Proven Condition Monitoring Solutions

Vibration Data Collection

Vibration data collection is becoming more important to conscientious aircraft operators. By monitoring vibrations levels we can assess if the condition of our aircraft and its components are deteriorating and if component failure is imminent. It is often required to collect vibration data for several components that have close frequency values such as with engine accessories (generators, hydraulic pumps, oil pumps etc.).

If, for example, the operator is looking at components within a 21500Hz to 22000Hz frequency range, traditionally a signature range such as a 0-30kHz would be used, often displayed with a very low resolution of a 400 line FFT. In this case a resolution of 75Hz is achieved. The problem is that all components having a frequency that falls within the same 75Hz band will not be distinguishable from the FFT, and the vibration amplitudes from each component will be summed together to form a single spectral line on the FFT as in the diagram below. From this the operator is unable to decide which component is the cause of the high vibration levels and may be close to failure.

Even if the equipment has a higher number of lines for the FFT, say 1600 lines, the resolution is only reduced to 18.75Hz and the same problem will still exist for some of the components. The data collection time will also be increased as a consequence of the increased number of lines on the FFT.

Other than providing the ability to display the FFT with 6400 lines, Helitune has a useful method of solving this problem. It is possible to vary the start and end frequencies of the vibration signature anywhere within the range. As can be seen from the diagram below, a specific 21500Hz to 22000Hz frequency range has been created for the task. Even with a simple 400 line FFT a resolution of 1.25Hz can be achieved which would allow the individual components to be represented on the FFT by their own spectral lines with true amplitudes. Helitune also has the ability to display the FFT using up to 6400 lines which would achieve a resolution of 0.078Hz, enough for use on the most complex of assemblies.

In real life Helitune create vibration signature ranges at the optimum frequency range and number of lines on the FFT to produce the best possible resolution for the task and the shortest possible data collection time.