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February 17th, 2015, 11:50 AM   #1
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Harmonic Calculation from Data Points

I should start by saying I haven't taken a calculus class in about fifteen years so anything you can phrase in layman's terms would be helpful. I have watched and read quite a bit on this subject online, but it seems every time they get to the calculations there is some assumed knowledge of symbols I either don't remember or never knew.

I am trying to take measurements from a cylindrical object and extract its harmonics from the rounded edge as it spins. I have a spreadsheet which is supposed to have done that by using the Root Mean Square averaging of the wave (cell D133 of link). However, I need to cut the root mean square step, and provide the actual harmonic values at each point. I don't really understand how this first harmonic was calculated well enough to make this happen. I do however understand the changes to the angles needed to calculate the later harmonics.

Here are the assumptions I am working with so far
-The average value is how much my collected data point deviates from the expected norm.
-The angle was calculated by taking 128 equidistant points across the 360 degrees of the object.
-The wave hits a peak point twice to complete one period, so the peak to peak can also be found by hitting the average X value twice.

Slightly fuzzy
-I thought the X and Y values are the traditional Cartesian coordinates of the first harmonic expressing the information in circular complex form. I am not so certain of this as some of the values don't make perfect sense. I am not super confident on the math used for these though I understand basic SIN and COS.
-The angle of the harmonic was determined by atan2 and letting the spreadsheet convert to degrees. I could use a little exposition here of what this really means other than it can be used in the formula to calculate the actual harmonic points in column F.

Main Problem
-How do I calculate the harmonic values without using RMS?

If you can clarify any of this, I would very much appreciate it.

If you would like to write directly on the reference spread sheet, feel free.

Thanks

Last edited by Czern; February 17th, 2015 at 11:54 AM.
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