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Help : Lock-in VI

Hi..

I'm trying to measure very weak signals so, I use a chopper which makes
a reference signal for lock-in.
And measure a spectrum from weak light signals...

I don't know how to program a spectrum analyzer VI and Lock-in VI..

Please help me out..

Thanks in advance.

Jongseo
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1 You must measure simultaneously your reference signal and your weak signal
(VI AI Multi PT),
2 you must "center" your two signals (substract their mean)
3 you multiply "point to point" your signals, you obtain a signal,
4 then the result is the sum (or the mean) of this signal.
(after 2, you may too compute a "scalar produce" (produit scalaire in
french).
This result is proportionnal to the amplitude of the weak signal, multiplied
with the cosine of the dephasage between the 2 signals.
So this dephasage must be constant and different from pi/2

It is possible, but more difficult to calculate the amplitude and the
dephasage in all the cases.

TaeHyun a écrit dans le message :
38BF01EB.8254C81@ee.tamu.edu...
> Hi..
>
> I'm trying to measure ve
ry weak signals so, I use a chopper which makes
> a reference signal for lock-in.
> And measure a spectrum from weak light signals...
>
> I don't know how to program a spectrum analyzer VI and Lock-in VI..
>
> Please help me out..
>
> Thanks in advance.
>
> Jongseo
>
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