机器震动测试讲解.pptVIP

Why Make Condition Monitoring ? Types of Maintenance Time based preventive maintenance Protective Systems For avoiding sudden catastrophic breakdown Continuous measurements Simple measurements Relays for automatically tripping. What to Measure Different faults Where are vibrations coming from ? Force Mobility Vibration Measuring Mobility on simple structures Vibrations may be different from point to point Vibration standards are guidelines Create a reference for each measurement point Trending Making analysis gives earlier warning Frequency analysis Shorter time cycle, Higher Frequency Spectrum Analysis Acceleration Velocity Displacement Detector Fault Detection / Fault Diagnosis CPB vs. FFT CPB Spectrum Speed Compensation using CPB Classification of Machines Stationary signals No frequency analysis irrelevant Temperature Pressure Axial Displacement of shaft Radial displacement of shaft contains both: Stationary Dynamic Vibration (orbit spectrum) Harmonic signals Random Signals Random signals produce spectra without lines Most signals from machines is a combination of harmonic and random signals Following machine defect produce random signals: Cavitation Lubrication Problems Rolling Element Bearing faults Bearing Mounting defect Flow Exited Impulse signals Modulated Signals Torsional Load Gearboxes: Tooth Fatigue Eccentricity Frequency Modulation Amplitude modulation Produce sidebands Sideband spacing = carrier wave period Averaging Linear or Logarithmic Amplitude Fault Correction (Balancing) Summary Vibration gives the earliest warning of faults in rotating machinery Since the vibration value varies from point to point, each point should have individual reference. Frequency analysis of vibration gives a good assessment of machinery vibration. The CPB measurement gives the best fault detection Each machinery component has its own Potential Failure Mode which can be detected by vibration. Vibration signals can be a mixture of stationary, harmonic, modulate