Modal exciter and modal excitation parameters from operating data continue to gain acceptance in the technological community. Testing in this manner is sometimes referred to as experimental analysis (EMA). It became a force in the 1970’s when computer-based analyzers began using Fast Fourier Transform. Before that, analog equipment was used. Estimation is a key step in Fast Fourier Transform based analysis. The step is also called curve fitting. There are several methods available and plenty of research documenting the different approaches and methods, as well as the effectiveness of each. The analysis is used to characterize vibration in the machines being used. This vibration is defined by three parameters, frequency, damping value and mode shape.

Two of the most recent approaches to testing include relying on a carefully controlled multi-shaker and one that believes artificial methods are not required at all. Both of these approaches rely on parameter estimation. It is important for a company to determine which method will work best for them and why.

Factors involved in making a choice include time, physical constraints and budget limitations. It also matter what you intend to do with the data that is ultimately produced from the testing. The two most common uses of the data are fixing noise and vibration problems and confirming the validity of element models. This data is used to develop new machines, products and structures. The data can be used to estimate possible strains on a structure and help designers determine how at risk a structure might be.

Usually, the preferred method is to measure the forces and use the artificial methods. The assumptions required for measuring the forces are less restrictive this way. If the forces are not known or cannot be measures, the operating data might still prove useful, if curve fitting is used later in the process. The operating data, which is the data acquired while a machine or structure is undergoing vibratory testing, is used to predict the outcomes of how a structure will operate will operate. In addition to operating data, shape data is also used. Shape data is produced when vibration occurs at two or more points on the tested structure.

Other testing methods include observing mode shapes and testing structural resonances or weaknesses. Structural resonance is the natural frequency at which a structure will absorb energy and vibrate excessively. Observing mode shapes is an earlier method of testing and uses the resonant property of a structure. Users are actually able to see mode shapes by using a strobe light test that is straightforward and easy to perform. The structure is vibrated with a shaker and an illumination is triggered by the movement. This leads to the surface to be still, while displaying the data at that frequency. If the vibration is then adjusted, the data will be dominated by the shape and be in close approximation to the mode shape. In many cases, each of the methods is used for testing. Most testing solutions are based on the desired development and use of a structure.

Author Bio: Penny Lane recently met with an engineer who could explain the use of a modal exciter and its benefits. She was impressed with the modal excitation technology.

Category: Business
Keywords: modal exciter,modal excitation