Cross Channel Phase Explained
Phase analysis is an effective means of diagnosing machine faults such as misalignment, resonance, soft foot and looseness among others. Phase analysis is also useful in distinguishing faults that look like imbalance but are actually caused by something else (such as misalignment, which can show up at 1X RPM similar to imbalance). Knowledge of the phase relationships of various machine faults will help to confirm the existence of a specific machine fault and help to prevent misdiagnosis.
Cross channel phase is a convenient method of taking phase measurements that does not require the use of a tachometer or reflective tape. Instead, phase is measured between two sensors.
Note: When taking measurements, be aware of the direction each sensor is facing. If you are measuring across the coupling in the axial direction you will probably turn the sensors in opposite directions, thereby introducing an additional 180° phase change. Remember to take this into consideration when analyzing the phase measurements.
Recommendations for cross channel phase
- Determine the exact frequency of interest by using spectra to identify high amplitude peaks at specific frequencies.
- Position the channel 1 sensor in a location which has high vibration at this frequency. Do not move this sensor once testing has started.
- Try out different locations with the channel 2 sensor, noting the phase and amplitude relationships compared to the fixed channel 1 position.
- Repeat steps 2 and 3 at any other locations of interest.
Last Reviewed: 11/Jun/2009 Source: vbSeries Reference Guide Revision 24 Mar 2009 - pages 74 & 75