Gráficos de controle de Shewhart, CUSUM e EWMA: um estudo comparativo em verificação intermediária de balanças

Abstract

The quality assurance of measurements results generated by testing and calibration laboratories based on ABNT NBR ISO/IEC 17025 is directly associated with process monitoring undertaken by their measuring instruments. This process monitoring may be carried out through the application of control charts (CC) and, for this study, four electronic weighing balances pertaining to two laboratories at a Federal Institution of High Education were chosen as measuring instruments to be analyzed. The main objective of this research is to identify the most appropriated CC for monitoring trends on these electronic scales, between CUSUM, EWMA and Shewhart CC. It became necessary to define the period of data analyzes collected by these laboratories, to calculate the control limits for each CC (phase I), to carry out the process monitoring (phase II), following by the comparison between these three CC. Minitab Statistical Software 17 was used for the CC construction. This study identified the EWMA CC as the best alternative to be used for monitoring trends in all points of the intermediate checks because it is the only CC that can be applied for both normal and non-normal data. It was not possible to identify which of the CC detects the special-causes earlier.