Abstract: An deviation E between a setting value SV and an actual phase value PV in a controller is integrated, and the resulting integrated value S is compared with a predetermined threshold D for detecting a malfunction. Checking a change in setting value SV, checking an increase or a decrease in deviation E and comparison with the absolute value .vertline.E.times.S.vertline. are made to ensure stability against fluctuations and rapid detection of a malfunction.

Abstract: The present invention relates to a plant fault diagnosing system for diagnosing the operating conditions of the plant, for example, change in the physical quantity or whether any fault is present in each of the instrumentations or not. This system makes reference and makes directly comparison the process data of the plant or a diagnosing pattern processed by treating the process data in a predetermined process with a predetermined information for detecting showing the symptom of an abnormality or a predetermined reference value. When any deviation from a predetermined allowable range or coincidence of the patterns is detected, it determines that there is any abnormality in the plant, and issues an alarm to, for example, an operator.

Abstract: A method and apparatus detect a noise disappearance of instruments, etc. in various instrumentations in a chemical plant or the like. Detection values which are outputs from a detector (1) are input into a data store (3) via a data collector (2). Inputs to a processor (4) are a detection value (Sold) at a previous point and time from the data storer (3) and further a current detection value serving as a newest value (Snew) from the data collector (2). In the processor (4), an absolute difference between the newest value (Snew) and the previous value (Sold) is calculated. When this difference is smaller than a preset value, a count number (C) of a counter (5) is incremented, whereas when this difference is larger than the preset value, the count number (C) is cleared. When the count number from the counter (5) exceeds a predetermined threshold value, this is regarded the occurrence of a noise disappearance, and a trigger signal (T) for actuating a notifier (7) is output from a limiter (6).