LabVIEW measurement file time data

[bsteinma]

I am writing data to a .lvm file and my time column is starting at 0 and going to 899 and then resets itself to start over (i.e. if I am acquiring 1500 data points it is going from 0-899 then 0-599).  I would like it to be continuous and go from 0-1499.  Can someone help me determine how to do this?  I don't know if it has something to do with my acquisition rate or the graph itself.  I am acquiring the data and outputting it to a waveform graph.

Also, in searching for the answer to my question I was interested in doing something else.  I would like to keep some of the information in the file header but much of it is useless to me.  I would like to just keep the comment column and an overall timestamp of when the data collection occurred.  Is there any way I can remove the rest of the information in the header.  The thread I was reading is located here http://forums.ni.com/ni/board/message?board.id=170&message.id=237804&query.id=878515#M237804 and they are opening the front panel of the write to measurement file subVI.  Can I manipulate or remove some of these items from there?  Another thread talked about writing a new subVI altogether to allow for more customization.  I don't know how to do this but wouldn't mind labeling the columns and moving the comment to another location.  Is there any particular vi someone would recommend starting off with?

Thank You,

bsteinma

[Anna_K.]

Hello, That is strange behavior, are you using the Write to Measurement express VI? what is the source of your data? is the data being overwritten?

[bsteinma]

Hi Anna,

I was able to narrow the problem down after talking with an Applications Engineer on the phone.  I am using the Write to Measurement Express VI.  The problem was within the DAQ propterties itself.  I had to change the timeout value under the advanced properties tab.  The problem hasn't been completely resolved however.  I may call NI again or see what I can come up with on here.  I am now able to get larger segments, however, it seems that the segment length depends exclusively on the number of samples to read in the DAQ properties.  I can set the number of samples to read to a very large valur but then the buffer is very large and I have to wait quite a while for the data to be written to a file.  I have my signals being output to a waveform chart so this greatly affects the refresh time.  If I set the number of samples lower then the refresh time of the graph is good but I get lots of segments of data.  The data isn't being overwritten.  The data is continuous despite the segmentation.  The only thing this has an effect on is the X Column values corresponding to time.  I have this set to one column only in the Express VI properties.  I receive values of 0-whatever in this column before they start over.  The AE I spoke with on the phone was receiving an actual timestamp that was not being segmented.  I could manually change these values each time I need to analyze a set of the data but this will become very tedious.

Thank You,

bsteinma

[Anna_K.]

Hello,

what do you do with your data before writing it the measurement file? I have tried a little trick, namely if the data is a waveform data type, I used the Append Waveforms.vi before passing it to the write express VI so that it thinks this is one continuous waveform. If you could post the section of your code between acquisition and write, we could see if such a fix  could work for you as well.

[bsteinma]

Hi Anna,

Here is a screenshot of my block diagram from the DAQ Assistant to the Write to Measurement File vi.  I'm not sure why it wouldn't let me paste the screenshot below so I've attached it separately.  I believe the only manipulation of the data is done when I am scaling it and a couple of times when it is being converted to a different data type.  Other than that I have a few graph waveforms to display my data.

Thank You,

bsteinma

[Anna_K.]

Hello,

Are you acquiring the same number of samples for each signal? Also, why do you convert from Dynamic Data only to convert back to Dynamic Data? What type are you converting to in these conversions?

[bsteinma]

Hi Anna,

While constructing the block diagram these conversions were automatically assigned.  However, I originally had the write to measurement vi in a loop.  I'm not sure if this had anything to do with it but I'll try to reconstruct those wire segments and see if it still prompts me to make these conversions.  I am acquiring the same number of samples for each signal.  I'm not exactly sure what type I am converting to in the conversions but will check and post back when I am on the computer with LabVIEW.

Thank You,

bsteinma