Estimate AC/DC of a sine signal

[mhed]

Hi,

i capture an analog signal (a sine) with labview and i want to extract several informations from the signal like : Amplitude, offset, peak value, frequency, etc.

I almost get what i want, but i can't get the correct value of AC / DC components of my signal.

For example, i receive a signal like this one :

y = 1.25 + 1.25 * sin (2*Pi*3000*t).   

I except the following value :

f = 3000 Hz  (I got it)

Peak = 2.5 (I got it)

Ampl = 2.5 (I got It)

DC = 1.25 (I got it)

AC = 1.25    and there is the problem. I don't have this value.

Maybe i forgot a vi in my design, or maybe labview can't process this value or maybe i'm do it wrong because i don't exactly talk about AC value.

[johnsold]

Please define your terms.

What is the definition of the "AC" for which you do not get the value you expect?  It is not possible to determine what you want from your example because the value 1.25 is assigned to two different components.

Posting your VI would also help.

Lynn

[CarlosD]

I think that you are looking for the AC value without DC offset, right?

You can calculate DC value of the signal with a Basic DC-RMS module, rest this value from the signal to get a pure AC signal and calculate RMS value of this signal with another Basic DC-RMS vi.

I hope this solve your problem.

Carlos

[Jeffrey_Zola]

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@mhed wrote:

Hi,

i capture an analog signal (a sine) with labview and i want to extract several informations from the signal like : Amplitude, offset, peak value, frequency, etc.

I almost get what i want, but i can't get the correct value of AC / DC components of my signal.

For example, i receive a signal like this one :

y = 1.25 + 1.25 * sin (2*Pi*3000*t).   

I except the following value :

f = 3000 Hz  (I got it)

Peak = 2.5 (I got it)

Ampl = 2.5 (I got It)

DC = 1.25 (I got it)

AC = 1.25    and there is the problem. I don't have this value.

Maybe i forgot a vi in my design, or maybe labview can't process this value or maybe i'm do it wrong because i don't exactly talk about AC value.

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Look at the terms you reported and compare to your equation. There is a "DC=1.25" and an "Ampl=2.5" in your list. Your equation describes a sine wave with an amplitude of 2.5 units (peak-to-peak) centered at 1.25 units. I believe you are trying to solve for an extra term!

Jeff

[crossrulz]

You two do realize this thread was from back in January...

[Jeffrey_Zola]

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@crossrulz wrote:

You two do realize this thread was from back in January...

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And your point is what? 

Trying to get my post count out of newbie territory!