Variable Speed Machines

Variable Speed Machines from Tensor Systems Pty Ltd

By: Tensor Systems Pty Ltd  28-Oct-2014
Keywords: Vibration Monitoring, Vibration Transducers, Vibration Detection Controls

Condition monitoring variable speed machines using fixed period time sampling is acceptable if they only vary speed slightly as the vibration spectrum becomes only slightly “smeared”. If the machine 1x speed varies by +/- 1% then for an input shaft speed of 20.2658 Hz driving a gear with 19 teeth, the tooth meshing frequency, nominally 385.05113 Hz, will vary by the same % amount. If we have a spectrum of 3200 lines and 2400 Hz range (top spectrum) the 1x harmonic will fall on line number 27.0211 +/- 0.2702 lines which may not be noticed, but the tooth meshing frequency at 385.05113 +/- 3.8505 Hz will fall on line number 684.5353 +/- 6.8454 lines, ie it is “smeared across 13.7 lines” which for constant energy has the effect of reducing the spectral peak heights significantly. It’s 2nd harmonic will fall on line number 1369.0707 +/- 13.6907 lines, with double the smearing, which further reduces peak heights and also makes sideband recognition impossible, and the spectrum useless. detail at http://www.tensorsystems.com/variable_speed.html

Keywords: Condition Based Maintenance, Vibration Analysis, Vibration Detection Controls, Vibration Monitoring, Vibration Switches, Vibration Transducers,

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