Calculating the Required Lines of Resolution for Better Analysis
Calculating the required lines of resolution (LOR) is crucial for separating close frequencies in motor analysis. The minimum LOR can be calculated using the formula LOR = 3xFmax/(f2-f1), and analysts should be familiar with these calculations and analysis techniques.
Calculating the required lines of resolution is very important to separate close frequencies (for example 2X and 2xFL in 2 pole motors to identify the possibility of mechanical or electrical problem).
In the shown example, multiple spectra taken with different combination of Fmax and LOR.
The minimum LOR can be calculated from:
LOR = 3xFmax/(f2-f1)
At 400 Hz Fmax, f1 = 119.3 Hz, f2 = 120 Hz,
LOR = 1714 or more. At 1600 lines the two frequencies just started to appear, at 3200 I got full separation and 6400 lines will give one step higher (if you like quality data!).
It is good to check the calculations for the standard route setup (4250 Hz, 3200 or even 12,800 Lines) and realize the impossibility to separate those frequencies.
That is one of the reasons why many people will take two spectra per point, one of them is low Fmax and high LOR. There are also other options to handle such cases.
Category II analyst should be familiar with such calculations and analysis.