Presentations in FAM-C And FDM-A Methods and Some Problems of a Signals Theory

Abstract

The FDM-A diagnostic method [2, 4] based on a frequency modulation measurement of a pulsation component as well as the FAM-C method of an alternating current frequency have been elaborated in Air Force Institute of Technology. These methods to define a level of an assembly abrasive wear as well as its localization during a normal work of a power unit. A diagnostic signal is derived from onboard generators or alternators. Each damaged part of the generator’s or alternator’s power unit is a vibration generator or modulator. The vibration is turned into oscillation in onboard generators or alternators. After many years of the FAM-C and FDM-A methods’ using it is possible to localize and define value of many faults of power units: a coupling eccentricity, a shaft skew, extender longitudinal clearances of turbine engine’s rotor assembly, a frictional resistance of bearings, a smoothness of bearing’s rolling and a bearing cage, a break of rolling bearing’s separator, a misalignment of a rotor assembly’s support, etc. In FAM-C and FDM-A methods two kinds of presentations are used: first a presentation as characteristic patterns (analogous to Fourier spectrum lines but providing to observe periodical and stochastical phenomena) as well as the presentation of the frequency versus time. From the point of view of authors in many cases they are similar to presentations known from a theory of a radio signals transmission. It is possible to find carrier wale and side spectrum lines, beats caused by summation of two signals with approximate frequencies as well as many others. If analogy is so univocal, it is possible to use many systems and dependences used in telecommunication. For example: coherence demodulation (synchronous), which authors intend to use for separation characteristic patterns of two different mechanical assemblies with approximate vibration frequencies. At the end there are presented authors’ considerations, related to superposition of signals and beats as well as reflection of these phenomena in observed power units.