Research ArticleThe diagnostic line: A novel criterion for condition monitoring of rotating machinery

- Scaling properties of increment series are exploited for machine fault diagnosis.
- Data points for fault conditions can almost form a straight line.
- Data points for normal conditions considerably deviate from the straight line.
- A novel concept termed the diagnostic line is introduced to describe the phenomena.
- The novel criterion performs well in condition monitoring of rotating machinery.

This study examined scaling properties of an increment series from rotating machinery. Moreover, two fluctuation parameters for the smallest and largest time scales of a scaling range served as a pair of fluctuation parameters to describe system conditions. Therefore, an interesting phenomenon is observed: the data points, each representing a pair of fluctuation parameters, for fault conditions almost form a straight line, while those for normal clearly depart from the straight line. To describe the phenomenon, a novel concept termed the diagnostic line was introduced. Subsequently, properties of the diagnostic line were carefully investigated theoretically and numerically. Consequently, a decisive role of noise in forming the diagnostic line was determined. Accordingly, this study develops a novel criterion for condition monitoring of rotating machinery.