Indexing and Designing Deadbands for Industrial Alarm Signals

Abstract

Alarm systems play critically important roles for the safe and efficient operation of industrial plants, but they often suffer from too many nuisance alarms. Deadbands are widely used in industrial alarm systems to reduce the number of nuisance alarms. This paper formulates an index to determine whether deadbands are suitable for removing nuisance alarms of an analog signal, and proposes a method to design the deadband width. First, the deadband index is defined from two metrics, namely, normalized alarm durations and normalized alarm deviations. If the index is larger than 45°, as indicated by a hypothesis test, then nuisance alarms are associated with large/small normalized alarm durations/deviations, so that deadbands are suitable. Second, a design method is proposed to find an optimal deadband width, so as to achieve the best weighted balance between the time duration of nuisance alarms and the delay in detecting abnormal conditions. The proposed method is applicable to nonindependent and identically distributed (IID) signals, whereas available design methods are confined to IID signals. Industrial examples are provided to validate the deadband index and the design method.