When setting up a vibration measurement, one selects a frequency range to measure (Fmax) and a resolution or "number of lines". The frequency resolution of the vibration spectrum is equal to the Fmax divided by the number of lines (and multiplied by the window factor - which we will ignore here for now). So, if we collect a spectrum with an Fmax of 1,600 Hz with 800 lines of resolution, the resolution on our plot will be 1,600 / 800 or 2 Hz. This means that if we have a vibration signal at 100 Hz and another at 101 Hz, we will not be able to see both of them because our maximum resolution is not small enough to resolve them. The two will appear as one peak.

When collecting vibration data it is important to first consider the frequencies one wants to measure and then select the appropriate combination of Fmax and resolution to capture and resolve the frequencies of interest. Why not just take as much resolution as possible? Because, it takes more time to collect the data and it takes up more space in the data collector.

Typical vibration measurements are taken with 800, 1,600 and occasionally 3200 lines of resolution depending on the Fmax.

Tip Provided by the Mobius Institute
www.mobiusinstitute.com