How do I get the Frequencies out of the Dual Channel Spectral Measurement VI?

[eke14]

New user to 8.2. I finally have the real and imaginary output in ascii spreadsheet. I need the frequencies now. And then csv... for STAR Modal. Sigh.

[GovBob]

I really don't understand your question but I will make some suggestions. Since you are working with an express vi you are working with the Dynamic Data type. On the Express function pallette under the Signal Manipulation pallette is the from dynamic data type vi. This will convert your data to something you can use. For example you could convert it to a waveform type of data and extract multiple tone.vi for frequency information.

Hope this helps

[eke14]

I think I don't know what Dynamic Data is. I keep getting a message about it. If I convert to a waveform, can I separate two channels from one daq board? And do I need to name them as virtual channels? So many vis! Thanks GovBob.

[GovBob]

Which DAQ board are you using? I think you would use the split signals vi to get your seperate channels. I personally shy away from using express vi's as using DAQmx is not very hard to use once you get used to it and you don't have to convert from the Dynamic Data type. See here if you are using DAQmx and want to get away from the "canned" express vi's.

[eke14]

Thanks again. I had found that page but I can't decipher Task Out from a virtual channel. How do I know what kind of data/output/stuff is coming out of a wire? (I am using a CompactDAQ with 2 channels.) Also, about the first question, if there is no out wire except task out... Dual ch spectral measurement plots Magnitude versus Frequency. But if I convert it and export, I only get Magnitude. I can't get the x-axis - is that the same problem as waveform export, 2 channel, or 2D array?

[Dennis_Knutson]

If you convert each output of the spectral measurement to a waveform data type (or 1D waveform data type), you can use the Get Waveform components function to get the dt - in your case it's actually df. With a t0 of 0, and the dt, that is how the x axis is displayed.

Actually, you don't need to get the dt from both since they will be the same.

If you continue to have problems, just attach your code.

[GovBob]

In addition to Dennis's great advice. Use the context help (Ctrl+H). Use the example finder under the block diagram help>>Hardware Input and Output>>DAQmx>>Analog Measurements>>...Voltage>>Acq&Graph Voltage-Int Clk.vi is a good place to start.

Use the add attachments button at the bottom of the Reply to Message page to include your code or at least an image of the block diagram (.png or .jpg...no bitmaps please).

[eke14]

I've been trying to fix - I can post terrible block diagrams tomorrow. Dennis, thanks. I can convert the "dynamic data" to find the df, but the initial frequency says it is in "time stamp" form. Looking for converter now... GovBob, thanks, but I don't have that example vi. Odd. I opened the similar TDMS vi which uses "analog 1d wfm Nchan Nsamp" but I don't have that vi either. Geez.

[eke14]

Here is my terrible code. I noted all my current (not amp...) issues. Ha. I hope this attaches...

[Dennis_Knutson]

Seems to me that you are making things much more complicated than it needs to be. If you take the output of the merge signal function and wire it to a Write to Measurement File instead of the Write to Spreadsheet File, you will have everything you need. The df will certainly be there. Not sure how the start frequency will be written but if it's a timestamp, when you read it back and display it on a graph, you would set the graph to ignore the time stamp and it will start at 0.