Formatting LabVIEW Measurement File

[rattofest]

Hello,

I am using the DAQ Read and Write LabVIEW Measurement File Express VI's for a simple datalogging application. However, I would like to use absolute time (HH:MM:SS) as an x-value (or append it as another column to the .lvm file) and modify the file's header.

Is there any way I can do that while still using the Express VI's?

[DFGray]

If I remember correctly, the Express VIs specifically do not do that for performance reasons.  The full timestamp is listed in the header, then relative timestamps are listed for the X values (assuming you have them turned on).  Parsing the full timestamp for either read or write is a large time hit.

To my knowledge, you cannot do what you want to do with the Express VI.  However, you can roll your own fairly easily using the lower level text parsing.  If you like the LVM header, you can write your first line using the LVM VI, then write subsequent lines with your own code.  This will mean your first line will not be correctly timestamped, but you could also overwrite it, if you wish.

Another option is to post process the file.  This can be done fairly easily in LabVIEW and with a bit more difficulty in almost any other language or Excel (LabVIEW has timestamp functions you will need to reproduce elsewhere).  You can find the start of your data simply by looking for the ***End_of_Header*** line.  The original timestamps are in the Time line of the segment header.  You can get the complete LVM spec here.

Good luck.  Let us know if you need more help.