Hi Saridi,
From what I understand you�re trying to acquire data at a certain rate say X Samples/s and then you only want to record a subset of the data. For example if your logging rate is X/2 Samples/s you would only record every other data point returned by the board.
The data is returned by the DAQ Assistant as the dynamic datatype. What you�ll need to do is manipulate this data to eliminate the samples you don�t want to write before you pass this data to the Write LabVIEW Measurment File VI. You can convert the dynamic data type to a waveform which you can then manipulate using the Convert from Dynamic Data VI. If you double click on this VI you can choose the type of data you want to convert the dynamic data to. Once you have the data in th
e waveform type you can then extract the data from the waveform using the Get Waveform Components function. You will then have the data in the form of an array and you can use the Decimate 1D Array function to pick out every other (or every third etc) element. You then need to rebuild the waveform so that you can pass it into the Write to LabVIEW Measurement File VI. One thing to remember is the dt for this new waveform is different from the original because you only have half as many samples. Please take a look at the attached screen shot for an example of the method I just described.
I hope this helps!
Sarah Miracle
National Instruments
