Based on co-spectrum characteristics

Subject to availability of a RPM sensor and vibration pickups, it is possible to define an imbalance of shaft, its type and location (kind of shaft oscillations, bearing, on which large vibrations occur, and angle of rotation relative to a mark point of pressure sensor). The figure shows the co-spectrum phase of two signals — of the RPM sensor and vibration pickup. In the vicinity of shaft frequency of 90 Hz the angle of divergence of two signals is approximately 130 degrees. This data can be used for the shaft balancing.

The degree of coherence — a ratio of co-spectrum modulus to the values of power spectrum of each measurement channel — defines the relationship between two processes. In this case, the degree of coherence between the signals of RPM sensor and vibration pickup at the shaft frequency is close to 100%, indicating that the vibrations measured by the vibration pickup at the frequency of approximately 90 Hz are determined by the shaft rotation.

See also:

• diagnostics of gear units;
• diagnostics of gear units based on spectrum of vibration signal;
• diagnostics of gear units based on super narrow-band spectrum;
• diagnostics of gear units based on inter-correlation characteristics;
• diagnostics of gear units based on spectrum of envelope curve;
• diagnostics of gear units based on order normalization.