Abstract: A high-volume source for very low frequency applications in which conventional speakers are inadequate is disclosed. A presently preferred embodiment comprises a reservoir 32 with a pressure relief 33; a controller 34; a supply blower 36; an exhaust blower 38; a positive plenum 40; a negative plenum 42; an orifice plate with valving 44; a horn 46; and pressure transducers 48, 50, 52, 54, feeding detected pressure levels to the controller 34. An electrical command signal s(t) is also input to the controller. The command signal is a voltage analogous to the acoustic pressure or volume velocity to be output by the source.

Abstract: A system and method are provided for monitoring synchronous blade vibration in a turbo-machine. At least three sensors capable of detecting the arrival of each blade are arranged about the cylinder which surrounds the tips of the blades. The location of the sensors is selected to minimize the influence of errors in the data. To this end, and to simplify the installation of the sensors into the cylinder, the sensors may be non-uniformly spaced. The location of each sensor for purposes of constructing Fourier transforms is determined using the arrival times at the blades at each sensor, expressed as a fraction of a rotor revolution. The transform matrix is constructed for a predetermined discrete set of M harmonics, so that M harmonics are analyzed simultaneously, the number of harmonics which can be simultaneously analyzed is related to the number of sensors used.

Abstract: An on-line vibratory fatigue monitor measures displacement of an object such as the blade of a turbine rotor to generate a displacement signal and calculates accumulated fatigue in the object in dependence upon the displacement signal. The displacement of the object may be detected by passive proximity probes which generate signals indicative of changes in magnetic flux or capacitance between the sensor and the turbine blade. An analog/digital converter converts the signals from the probes to digital signals indicating displacement of the turbine blades. The digital signals are processed, preferably by taking a Hilbert transform, to detect the amplitude envelope and instantaneous frequency of the displacement. The amplitude and frequency are combined with steady state stress on the object to determine fatigue usage which is accumulated by constantly monitoring vibratory displacement and changes in the steady state stress.

Abstract: A nonsynchronous turbine blade vibration monitoring system is comprised of a maximum of two sensors circumferentially mounted along the turbine blade row for detecting the actual arrival times of the turbine blades at the sensors. Expected arrival times of the turbine blades at the sensors are determined and then compared to the actual arrival times in order to obtain turbine blade deflection data. Harmonic analysis is then performed on the blade deflection data to determine the level of vibration at each non-integral harmonic.

Abstract: A portable acoustic intensity measuring device comprising a pair of electroacoustic transducers at a positioned predetermined distance from one another. The measuring device utilizes analog summing, subtraction, integration and multiplier means for measuring an acoustic intensity vector midway between the two electroacoustic transducers. The acoustic intensity measuring device further comprises error correction means connected in circuit with a preamplifier means and a meter means. The error correction means includes switching means comprising a first switch connected in circuit with the preamplifier and summing means and subtraction means and a second switch connected in circuit with the multiplier and the meter for simultaneously switching the first and second preamplified analog signals at the summing input and subtraction input and for simultaneously switching the polarity of the acoustic intensity signal at the meter.