Design of Sensors for Process Fault Diagnosis
Alarm systems differ from normal monitoring systems. Although the basic goal of monitoring systems is to provide a good estimate of the state of the system, alarm systems are designed to detect process malfunction. In turn, process faults, which typically have only one source in some unit, propagate throughout the process, altering the readings of instruments (pressures, temperatures, flow rates etc.). Thus, these sensors should be able to determine departures from normal operation. In this sense, this task is different from that of gross error detection, which concentrates on instrument malfunction instead. As a consequence, the discrimination between instrument malfunction is an additional task of the alarm system. Thus, the problem of designing an alarm system consists of determining the cost-optimal position of sensors, such that all process faults, single or multiple and simultaneous, can be detected and distinguished from instrument malfunction (biases).