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Abstract

An apparatus for monitoring a vibrating structure, such as a bridge, uses multiple motion sensors spaced along the structure, each of which produces an analog raw data signal which is then filtered in anti-aliasing filters to remove substantially all frequency components of the signal above a selected cutoff frequency, f.sub.co. The filter outputs are connected to addressed inputs of an analog multiplexer which then multiplexes the signals in response to a channel address clock which repeatedly generates a sequence of channel addresses to scan the data input channels at the multiplexer corresponding to the addresses in the sequence. The complete sequence of addresses is repeated at a frequency of at least twice the cutoff frequency to obtain substantially simultaneous samples from the sensors so that data from different sensors may be correlated. The multiplexed signal is then converted to digital form and stored. The apparatus preferably also includes a fast Fourier transform processor to convert the data to the frequency domain and a means for calculating the response mode shapes for the structure from the frequency domain data.

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