Experimental Modal Analysis (EMA)
MSI performs Experimental Modal Analysis (EMA) to determine the natural frequencies and characterize the vibration mode shapes of structures and mechanical systems. Knowing system natural frequencies and mode shapes is key to avoiding and/or diagnosing resonance. Resonance is the excitation of a system at one of its natural frequencies causing vibration amplitudes to increase unbounded until failure occurs, whether due to fracture in the short term, or fatigue in the long term.
EMA involves mechanically exciting the system under test via impulse, then measuring the resulting vibratory response. The impulse is most commonly achieved by striking the system with an instrumented hammer, while the vibratory response is measured with accelerometers. The size of the instrumented hammer is selected based on the system under test. Smaller systems require lighter hammers, which better excite the higher natural frequencies commonly associated with small or lightweight structures. Large systems, such as industrial turbomachinery, require heavier hammers capable of transferring the energy required to achieve a measurable response.
The resulting vibration ring-downs from several repeated impacts are measured for each response measurement location, with the responses from each strike averaged together to reduce noise in the data. Impacts are commonly applied in all three directions. The response accelerometers are typically placed at many locations around the system under test to create a comprehensive mapping of the vibratory motion. EMA can be performed on both stationary systems and on running systems to capture the effects of the forces and masses associated with operation on the natural frequencies. When performing EMA on operating equipment, MSI’s Time Averaged Pulse (TAP™) technique enables the extraction of natural frequency and mode shape information from the vibration signatures associated with normal operation.