save data to file at a slower sampling rate

[Crandall55]

This is probably a very simple question...but i'm a first time user and a student trying to complete a project.  I am using a USB 6008 to acquire an analog voltage signal continuously and view it on a graph.  I want to save the voltage data in a spreadsheet to be viewed later, but I would like to sample the signal only twice a second.  I am using version 8 student edition.  Any help would be greatly apprecitated  and if I have not provided enough information please ask. 

Jordan

[MehakD]

As a starting point, I would recommend you to look at the shipped examples that come with LabVIEW. You can find the shipped examples by looking under Help>>Find Examples>>Hardware Input and Output>>Daqmx>>Analog Measurements. This would be a good starting point for you.

I editted the Cont Acq&Graph Voltage-Int Clk.vi for your requirements. Please refer to the attached VI for the editted example.

I hope this helps!

[Crandall55]

Thank you very much and sorry for the delay in getting back to you.  I have a couple more questions.  Is there a way that I can strip the bundled data to just have the voltage because i don't need the timestamp as it uses too much memory for my low end DAQ.  I keep getting an error that data has been overwritten and is no longer available.  I would also like to slow the sampling rate down even more to 1 sample per second but still keep the waveform constant.  Thanks again

Jordan

[JeffOverton]

Under Cluster&Variant use Unbundle by Name to pull things out of clusters

[Crandall55]

I tried to unbundle the data but it is the wrong type of data i guess.  All I want to do is display the waveform and save the voltage in excel file at 1 sample per sec.  Thanks

Jordan

[MikeS81]

Hi jordan,

at the moment you have an array of waveforms, so to get one channel you have to index the array. To get the single elements use the "Get Waveform Components" function.

Mike

[Crandall55]

Thanks for the help that worked perfectly.  My only other issue is slowing down the rate that samples are written to the spreadsheet I only want to have them written once a second.

Thanks again,  Jordan

[MikeS81]

Hi Jordan,

you could insert a case structure and only write every 10th value to the file. The advantage is that you anyhow see all value in your Waveform.

Hope this helps.

Mike

[Crandall55]

hello again, thanks for the help i really appreciate it.  I couldn't seem to get the case structure to work properly, I've attatched a section of the program where i'm trying to do what you suggested.  Maybe you could implement the case structure to make it work.  Thanks again

Jordan

[RavensFan]

Yours is just reading in the whole array, and giving you the entire array back from the 0th row, 0th column.  The loop will only run once because the entire file is read at once and will hit the EOF in the first iteration.

Look at this instead.

Message Edited by Ravens Fan on 04-01-2008 12:16 AM