A study on exponentially weighted moving average control chart for monitoring dissolved oxygen in Nan river

การศึกษาแผนภูมิควบคุมค่าเฉลี่ยเคลื่อนที่ถ่วงน้ำหนักแบบเลขชี้กำลังเพื่อตรวจสอบปริมาณออกซิเจนละลายในแม่น้ำน่าน

Abstract

The objective of this study was to construct the exponentially weighted moving average (EWMA) control chart for monitoring dissolved oxygen in the Nan river by using residual from the autoregressive integrated moving average (ARIMA). The daily data total 243 values, the result shows that model is ARIMA(1,1,4) non-constant value and the accuracy was considered by root mean square error is 1.003. When the control limit parameter was set to a constant 3 and the statistical parameter of the EWMA control chart with a difference values. As the results, we found that the EWMA control chart with varies constant of EWMA statistic ( ) and the constant of control limit is 3, =0.05, the residual is out of the lower limit 7 values when  are 0.1 and 0.25, the residual is out of the lower limit 11 values. For  are 0.15 0.2 and 0.3 respectively, the residual is out of the lower limit 12 values. In addition, showed that on some days the water would be used water only for transport water.