Subject: Adaptive control / CAE) and Design / Computer-Aided Engineering (CAD / Control charts / CUSUM charts / Economic models / Engineering / Industrial and Production Engineering / Intervals / Mechanical Engineering / Media Management / Original Article / Process planning / Production costs / Sampling