Impact Excitation Processing for Improved Frequency Response Quality

Abstract

Impact excitation is the most common excitation type for measurements of frequency response functions for modal analysis and other purposes. The method used is almost always based on setting the data acquisition system up with triggering, fixed FFT analysis settings, and then using an accept/reject step where each impact is either accepted if the impact seems good, or rejected if it contained some error such as double impacts or overload. This method has several drawbacks that often lead to non-optimal frequency responses. In this paper, an improved method based on time recording of all signals and subsequent post processing is proposed. The data acquisition part is made easier with the proposed method, while at the same time the importance of a skilled operator is reduced. It is shown on a real test structure that the quality of the resulting frequency responses can be significantly improved (measured by the coherence function) compared to the traditional method, and at the same time the total acquisition time can be shortened. An automatic optimization procedure which allows for fully automated post processing is proposed.