ODS vs. Modal Analysis (cont.)
Phase Analysis
Phase data remains a crucial turning point in the evaluation of data. As mobility or structural rigidity is not necessarily a constant on all axes considered (we wish !), a little wherewithal helps the expert in separating a mere misalignment problem from a bent shaft, a dynamic imbalance couple generated axial motion from a foundation problem, etc.
The various aspects or specialties of phase analysis, such as balancing, phase analysis, alignment precision fault detection, foundation analysis or bearing housing analysis, are all available under the Preferences button.
The various denominations refer to specific tasks, such as the proper ID of a cocked bearing, a phase analysis detection of a resonant condition, the multi-plane balancing procedure correction of an excessively vibrating rotor, looseness at or near the base, etc.
Amplitude
Amplitude is noted in displacement, mainly because this measurement is free of a time connotation (unless expressed as a displacement occurring at a given discrete frequency). From an ODS analysis point of view, the choice of units has little or no bearing on the end result, as opposed to adjusting one’s own “heuristics” or rules of processing the data when considering severity from an RMS context to a PEAK context, or a linear to VdB context.
In the context of structural, base or foundation analysis, one of the most important roles of amplitude (and one of the most neglected) is not one of absolute severity evaluation but rather one of comparison of what is there, and what isn’t ! The transmission of vibration or lack thereo is a powerful indicator of behavior as will confirm any pulp and paper engineer used to dealing with sole plates, or any centrifugal compressor expert dealing with bases.
Order
1 X RPM defines a frequency known as synchronous and also known as FIRST ORDER.
Even multiples of this frequency are known as second, third order, etc, meaning 2X RPM and 3X RPM. The notation is so widely accepted that the typical text will merely express 1X, 2X and 3X without further ado.
When there are various components operating at different speeds, it becomes an ABSOLUTE necessity to include which component is being referred to : MOTOR RPM and driven rotor RPM are rarely equal UNLESS the machine is direct drive.
A gear reducer will exhibit several RPMs according to which shaft is being looked at. Input is equal to motor speed, one or two intermediary shafts may show significantly lower RPMs as one progresses along the train and finally, the output RPM defines the last components’ first order.
These factors are not as yet important as FINE TUNE only offers the basic DIRECT DRIVE configuration, but the comment should serve in other areas of your PM program as well as in the near future (as other FINE TUNE configurations become available).
ODS vs.