Many of the noise or vibration problems take place during a varying speed process. For example, the start up process of a turbine machine, the acceleration of a car engine or the operation of servo motors can create excessive noise and vibration but may be at normal levels at constant speeds. To measure varying speed noise and vibration, we need to perform special analysis called 「order tracking」 to see the problems at varying speed.
A simple example of 1x Order is the frequency of the once per revolution of the shaft that is rotating. The larger the unbalance of the shaft, the larger the amplitude of the first order as shown in a FFT Analysis. If you see a second order, this means that the event is happening 2 times per shaft rotation. A 12th order is an event that happens 12 times per revolution. Because machines have many events happening at different orders or times per revolution, it is important to have the proper analysis tool to help the user understand and properly measure during a varying speed measurement.
Benstone Instruments has spent significant engineering in the order tracking program to properly re-sample data digitally with respect to the tachometer signal. The patented algorithm ensures that the data measured maintains the same resolution and accuracy
In the order domain, no matter how the speed varies. This is very significant when performing order tracking analysis.
The result of order tracking analysis can be shown in different formats.
1. Waterfall or intensity plot :
The following figures show the map of a series of order spectrums which were taken during a coast down process. From the plots below we can see how the vibration of each order changes as the speed varies, and which orders dominate during the varying speed process.
2. Order trace plots :
The following figures show the plots of individual order traces versus rotation speed. Because each order trace contains phase data, we can show a trace on the polar plot, as illustrated in the right bottom figure. This information is very useful for engineers who need to study the dynamic behavior and resonance nature of the rotor as it passed through critical speeds.
Benstone Instruments offers the order tracking analysis program for Impaq Elite, Impaq and Fieldpaq.
Benstone Instruments, Inc. 32905 Northland Court . St. Paul, MN 55045 . 651-257-6500 . FAX: 651-257-4004 You are visitor #2764
