Alarm Monitoring for Multivariate Processes Based on a Convex-Hull Normal Operating Zone

Abstract

Alarm monitoring, which is implemented by an alarm system, is to generate alarms for a process through certain mechanisms when the process is in the abnormal condition. This brief proposes a method to design an alarm system with dynamic alarm limits for multivariate processes. A normal operating zone (NOZ) described by a convex hull is established from the historical normal data points based on a formulated fitness index, and dynamic alarm limits of each process variable are developed based on the established NOZ. If all process variables are inside their own dynamic alarm limits, the process is in the normal condition and no alarms are raised; otherwise, the process is in the abnormal condition and alarms will occur. The designed alarm system can avoid false alarms from the conventional one using static alarm limits, owing to a fact that dynamic alarm limits of one process variable are related to other process variables. In addition, unlike designing alarm limits for latent variables with no specific meanings, each process variable has its own dynamic alarm limits that have the same physical meaning as the process variable. Industrial examples are provided to illustrate the effectiveness of the proposed method.