Phase Analysis
Phase Analysis is a vibration diagnostic technique that measures the time relationship (phase angle) between a vibration signal at a specific machine location and a reference signal, typically from an optical tachometer or keyphasor. It determines the direction and timing of peak displacement of rotating components, distinguishing between forces like unbalance and stiffness issues like misalignment.
In shop floor maintenance, Phase Analysis is critical for diagnosing misalignment, unbalance, and mechanical looseness in rotating equipment such as motors and pumps. Technicians measure phase differences between coupling ends; a 180° phase difference indicates angular or parallel misalignment. Phase data enables precise placement of corrective weights for unbalance correction. In CMMS like ServiceGrid, phase angles are logged as condition-based monitoring evidence, triggering alerts if phase shifts significantly, indicating developing looseness or bearing wear. It also identifies resonance conditions by observing rapid phase shifts during speed changes.
How does Phase Analysis distinguish between rolling element bearing defects and unbalance?
Unbalance is a 1X synchronous force with a constant phase angle relative to the keyphasor. Bearing defects are non-synchronous; their phase is random or unstable relative to rotation, whereas unbalance phase remains stable.
What is the significance of a 180° phase shift in the axial direction?
A 180° axial phase shift between coupling halves is the definitive signature of angular misalignment, indicating the two shafts are at an angle to each other rather than parallel.
Why is dual-channel phase analysis required for critical fan diagnostics?
Single-channel phase measures only one point. Dual-channel analysis allows calculation of vibration vectors to distinguish between sway (rigid body motion) and bending (flexible mode), critical for preventing catastrophic fan collapse.