Signal detection with cross correlation

[Elargus]

Hi
I am working on a project that consist of measuring the spectral noise density of a resistor and I need some help with that.
Presently this is how I've going about it.
1- I have the voltage noise out the resistor going through two low noise preamplifier in parallel.
2- take the output of the low noise preamplifiers and put it into two differential analog inputs of a PCI 6250
3- From labview 7.1, I use the crosscorrelation express VI and get the cross correlation of these two inputs. This should enable me to get rid of the nouse signal from the low noise amplifiers since they are uncorrelated and leave me with only the square of the noise signal from the resistor
4- then FFT the output of that to get the spectral noise density of the resistor.

Now this is the problem I am having the resulting spectral noise is not correct; I know this because know th4e resistance of the resistor I can compute the thermal noise out it and it should be: 4KTR(A^2) where A is the gain of my preamplifer. I am therefore trying to track down where this error is comming from. I noticed after reading some threads on crosscorrelation that its output is normalised. Could this be my problem? Is there a way to solve it?
Sorry for being this long but I thought I should give as much details as possible.
Thanks

[Ryan_V[DE]]

Elragus,

It sounds like your data acquision is functioning correctly. Perhaps this question could be better answered on the LabVIEW forums. It would also help if you posted your results and an example of what you believe a correct result would be. Please link that post in this forum for future reference.

Thanks,

[Elargus]

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regards