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Improved Driving Point Measurements with a Coincident Mechanical Impedance Head Sensor

1997; Volume: 3089; Linguagem: Inglês

David M. Lally, David L. Brown,

Structural Health Monitoring Techniques

With the increasing popularity and reliance on experimental modal analysis as a product design and testing tool, test engineers are continually demanding a more accurate estimation of the modal parameters. Consequently, there has been greater emphasis placed on obtaining high quality, highly reliable data. One facet related to this task involves accurately determining the driving point measurement. (The driving point measurement requires the input force and response acceleration to be measured at the same point on the test structure.) This measurement contains useful information for estimating data quality and is required for deciphering the modal parameters during data processing. Currently, the driving point measurement is often acquired by using separate force and acceleration sensors placed in close proximity. The obvious problem with this method is that the information is not being taken at the same location. Thus, the coupling between the two sensors greatly affects how well the measurement was estimated. Previous attempts to rectify this situation have resulted in devices which include force and acceleration sensors in the same housing. Commonly known as mechanical impedance head sensors, these devices have traditionally suffered from poor performance characteristics and have been unable to fill the role required by today's advanced testing laboratories. To rectify the aforementioned issues, this paper documents the design, development and test results from an improved coincident mechanical impedance head sensor. This new device features force and acceleration sensing elements that are co-located, thereby, insuring a true driving point measurement. Furthermore, advancements in the microelectronics industry and improvements in piezoelectric design technology have resulted in additional benefits such as low dynamic mass, compact packaging, high stiffness and superior signal to noise ratio.