Training courses, technical publications and other resources such as online resources and commercial self teaching material are available that can improve analysis skills and shorten the learning curve. Phase and magnitude were measured from permanently mounted X and Y displacement probes on a turbine generator. Relative phase is the most convenient way to measure phase on a machine because the machine does not need to be stopped to install reflective tape on the shaft. Good alignment will show no substantial phase shift between bearings or across the coupling. Figure 10. Phase can be measured at any frequency. As expected, the fan vibrates due to an unbalanced fan wheel. Soft foot on a motor distorts the stator housing creating a non-uniform rotor to stator air gap resulting in vibration at two times line frequency. A bump test was also recommended to further locate and analyze the resonance vibration. Mechanical Looseness Looseness is characterized by harmonics of TS with raised noise floor. Aims and Scope; Editorial Board; Titles in Series. Instead of comparing the phase and magnitude numbers from a table or bubble diagram, operational deflection shape software (ODS) can be used to animate a machine drawing. Relative phase is measured on a multi-channel vibration analyzer using two or more (similar type) vibration sensors. Mechanical defect identification for gas‐insulated switchgear equipment based on time‐frequency vibration signal analysis Yao Zhong, Jian Hao, Ruijin Liao, Xupeng Wang and Xiping Jiang et al. The initial assessment of the fan unit showed the unit to run normally when one fan was running, but once the second fan was turned on, vibration issues presented themselves at certain set points. The data no longer matches the fault patterns we have learned. The machine in Figure 12 has a 180-degree phase shift across the coupling in the radial directions. The axial directions are in-phase across the machine. Velocity measurements and monitoring of vibration is the most common unit to identify various problems or acceptability such as: unbalance, misalignment, looseness (machinery structural, foundations, or bearings), harmonics, and many other issues in the machinery frequency range and many multiples of actual speed. hbspt.cta.load(3951034, 'e84dcc94-6e63-48f1-b2ac-0381ec9f447a', {}); How to Use Vibration Analysis to Identify Equipment Problems, Acoustic Emission: The Next Generation of Vibration Techniques, The Cost Effective Benefits of a High Performance Kidney Loop System, 8 Steps to Successfully Implement a Preventive Maintenance Program, Empty space or bubbles (cavitation) in pumps. Vibration Spectrum Analyzers use the signal from different types of sensor, such as: accelerometers, velocity transducers and proximity sensors. Phase is used to detect cocked bearings and bent shafts. All of this data is analyzed by computer program algorithms, which in turn is analyzed by engineers or trained vibration analysts to determine the health of the machine and identify possible impending problems like looseness, unbalance, misalignment, lubrication issues and more. Vibration analysis revealed that once fan No. If the phase difference is closer to zero or 180 degrees, the vibration is caused by a reaction force. Trend plots show changes in a measurement over time. A phase shift between the foot and mount may indicate soft foot. No vibration analyst wants to make the wrong call. All data collected from the accelerometer goes directly into a data collector (software), which records the signal as either amplitude vs. time (known as time waveform), amplitude vs. frequency (known as fast Fourier transform), or both. Phase is used to detect loose joints on structures and bending or twisting due to weakness or resonance. At a minimum, all machines have some unbalance and misalignment. Good ODS software can make it easier to analyze phase and magnitude data from a large number of test points. A phase study might include hundreds of test points measured all over the machine and foundation. Mathematical Methods and Modeling. • Identifying the problems along with their severity to schedule corrective action including mass unbalance, misalignment, soft foot, bearing fault analysis, gearbox faults, mechanical looseness, and electrical problems. Record the values in a table or bubble diagram as shown in Figure 12. Figure 9. While the inner-workings and formulas used to calculate various forms of vibration can get complicated, it all starts with using an accelerometer to measure vibration. Phase is the position of a rotating part at any instant with respect to a fixed point. Figure 8 is an example of the phase shift across a soft foot. Tuning a car engine using a timing light and inductive sensor is an application of phase analysis (Figure 2). We would like to show you a description here but the site won’t allow us. If the phase angle is different by more than 20 degrees, the foot is loose or the machine frame is cracked or flimsy. An ODS is an extension of phase analysis where a computer-generated model of the machine is animated with phase and magnitude data or simultaneously measured time waveforms. If a machinery problem exists, FFT spectra provide information to help determine the source and cause of the problem and, with trending, how long until the pr oblem Cocked Bearings and Bent Shafts
It can be caused by a condition where the foot of a motor, pump or other component is not flat, square and tight to its mounting, or many other things, such as machining errors, bent or twisted feet and non-flat mounting surfaces. Phase can be used to identify soft foot while the machine is in operation. Vibration measurements are taken on each bearing location in three planes: vertical, horizontal and axial. If the shaft is straight and the bearing is not twisting, the phase will be the same at each location (Figure 9). Some software can continuously monitor the geometry of your rolling elements and warn you when possible premature failures may occur. Vibration analysis can detect problems such as: Distributor and alignment and maintenance training provider VibrAlign uses the example of taking an industrial fan, removing a fan blade and starting it up. Relative phase is the time difference between the waveforms at a specific frequency converted to degrees (Figure 6). Measure each bearing in the horizontal, vertical and axial directions. Absolute phase is required for rotor balancing. Multi-channel vibration analyzers like the Pruftechnik VibXpert illustrated in Figure 7 have standard functions for measuring both absolute and relative phase. A phase study is a collection of phase measurements made on a machine or structure and evaluated to reveal information about relative motion between components. Vibration sensors, instruments and software are able to provide key information about machine health. He can be reached at 585-293-3234 or www.4xdiagnostics.com. Measure vertical phase between the foot and its mounting surface.