Sound Power on CoCo-80X

The CoCo-80X’s latest software release includes a new signal analysis project for Sound Power applications. The Sound Power CSA features a graphic interface to show the test point status. There are multiple test room types and microphone arrangements. When the test is complete, a report is generated.

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Crystal Instruments exhibited a highly advanced new set of tools called “EDM Modal”, at IMAC 2019 in Orlando, Florida. IMAC XXXVII maintained a broader focus and chose this year’s theme as “Predictive Modeling for Engineering Design and Decision Making.” The conference took on a note of focusing more on general-purpose data acquisition while still maintaining a strong academic focus on the principles of modal analysis.

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Modal Testing Using the CoCo-90X

Studying the modal properties of the structure under test is important to optimize the design of the test structure and to improve the NVH characteristics. Finite Element Analysis is widely used to obtain the mechanical properties of different objects. However, it is not only difficult to replicate the exact environmental constraints and boundary conditions but also challenging to obtain the damping ratios of the different modes. Experimental modal analysis not only helps in solving these issues but can also help in validating the results of the finite element model.

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Hammer Impact Test Considerations

Roving excitation or response? Uni-ax or Tri-ax? SIMO or MIMO?

A modal impact hammer test is broadly classified between two types: roving hammer and roving response. Each method has its own pros and cons.

Implementing the aforementioned methods to perform measurements in one direction (usually out-of-plane) using a single uni-axial accelerometer yields a row of FRF when roving hammer, or a column of FRF when roving sensor. In the case of a FRF column, it is necessary to switch the response and excitation of the DOF of each FRF signal to yield a row of FRF. Curve fitting the row of measured FRFs produces the modal parameters of the test structure.

However, some tests may use more than one accelerometer or measure data in more than one direction. Even though the basics are still the same, care must be taken while performing the experiment to ensure that there is either a complete row or a complete column of the frequency response function. If the resulting FRF signals does not contain this, then the natural frequencies, mode shapes and damping of the structure cannot be obtained.

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Spider-80SG Interface with Rod End Load Cell

Measurements can be broadly classified into two categories: Static Measurements and Dynamic Measurements.

Dynamic measurements vary greatly over a short period of time (e.g., Vibration (Acceleration), Audio (Sound pressure), etc.). In these types of signals, we are mainly interested in the high frequency components so measurements down to DC are typically not necessary. For these measurements, we would use the AC input mode (or IEPE) which comes with a 0.375 Hz High Pass Filter. In most cases, the user sets another high pass filter to eliminate the low frequency components that are not needed. Crystal Instruments Spider-80X and Spider-80Xi systems are best suited for these types of applications.

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