amplitude

[adobefree@gmail.com]

HI   GUYS :

        I have a question about the amplitude measurement , for example , i read the waveform from the sound card ,then use

 signal anayse vi to get the RMS, amplitude, freq and so on , but  i have noticed that , the RMS or amplitude can't equals to the real world physical voltage value directlly , what can't i do? if i want to get the real voltage amplitude like a multimeter

Thanks

Message Edited by adobefree@gmail.com on 11-10-2009 03:23 AM

[Norbert_B]

FFT, fast fourier transformation returns the effective value of each frequency contained in the signal. So the amplitude should compute to be a value of about 1/sqrt(2) in comparison to the actual maximum amplitude of the sinewave.

hope this helps,

Norbert 

[Coq_Rouge]

Then working with sound input the data is "normalized to a full input range equal to +/- 1. So you must calibrate your data. Also remember that a sound card can not measure DC. Sound card is for AC only with a range from ca 10Hz and up

[adobefree@gmail.com]

Hi：

      thanks for all your replay , it seems that sound card is not so professional , is there any other solution? i mean , i was heard about some PCI data collection card from NI , is that suitable for my requirement?  i just want to get the real peak value or amplitude of a AC signal

thanks