Creating a Spectrum analyser

[J Haynes]

I'm new to Labview and am trying to create a spectrum analyser for use with a accelerometer providing an variable output of 1 volt/g. I'm using a 6024E Data aquisition card which works with other instruments. I'm having a few problems with the program i've created in that it doesn't give the expected spectrum (i've connected the accelerometer to a real spectrum analyser). I've looked at the various examples provided with labview but none seem to be able to offer any help. I've included the file and any help would be really appreciated!

Thanks in advance

[LocalDSP]

In a discrete measurement system, the Nyquist criteria requires you to sample your signal at a rate that is at least twice the bandwidth (or span) you want to measure. In praxis values like 2.50, 2.56 (or higher if oversampled) are used.
So when you expect your span to be 20 kHz you should sample at a rate of at least 2.5*20 = 50 kHz. The same story applies to your "number of lines", so if you request your measurement span to be 800 lines wide, you should acquire data blocks of 800 * 2.5 = 2000 samples.
I have modified your VI to reflect that. If needed you can change the constant value "2.5" to a higher value (like 5.00 or 10.0 depending on the board you are using) to reduce effects of aliasing on your measurement results.