spectral measurements express: no averaging

[Caers]

I'm using the Spectral Measurements Express VI to make a frequency plot from an accelerometer connected to a PXI-4462.  Seems to work fine, with a nice frequency graph, except when I turn on 'averaging': no averaged signal appears, no matter what parameters I use for averaging.  Coupling an indicater to the 'averaging done' output shows that it never actually succeeds in getting an average.

Is there something else I need to turn on or so?

[Aaron_E]

Hi,

I'm an AE at National Instruments and will attempt to help you with your issue.

Firstly can I check what version of LabVIEW you are using?

One possible solution could be that you have not enabled averaging in the Spectral Measurements Express VI. To do this double click the Spectral Measurements VI and check the averaging box.

Please let me know how this goes and if you have already done this I will advice you further.

Regards,

[TrottM]

Hello Caers

The averaging done node only returns TRUE when the number of averages completed equals or exceeds number of averages. Have you tried reducing the number of averges you are trying to aquire? Also have you tried changing the number of samples you are making to see what effect that has?

Let me know how this goes and i'll look into this further to see what else you could try.

Matt

[Caers]

Thanks for the swift reply

LabView 10.0.1

and as you can see in the attached image, "Averaging" is checked

and if I leave "produce spectrum" at "only when averaging complete", I get no frequency graph whatsoever.

[Caers]

@TrottM:

doesn't matter - even if I put the number of samples at 20 with a sample rate of 2000, and the number of averages at 10, nothing happens

[Aaron_E · Accepted solution]

Seen as your reading in data from an accelerometer is it the frequency peak you are wanting to read?

Please find attached an example VI that calulates the the peak FFT average over the spectrum. You should be able to replace the Simulated Signal Express VI with a Daq Assist Express VI. The example calulates the RMS based upon the peak magnitude measurements. The file is a VI snippet which is saved as .png but will open in LabVIEW.

Try using this example to run your code, and let me know how you get on.

Regards,

[Caers]

ok, problem solved

typical beginners error: I used the "run continuously" button as a loop-generator, which didn't preserve the values for the averaging function of the spectral measurement.  Adding a "while" loop around the whole lot solved the issue.

Thanks!