Using Spectral Analysis

Ultraprobe Tip

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1.  Ultrasound spectral analysis software lets you listen as you view your screen while the sound sample is played. You can observe the sound in the FFT (spectral) screen and in the Time Series screen to note any changes as it plays. Play the baseline sound, create an overlay, and compare one sound to the other. All the while you will hear and see the differences (if any) that will give you confidence in your diagnosis.

2.  You can’t be expected to remember the sounds of every component of every type of equipment you inspect. While you run through routes, the equipment you check often varies. One route might have a lot of pumps and motors, while another might include gears or valves and yet another switchgear and transformers. Even if you were to specialize in “only” bearings, there are many types, sizes, speeds and loads that can affect your diagnosis if you were to rely solely on listening. Being able to record a baseline sound sample and store it for future reference and analysis is invaluable. If in the future you should come across a change in dB or suspect a change in sound quality you can record that new sound and play it back in the spectral analysis software and compare that sound with the baseline sound.

3.  Data alone is not the answer. While it is true most bearing conditions can be detected by increases in amplitude, there are always anomalies that might not show a dB change at onset. There are also potential problems that cannot be trended through sound level increases but are more likely to be detected or noted as qualitative sound differences that can be heard but not fully understood unless viewed on a spectra or time domain screen. One area in which this is obvious is electrical diagnostics. While we can often identify arcing, tracking and corona, there are instances in which it is confusing as to whether or not a problem exists. Is it corona or vibrating component? Is it severe tracking? What about loose windings in transformers? Playing these back in spectral analysis software will enable you to better understand the condition and plan appropriate corrective action.

4.  Sound quality and decibel differences can be viewed simultaneously allowing you to compare both sound qualitative differences and decibel differentials on the screen. These differences can be analyzed in detail when, in the FFT (spectra) screen, the sound peaks and frequency content can be compared using the vertical and horizontal cursors. The time series can also be used for detail analysis with the aid of the magnifier tools to view any hidden information.

5.  As a “sound-based” technology, spectral analysis enhances our diagnostic capability to practically all the basic ultrasound applications: valve inspection & trending, bearings, lubrication issues, electrical testing (switchgear, transformers, motor control centers, insulators, busses, arrestors, etc.), gears, pumps (cavitation), motors, presses, compressors, steam traps, hydraulics, even specialized leak situations (heat exchangers, compressor valves).

If you are using spectral analysis, let us know what you are doing. Send us your story to share in upcoming newsletters & we’ll send you our thanks along with a valued UE hat.

If you have not yet begun to use spectral analysis, download the software from our website for an evaluation: http://uesystems.com/prod_software_spectralyzer.asp