Improvement of the failure diagnosis of flowmeters based on control limits - extension to the diagnosis method with two stages

摘要

The failure diagnosis of flowmeters based on control limits has been developed as a method that identifies faulty flowmeters, which should be calibrated during a maintenance period, under plant operation. This method is very useful for the diagnosis of flowmeters with faulty errors whose magnitude are over three times their control limits. However, there is a shortcoming such that the diagnostic results given by this method often become miss-alarm, or false diagnosis for the faulty errors whose magnitude are less two times their control limits. In this study, the diagnostic results given by this method under plant operation are not straightforwardly adopted. Instead, at least one flowmeter is selected and calibrated during a maintenance period to identify the true value of a flowrate. As a result, the diagnostic accuracy can be improved by performing the second diagnosis by use of the calibrated values of flowrates. Furthermore, the performance of the presented method is demonstrated by numerical experiments with the use of a simplified refinery model containing 11 flowmeters.