On-line shaft crack detector

Details On-line shaft crack detector On-line shaft crack detector

1993-12-21

1996-01-02

Williams, Hezron E.

Measuring and testing

Vibration

By mechanical waves

73660, 364507, G01N 2904

Patent

active

054798248

ABSTRACT:
A method and a device for detecting a circumferential or thumbnail-shaped transverse crack which has developed in a shaft connecting a driving component (motor) to a driven component (pump) and then estimating crack size. Crack detection and crack size estimation are performed while the machinery is operating. This shaft monitoring device will alert equipment operators that a severe problem is developing. The device will allow the equipment operators to estimate the operating time remaining before the equipment must be shut down for inspection and repair. The method utilizes measurements of fluctuations in the current and voltage in a three-phase induction motor to determine the time-varying motor torque. The computed time-varying torque is converted to the frequency domain using fast Fourier transforms and the rotating element torsional natural frequencies are determined. The torsional natural frequencies are also calculated using conventional finite element techniques for various simulated crack depths. The observed torsional natural frequencies are then compared with a table of calculated natural frequencies to determine crack depth.

REFERENCES:
patent: 4282756 (1981-08-01), Molnar

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