Modal Space - In Our Own Little World

I ran one test with an x-excitation and can see some modes and another test with a y-excitation and see some different modes. Could I use an oblique angle instead?

Well, that's a very good question. Its one that comes up often in terms of running modal tests with a shaker excitation. Of course it is totally acceptable to run one test with a shaker at some oblique angle to the structure. But the only thing we need to be careful about is to assure that we don't select the reference point at the node of a mode.

Let's talk about this a little more. Let's start this discussion with a simple structure that has mode shapes that are very directional in nature. Now just what do I mean by that. That means that the response of the structure is primarily in one direction with very little or no response in the other directions for a given mode of the structure. Yet another mode of the structure may have response in a different direction than the first mode with little or no response in the other directions.

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2019 IEST ESTECH Conference & Exposition - Las Vegas, NV

The 2019 IEST ESTECH conference was held in Las Vegas, NV from April 29 through May 2nd, 2019.  This year, Dr. James Zhuge provided a technical presentation explaining Crystal Instruments’ combined Temperature, Humidity, and Vibration (THV) Control system.  Dr. Zhuge provided the opportunity for attendees to gain first-hand knowledge regarding Crystal Instruments latest technologies offered for environmental testing systems. The Crystal Instruments THV system provides one convenient user Interface to set up schedules for temperature, humidity, vibration, and more.

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Running Multiple-Input Multiple-Output (MIMO) Vibration Control Tests Without a PC (Black Box Mode)

The capabilities of Crystal Instruments’ Spider devices are well known and the ability of the Spider to operate without a PC makes it advantageous for several applications, including vibration control.

Spider front-ends are powered by Texas Instruments’ digital signal processors and are capable of performing all the complex mathematical computations required for vibration control in addition to handling massive amounts of data for recording and frequency analysis. The full featured EDM software suite is a powerful tool for setting up the Spider system and for displaying raw and processed data. Once set up, the Spider can operate continuously even without a connected PC or in the event the PC crashes. This powerful operating mode (available to Spider systems) is referred to as Black Box mode.

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View Statistics Time History Signals in Vibration Control Software

Crystal Instruments recently released version of EDM 8.0 software allows users to view the selected characteristics (e.g., Peak, RMS or Peak to Peak) of a channel versus time for the entire duration of the test. This feature is included in all vibration control tests and allows users to track user-defined characteristics of any channel (including the control signal) for the duration of a test.

Users can conveniently customize this new feature by selecting the “Statistics Time History” tab of the “Measured Signals Setup” section of EDM. Once customized, the user can view the history of these signals by opening a signal at any time or the user can view the entire history of these signals at the end of the test.

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MIMO FRF Testing of License Plate

Extracting the natural frequencies, damping shapes, and mode shapes of a structure aids in improving the design of the unit under test. In this case, the modal characteristics of a license plate is acquired by performing a modal analysis.

A MIMO FRF test is carried out using a pair of modal shakers and 14 accelerometers to obtain the vibration characteristics. The shakers impart energy to the structure for a longer period, which ensures an increased data set. The higher quality of the measurements also aids in the better estimation of the modal parameters.

A roving response method is usually implemented with a modal shaker test, but this procedure induces a mass loading effect in the results. To avoid this, small uni-axial accelerometers are attached on all the measurement points to capture the response of the entire plate in one shot. To run the high-channel count test (14 response channels and 2 excitation channels), a pair of Crystal Instruments Spider-80X front-ends are used with a Spider-Hub. The latest 8.0 release of the EDM Modal software assists in executing the MIMO FRF test.

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Modal Space - In Our Own Little World

Could you explain the difference between time domain, frequency domain and modal space? I hear it all the time but I'm not sure what's the difference.

There's a lot to explain but let's start with something simple.

This question gets asked often. There's a lot of different aspects relating to this so let's start with a simple explanation without using too much math and explain all of this with a simple schematic. Let's use the figure to discuss all these different aspects of the time domain, frequency domain, modal space and physical space. Now there are a lot of parts to discuss in the figure, so let's take them in pieces - one at a time - and then summarize everything at the end. You might also want to remember the discussion we had before when you asked me about what modal analysis was all about ("Could you explain modal analysis for me?") to help with the discussion here.

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Poly-X, the Poly-reference LSCF Implementation and Experiment

Abstract
A poly-reference least-square method for modal parameter identification of a system in frequency-domain is discussed and implemented. It can also be considered as a multi-reference frequency-domain implementation of the recognized time-domain based Least-Squares Complex Exponential (LSCE) estimator.  The main advantages of the Poly-reference Least-Squares Complex Frequency-domain estimator (p-LSCF) are its capabilities of handling high system orders and high modal density. The stability diagram is much cleaner which makes the selection of system poles easier. Other advantages are lower computational times and the ability to handle multiple references. The Poly-X is Crystal Instruments’ version of p-LSCF, which is included in the EDM Modal software package. A MIMO FRF experimental test is carried out to demonstrate these advantages.

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Announcing Crystal Instruments’ new distributor, Avenir Technologies FZE for the United Arab Emirates, Saudi Arabia and Kuwait region

Crystal Instruments (CI) is excited to announce Avenir Technologies FZE as our new distributor in the United Arab Emirates region. Avenir Technologies FZE is located in the UAE, with offices in Dubai and Abu Dhabi.

Avenir Technologies is a value adding technical distributor providing high performance test & measurement products along with advanced technological solutions for the vibration market. They have extensive experience in providing solutions for military organizations, research labs, engineering teams, manufacturing companies, and the oil & gas industries.

Avenir Technologies also offers installation, field service and calibration with their delivered test systems.

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