Displaying amplitude vs frequency for entire time history in a spectra data view?

[benstan]

Hi!

I'm trying to create a spectral graph of some acceleration data that I have acquired. However I can only display the Spectrum at t=x. I want a chart/display that shows the magnitude of the acceleration vs. frequency for the entire time history!? I believe I was able to do this once but can not duplicate the results.

On similar note, I also would like to view the entire time history, on the order of minutes to an hour, of an amplitude vs time data view display. Changing the chart samples from the default 512 to some large number doesn't work and neither does changing the chart x axis range from auto to some value in the properties window of the chart.

Thanks for any help you can give me

[--Chris]

Were you possibly performing a sweep and then accumulating the spectrum of the acceleration as part of the sweep?  Displaying this accumulation on a view would show the spectrums for each iteration of the sweep.

As far as changing the history length, what were you setting the length to?  Changing it to something other than 512 should work.  Also, the history length only works for single point data and not waveform or spectrum data.

Could you possibly attach your project file so we can get a better understanding of what you are doing?

[benstan]

I was acquiring acceleration data from an ICP accelerometer. The data is coming from a test unit mounted to a shaker table. One of the data signals is also being split and supplying the shaker controller's feedback.

Exactly, I want the accumulated spectrum for the duration of the vibration test. This typically 1 hour.

I ran a logarithmic sweep from 4.8 Hz to 525 Hz at a rate of 1 oct/min. The log is about 13 min. and 16 seconds long. So my trial length is 796 sec. I've tried the chart history option, currently at 3980000. I guess since I want to view spectral and waveform amplitude this is not going to work.

I tried to atttach my .seproj file but it is not a valid extension. How else might I send this Signal Express project file to you?

[--Chris]

You should be able to attach the project using the "Attachment" control below the reply area.  Look below the gray area below the Submit Post option.

See circled area in the attachment of this reply.

[benstan]

I tried to use the attachment feature but .seproj files are not allowed. I get an error and it will not send the attachment. Do you want a screen shot??

[benstan]

Here, I was able to attach the file as a zip. However the .seproj extension should be added to the approved file type for the attachment feature.

[Brian_R]

So are you trying to find the frequency response of an object at a given frequency and then plot that for the entire frequency sweep? 

[--Chris]

I have two solutions that should work for you.  Both are not ideal, but will hopefully work until we add spectrum history to the product.  I have attached a project which shows both solutions.  The first solution is a live computation of the spectrums and the second creates the spectrums for a log.

In the live spectrum case we are using a sweep loop to accumulate the spectrums and then we can display all of the spectrums at once.  You need to configure the sweep to have as many iterations and your test and you need to sweep some parameter of a step.  You do not need to sweep a parameter of the DAQmx step but you need the DAQmx step to be in the loop.  Once everything is configured you should use the "Run Once" button to run the project.  You can still log the DAQ signals for later use by right clicking on the signals and select "Record While Running".  And once the spectrums are obtained you can create a snapshot of the spectrum accumulation from the Edit menu to keep it permanently.

In the second solution we are sweeping the Power Spectrum in the playback Work Area.  Again we are sweeping a dummy parameter and just using the sweep for accumulating the spectrum.  You again need to configure the sweep to have the correct number of iterations, but here you can go to the playback options tab (Turn on from the View menu) and it will display the number of iterations in the log.  There is one bug I found with this solution.  The first iteration of data is not always processed by the Power Spectrum.  If this solution is preferred, I can look into creating a patch for this issue.