Design of generalized delay timers for IID process variables based on alarm trigger and clearance rates

Alarm systems are commonly employed to alert industrial plant operators to take appropriate actions when process variables start to deviate from their normal operating ranges. However, contemporary alarm systems are suffering from excessive nuisance alarms.  Generalized delay timers are embedded functions of industrial alarm systems to remove nuisance alarms. This paper proposes a novel method to design optimal parameters of generalized delay timers. The degree of operator interference is determined by the frequency of false alarm activations and correct alarm clearances. Accordingly, the alarm trigger rate (ATR) and alarm clearance rate (ACR) characterize the performance of generalized delay timers under normal and abnormal conditions, respectively.Assuming that process variables under normal and abnormal conditions are both independent and identically distributed (IID), the proposed method determines the parameter set for generalized delay timers based on the user-desired ATR and ACR. The technical difficulty of the proposed method lies in deriving theoretical values of ATR and ACR based on the probability density functions of IID process variables and a certain parameter set. Numerical and industrial examples demonstrate the accuracy of the obtained results.