Measurement instruments control with both accuracy and precision considerations

Abstract

Since any variation in the measurement process has a direct impact on the ability to make sound judgments about a manufacturing process, measurement is important in quality control and quality management. Measurement errors are caused by measurement instruments, and the MSA of both QS9000 and ISO/TS16949 has defined gauge capability acceptable criteria based on the Precision-to-Tolerance, P/T, value. However, measurement instruments with accuracy degeneration frequently occur in reliability engineering because components have nature failure rate. Thus, conclusions from gage capability studies by P/T values with no consideration of gage accuracy are not reliable. This study extends the index P/T to include both accuracy and precision considerations for the case A modified index P/T* is proposed to judge the gage capability. Moreover, we present the estimator of the index P/T* for the cases where a part can be measured once only and only one measurement instrument is used. Our method can both minimize the cost of frequent adjustment and properly monitor process quality. It is useful in any quality management or production planning strategy.

Keywords and phrases:

• Accuracy
• precision
• measurement errors
• gage capability analysis