Methods and systems for isolating a frequency in a rotating machine

1. A method of isolating a frequency in a rotating machine including at least one sensor, said method comprising:

receiving, from at least one sensor, a sensor signal that includes at least one frequency;

converting the sensor signal to a digital vibration signal;

modifying the digital vibration signal to generate a first envelope signal;

reducing a bandwidth of the first envelope signal before resampling the first envelope signal, wherein reducing the bandwidth of the first envelope signal includes down-sampling;

resampling the first envelope signal at a rate proportional to a rotational frequency of the machine to generate a second envelope signal; and

transforming the second envelope signal into a frequency spectrum to isolate the frequency.

2. A method in accordance with claim 1 , further comprising filtering the first envelope signal by applying an anti-aliasing filter to the first envelope signal.

3. A method in accordance with claim 1 , further comprising reducing a second bandwidth of the second envelope signal.

4. A method in accordance with claim 1 , wherein transforming the second envelope signal to a frequency spectrum comprises performing a Fast Fourier Transform of the second envelope signal.

5. A method in accordance with claim 1 , further comprising displaying the frequency spectrum in multiples of the rotational frequency of the machine.

6. A method in accordance with claim 5 , wherein the machine rotates at a variable speed, said method further comprising correlating a current speed of the machine with the first envelope signal.

7. A method in accordance with claim 6 , wherein correlating a current speed of the machine with the sensor signal further comprises generating a timestamp for the first envelope signal.

8. A method in accordance with claim 1 , wherein resampling the first envelope signal comprises:

post-processing the first envelope signal; and

resampling the post-processed envelope signal to generate the second envelope signal.

9. A method in accordance with claim 1 , further comprising receiving machine speed and timestamp information from a speed sensor, wherein the machine speed is correlated with each sample of the first envelope signal.

10. A monitoring system comprising:

a machine comprising at least one rotating component;

at least one sensor configured to detect a frequency of said at least one rotating component;

a memory configured to store data received from said at least one sensor; and

a processor programmed to:

receive, from said at least one sensor, a signal including at least one frequency;

convert the received signal to a digital vibration signal;

modify the digital vibration signal to generate a first envelope signal;

reduce a bandwidth of the first envelope signal before resampling the first envelope signal, wherein reducing the bandwidth of the first envelope signal includes down-sampling;

resample the first envelope signal at a rate proportional to a rotational frequency of the machine to generate a second envelope signal; and

transform the second envelope signal into a frequency spectrum to isolate the at least one frequency.

11. A monitoring system in accordance with claim 10 , further comprising a display, said processor is further programmed to display the frequency spectrum on said display.

12. A monitoring system in accordance with claim 11 , wherein said processor is further programmed to display the frequency spectrum in multiples of a rotational frequency of said at least one rotating component.

13. A monitoring system in accordance with claim 10 , wherein said processor is further programmed to reduce a bandwidth of the second envelope signal.

14. A monitoring system in accordance with claim 10 , wherein said at least one rotating component rotates at a variable speed.

15. A monitoring system in accordance with claim 14 , wherein said processor is further programmed to correlate a current speed of said at least one rotating component with the first envelope signal.

16. A monitoring system in accordance with claim 10 , wherein said processor is further programmed to:

post-process the first envelope signal; and

resample the post-processed envelope signal to generate the second envelope signal.

17. An analysis system, comprising:

a memory configured to store data received from at least one sensor; and

a processor programmed to:

receive, from said at least one sensor, a signal including at least one frequency;

convert the received signal to a digital vibration signal;

modify the digital vibration signal to generate a first envelope signal;

reduce a bandwidth of the first envelope signal before resampling the first envelope signal, wherein reducing the bandwidth of the first envelope signal includes down-sampling;

resample the first envelope signal at a rate proportional to a rotational frequency of a machine to generate a second envelope signal; and

transform the second envelope signal into a frequency spectrum to isolate the at least one frequency.

18. An analysis system in accordance with claim 17 , further comprising a display, said processor is further programmed to display the frequency spectrum on said display.

19. An analysis system in accordance with claim 18 , wherein said processor is further programmed to display the frequency spectrum in multiples of a rotational frequency of a drive shaft of a rotating machine.

20. An analysis system in accordance with claim 17 , wherein said processor is further programmed to correlate a current speed of a variable speed rotating machine with the first envelope signal.