FFT real and imiginary not equal to magnitude

[koodave]

Dear All,

I am trying to collect complex pressure at a single point in a tube.

However, the magnitude i calculated using the complex results produced by the FFT function (square root of real^2 + im^2) did not match with the magnitude results i collected directly from the microphone (without going thorugh the FFT function).

Can i know what have i done incorrectly ?

"please see the attached for the overall block diagram"

Thanks,

Dave

[altenbach]

There is no way to tell by looking at a picture of the code, because we cannot see what's in the dynamic data wires and how the express VIs are configured. What are your units? For example you do the FFT on plain arrays, thus losing all information on timing that is typically contained in the dynamic data.

Can you create a example with simulated data that demonstrates your problem without the need of your hardware?

[koodave]

Hi Altenbach,

Thank you so much for the prompt reply.

I am trying to collect pressure readings in terms of pascal.

Actually i am writing four pressure readings at the same time (see the attached).

I attach my front panel and block diagram, together with some simulated results.

Please have a look on them.

Best Regards,

dave koo

[altenbach]

Last time I tried, I was not able to run a pdf document with pictures of the front panel and block diagram. It would be infinitely more useful if you could attach the actual VI instead.

[koodave]

Hi there,

Sorry for the inconvenience.

I was unable to attached more than three pictures just now, hence the reason why i attached a pdf file.

I will attach the VI in the new reply.

Please check the attached again.

Many thanks,

Dave

[koodave]

Dear Altenbach,

Here is the VI i used to record the pressure readings.

dave