FAULT DIAGNOSTIC SYSTEM

PURPOSE:To improve the working ratio of the facilities by providing an inferring/evaluating device which performs the inference/evaluation to check the presence or absence of a fault sign based on a knowledge rule related to the diagnoses of faults. CONSTITUTION:An estimating device 15 consists of an internal state estimating device 15a which estimates the internal state of the subject system 1 based on a knowledge rule set in consideration of the quantitative observation value Y(t) stored in a quantitative data base 13 and the design conditions of the system 1 as well as the processing result of a data processor 14 and an external observation value estimating device 15b. An inference/evaluation device 3b decides whether the system 1 may possibly have a fault or not based on the estimating result of the device 15, the latest value Y(t), and a knowledge rule related to the fault diagnosis. At the same time, the device 3b also decides a specific part of the system 1 that may possibly have a fault based on a knowledge rule related to the estimated external observation value. Thus the occurrence of a fault is estimated and the working ratio of the facilities is improved.