ELEKTROnet 2006/1: Machine Fault Diagnostic and "Expert" Systems

Rahne Eric, B.Sc. in Electrical Engineering, founder of PIM Professional Industrial Measurement Technology Ltd., vibration diagnostic expert

Along with information technology, devices and technologies for assessing the condition of rotating machinery have undergone tremendous development in recent years. Initially, vibration level measuring devices, and then portable broadband vibration data collectors, emerged. Their popularity was primarily due to their simple usability (e.g., not requiring expertise, "very easy" operation) and relatively low prices. A little later, vibration analyzers (spectrum analyzers) and data collecting spectrum analyzer instruments began to spread. The diagnostic information that can be "read" from the data obtained with these devices (spectrums) is suitable for recognizing even more machine faults, but this technology requires a knowledgeable and experienced professional. A further milestone was the addition of information to the peaks list of vibrations, indicating which numerically determinable fault frequency (e.g., rotational frequency, bearing fault frequency, blade frequency, gear frequency) or its multiple, or sideband combination, corresponds to the currently displayed vibration peak frequency. Those who have trouble "reading" spectra can immediately compile a text-data set, based on which they can infer the present machine faults. However, the biggest problem with this method is that the typical frequencies of many machine faults are the same, making their separation rarely feasible or very uncertain. To address this issue, PC software has appeared on the market (e.g., from the American company CSi for almost two decades), which performs vibration diagnostic signal processing and is capable of textually indicating the most probable machine faults using logical rules and statistical relationships. These evaluation systems are commonly referred to as "automatic diagnostic" or "expert" systems. In their case, machine diagnostic knowledge (or more precisely: the logic of the diagnostic procedure, decision-making mechanisms) is practically built into the software. According to instrument manufacturers, the "knowledge" embedded in such systems is often deeper, more comprehensive, more diverse, and more logically structured than what anyone could acquire over many years. Expert systems can be very well integrated into the operation-maintenance system, but they must be used in places and under conditions where they are cost-effective and efficient. We should not expect miracles from them, and we must accept that only faults in those machine components, parts can be detected that have been defined with due care, or only faults can be identified with high probability for which the necessary measurement data have been collected. Even for a vibration diagnostic expert, a well-defined expert system can provide significant assistance (especially in the case of a large number of measurements), as it does not tire, is quick, and free from subjectivity. Overall, when selecting an expert system, it is essential to keep in mind that the selection, installation (database setup) of the system requires very serious machine and machine diagnostic knowledge, the responsibility is huge, so it matters who is entrusted with all this. A poorly defined system, no matter how many tens of millions of HUF it cost, will never efficiently perform the tasks assigned to it in operation-maintenance. And above all, do not treat the system as a miracle cure that can be used instead of professionals - this will definitely end in failure. PIM Professional Industrial Measurement Technology Ltd. H-1221 Budapest, Tanító u. 19/A Tel.: (1) 424-00-99 Fax: (1) 424-00-97 e-mail: pim@pim-kft.hu web: www.pim-kft.hu www.termokamera.hu www.gepszakerto.hu

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