I know you are addressing LabVIEW Experts, which I assume means those who have sufficient psychic powers that they can visualize the LabVIEW Code (the actual .VI file) that you failed to attach for us non-Experts. We'll just "guess" at what you are doing and suggest ways to improve it (sight-unseen, but "you get what you pay for").
I gather that you do not know much about FFTs, how it works, what "leakage" means, etc. A typical "power-of-2" FFT has 2^n terms -- two are "special", the "DC" term (which is exactly the arithmetical mean of the data) and the "noise" term (which is "what is left over when you have fit the remaining 2^n-1 terms). The other terms are pair-wise representations of harmonics of a sine wave whose period is the sampling period, so if you sample for 1 second, the harmonics will be 1 Hz, 2 Hz, 3 Hz, ... 2^(n-1) - 1 Hz.
If you are writing LabVIEW code to collect data and do an FFT on it, and you don't understand what you are seeing (and don't understand what you are doing), especially if you don't have "real data" to test, write a (very small) LabVIEW program that generates some data (there are Waveform Generators on the Waveform Palette, or you can simply try making a sine wave, or a square wave, or a triangle wave) and feeding your "signal" into an FFT. You can "experiment" by doing such things as:
- See how varying the sampling frequency changes the units of the FFT.
- See how varying the total sampling time changes the units of the FFT.
- See how varying the total number of samples (these three tests are different, but related!) changes the units of the FFT.
- What happens if you add a DC Offset to your signal? How does that change the FFT?
- What happens if you add "noise" (like "Sine + random number")?
- What happens if you apply a digital filter before you run the FFT?
You can learn a lot by doing this, and because you are doing it, it will "stick" with you better than if some "expert" tries to explain it to you (particularly if you can't ask questions and get answers quickly).
Bob Schor