Dear Sir,
Thank you for using the Developer Exchange.
The "Harmonic Analyzer" and "Power & frequency" VIs will always produce different results because they use different methods of calculation.
The Power & Frequency VI does an estimation of the power peak taking into consideration the information available in the adjacents frequency bands, being so you should have values closer to the values returned by the Harmonic VIs when you selected smaller values for the span, for example: 0 or 1.
Besides that the unit of the output of the functions is also different, it is in V^2rms for the Power & frequency VI and it is in Vrms for the Harmonic Analyzer VI.
Harmonic Amplitudes is the array of amplitudes of the fundamental component and its harmonics.
These values are always positive and are in units of Vrms if the input Auto Power Spectrum values are given in V^2rms
I hope this answer your question.
Best Regards,
Omar De Andrade - Applications Engineer
National Instruments
