A sensor array for nondestructively monitoring a structure to detect a critical event. The sensor array includes a plurality of discrete sensor nodes, each of the discrete sensor nodes producing an electrical signal in response to a structural event. In the preferred embodiment, the sensor nodes include a plurality of piezoceramic fibers arranged in a planar array in which the fibers are aligned substantially parallel to each other, each of the fibers having a plurality of polarized regions that are substantially oriented according to their polarity in either a series, parallel, or combined arrangement of series and parallel orientations, and an electrical interface connecting the plurality of polarized regions of each fiber in series with one another. A signal adder receives and combines the electrical signals from each of the discrete sensor nodes to form a single sensor array output signal. In the preferred embodiment, the electrical interface further includes at least one electrical bus substantially aligned with the fibers and a signal processing module for receiving and processing the single sensor output signal. The signal processing module is linked through the digital data bus to a central processing unit. The plurality of discrete sensor nodes may further be divided into discrete subgroups, each located at a different structural location to provide a degree of sensing and determining the location of the structural event. In the preferred embodiment, the discrete sensor nodes are electrically connected in series, thereby forming a continuous series connection between each of the discrete sensor nodes to improve the likelihood that a critical structural event will be detected.

An acoustic pick-up, particularly an ultrasonic pick-up for acoustically diagnosing machines, for example, for detecting leakage in valves or for diagnosing positions, comprising a piezoelectric measuring element and an electronic circuit that processes the measurement signal into a form that is suited for transmission to an evaluation device. In order that the acoustic pick-up can function without an external auxiliary power supply, means are provided by means of which auxiliary power required for operating the electronic circuit can be generated from the acoustic signal to be picked up.

A device for indicating a beat level L, the device including an analyzer which responds to a reference frequency .OMEGA. and a harmonic coefficient B to extract from an evaluation signal E a first acceleration signal .gamma..sub.B at a frequency equal to the product of reference frequency .OMEGA. multiplied by harmonic coefficient B; and a second acceleration signal .gamma..sub.B-1 at a frequency equal to the product of reference frequency .OMEGA. multiplied by the harmonic coefficient minus one; and it further includes a control circuit CC which receives acceleration signal .gamma..sub.B, .gamma..sub.B-1 to produce beat level L.

A sensor array for non-destructively monitoring a structure to detect a critical structural event. The sensor array includes a plurality of discrete sensor nodes, each of the discrete sensor nodes producing an electrical signal in response to a structural event. A signal adder is electrically connected to the plurality of discrete sensor nodes for receiving and combining the electrical signal from each of the discrete sensor nodes to form a single sensor array output signal. A signal processing module then receives and processes the single sensor output signal. In the preferred embodiment, the signal processing module uses the time interval between the electrical signals from each of the discrete sensor nodes formed into a single sensor array output signal to calculate the location of the critical structural event. Also, in the preferred embodiment, a data collection system is located downstream of the sensor processing module.

A distributed stress wave analysis system is disclosed for detecting structure borne sounds cause by friction. The detected information is processed using feature extraction and neural network artificial intelligence software. The system consists of stress wave sensors, interconnect cables, and preferably three modules: (1) distributed processing units, (2) maintenance advisory panel, and (3) laptop computer. A derived stress wave pulse train which is independent of background levels of vibration and audible noise is used to extract signature features, which when processed by neural networks of polynomial equations, characterize the mechanical health of the monitored components. The system includes an adjustable data fusion architecture to optimize indication thresholds, maximize fault detection probability, and minimize false alarms.