Synthesis of diagnostic features, appropriate to the piston machines technical condition types, main failures and operation modes, arising both separately and simultaneously, and invariant to the machine construction  is an important issue. One step for this problem solution is to create the diagnostic signal model for the unit under test.
The most common model of the known is a batch action generalized model of a quasiperiodic vibroacoustic signal, proposed by V.N. Kostyukov.
This model shows that the frequency content of the lowfrequency vibration spectrum and the vibroacoustic signal envelope, obtained by filtering in the highfrequency field and subsequent detection, are approximately equal. These spectra can be represented by an expansion in the characteristic frequencies, which can be divided into three groups. To evaluate the unit technical condition it is necessary to select and measure the components energy characteristics for each group.
This model describes large classes of the units under test failures. The model further development is the model, which describes the vibroacoustic signals with respect to their sources interaction, thus increasing the diagnosing accuracy and depth, but its use for developing the diagnostic algorithms is not obvious.
Therefore, it is advisable to consider a few examples of the vibroacoustic signal models when specific defects and failures occur, thus forming the piston compressors diagnostic features.
Naumenko A.P. Vibroacoustic model of the piston compressor diagnostic signal // Dynamics of systems, mechanisms and machines.  2009.  pp. 3944 Download the publication
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