![]() There are advanced methods, including Artificial Intelligence techniques, which address all three of these. The third is the detection of an incipient malfunction which has not yet resulted in a fault or an alarm. The second is the handling of alarms caused by some fault or operator action, the diagnosis of the fault and the response to it. One is the detection of a disturbance or abnormality which falls short of an identifiable fault and which does not necessarily result in any process alarm. Sam Mannan, in Lees' Process Safety Essentials, 2014 20.16 Process Monitoring ![]() ![]() It thereby exploits redundant analytical relationships among various measured variables of the monitored process and avoids replicating every hardware separately. Analytical redundancy is a more accessible strategy that compares the measured variable with the predicted values from a mathematical model of the monitored system. Unlike a physical redundancy, which is performed by adding more sensors (hardware) to measure a specific process variable, the analytical redundancy does not require additional hardware because it is based on using the existing relations between the dependent measured variables that are or are not of the same nature. This approach is mainly only justified for critical systems, such as nuclear reactors and aeronautic systems. In addition, this method is limited in practice to sensor faults and cannot detect faults in variables that are not measured directly. In practice, the main disadvantage of hardware redundancy is the additional cost of equipment and maintenance, as well as the space needed to install the equipment that increases complexity considerably in the already very complex systems. This strategy has been widely used in the industry because of its reliability and simplicity of implementation. Typically, fault detection and isolation are achieved by a majority vote between all the redundant sensors. Specifically, under normal conditions, one sensor is sufficient to monitor a particular variable, but adding at least two extra sensors is generally needed to guarantee reliable measurements and monitoring under faulty conditions. To detect and isolate simple faults, the number of sensors to use should be doubled. The essence of hardware or physical redundancy, which is a traditional method in process monitoring, consists of measuring a particular process variable using several sensors (e.g., two or more sensors). ![]() There are two types of redundancy in the process: physical redundancy and analytical redundancy ( Fig. Process monitoring is essentially based on the exploitation of redundant sources of information. ![]()
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