Original Date: 03/08/1999
Revision Date: 01/18/2007
Information : Shaft Torsional Vibration Analysis
The Applied Research Laboratory at the Pennsylvania State University (ARL Penn State) uses shaft torsional vibration analysis to detect and measure minute torsional vibrations (twists) which occur during shaft rotation. The laboratory’s advances in this technique greatly enhance the ability to detect shaft and coupled load defects, which aid in characterizing the condition of machines and equipment.
When a shaft is turning at a constant speed, the modulated twist rate is so minute that it is undetectable with conventional sensory techniques. Traditional techniques use sensors to measure the flex and bend, harmonics, and torque of shafts. None of these have the ability to detect the minute changes in torsional vibration, especially when the shaft is operational and coupled to a load. The ARL Penn State developed an extremely sensitive measuring technique that uses a laser light source and a photosensitive transducer probe to read the encoded tape applied to a rotating shaft/coupler being measured. Information obtained from the probe is first fed through an analog incremental demodulator, and then a digital signal processor for presentation. The shaft torsional vibration analysis can also detect and measure the low frequency signal and amplitude that represents a fingerprint for a continuously rotating healthy shaft. When minute alterations occur to the shaft or coupled load, the fingerprint also changes.
Another significance of shaft torsional vibration analysis is its applicability to the condition based maintenance (CBM) community. Parameters which were previously nonexistent can now be analyzed. This technique not only detects minute alterations to the rotating shaft, but to the coupled load which may prove even more significant (e.g., in the detection of defective blades in turbine engines and power generators). Further refinement, analysis, and characterization are being pursued by the ARL Penn State to predict the specific defects occurring within a shaft and coupler system.
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