Adding sine waves and using Fourier transform

[loudoe77]

My assignment is to generate two sine waves of differing amplitudes and frequencies, add the sine waves together, and perform the fourier transform on the added sine waves. When using the the FFT Power Sprectrum and PSD vi on my added sine waves, I am then supposed to be able to look at my waveform graph and locate the amplitude of the first sine wave at its specific frequency and do the same with the second sine wave. My problem is, when completing this operation I am getting max values at my two specified frequencies but the amplitudes do not match to their corresponding values. Does anyone know what i am doing incorrectly? Please let me know. Thanks

[RavensFan]

Read the help for the function.

A power spectrum does not give amplitude.  It gives an RMS value and is units^2/Hz.

It gives the square of the amplitude divided by 2.

[loudoe77]

Thank you, is there a VI that would output the amplitude rather than the RMS value? 

[RavensFan · Accepted solution]

There are several FFT functions scattered throughout.

One I found is called Amplitude and Phase Spectrum.  It puts out amplitude as RMS, but you can multiply that by square root of 2.

[Henrik_Volkers]

Nice assignment 😉  you can learn a lot on DFT.

while monitoring your DFT results, play around with the frequencies and the number points used by the DFT. ...   and be surprised by the effects of windowing 😄