A stall precursor detector system for an axial flow compressor having at least one optical sensor to detect the deflection of a rotating airfoil of the compressor, means for comparing the deflection with a predetermined value, the predetermined value being indicative of onset of a stall in the compressor; and means for identifying onset of a stall and producing a stall onset signal if the deflection is greater than the predetermined value. A method for detecting a stall onset in an axial flow compressor system comprising (a) providing at least one optical sensor to measure the deflection of an airfoil, the deflection caused by a rotating stall cell; (b) comparing the deflection as measured in step (a) with a predetermined value indicative of a stall; and (c) identifying onset of a stall if the measured deflection is greater than the predetermined value.

A method and apparatus is provided for diagnosing and correcting rotating stall and surge in rotating machines by monitoring dynamic shaft precession and comparing this precession with a standard and altering the precession as the machine approaches a destabilizing condition when indicated by the comparison step. Axial vibration monitoring means is also provided for monitoring and comparing a dynamic axial vibration of the machine with a standard and altering the axial vibration as the machine approaches a destabilizing condition. Furthermore, the instant invention measures the complex dynamic stiffness of the machine and computes the direct dynamic stiffness and the quadrature dynamic stiffness for use as a destabilizing warning device by monitoring for a drop in direct dynamic stiffness and/or a coincidence of zero crossing of both the direct dynamic stiffness and the quadrature dynamic stiffness components. One embodiment for altering the rotating stall and/or surge is by a controlled active servobearing.

An eddy-current sensor having a thimble shaped alumina housing into which is positioned first and second coils wound about an insulating coil support. A Kovar sealing ring seals the alumina housing to a metallic base member to which is secured a protective tube carrying an electrical cable which makes electrical connection with the coils. A multifaceted nut secured to the metallic shielding of the cable nestles within a complementary shaped insulating member to prevent the cable from being twisted or withdrawn from the sensor thus maintaining electrical integrity.

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.