How ti save date/time info into .lvm

Question

Hi,
i need to save date/time info (Date:Time) into one .lvm together with my other signals (dynamic data). any suggestions?
it should look like this for example
results.lvm:
date/time signal 1 signal 2 signal 3
01.01.2005/12:00 2.2 3.3 4.4
01.01.2005/12:02 2.4 3.4 4.5
01.01.2005/12:04............
and so on for every loop.
thanx in advance
vedran divkovic

Answer 1

The LVM Express VI was designed to be easy to used. To facilitate this, data formats are fixed and cannot be set by the user in the Express VI. You have several options to get the format you want.
If you don't need all the header information in the LVM file, roll your own code. If you are only saving one line of code at a time, this is particularly easy. You will also need to write your own read code, assuming you are not just using Excel or something similar.
Use the formatting capabilities of your analysis program to create the date code. Excel, for example, is perfectly happy to generate a time/date string based on a simple number. You may have to convert from LabVIEW absolute time to Excel absolute time, but that is fairly trivial. You can make a macro to do this.
If you need the LVM header info, write the file using no data to get the header, then fill in your data with your own formatting. Read-back will be harder, since you will need to write that yourself. However, you can probably get most of the info from the LVM file read (maybe with an error), then read your own formatted data from the end of the file.
WARNING: this one dives into vi.lib code. While you cannot change the formatting in the top level of an LVM file, the subroutines do take formats on a per-column basis. So, you can modify the original code to do what you want. Open the front panel, then search for ex_SignalsToSprdsheetStr.vi. Give it the format string you want and you are off. Note that this format will be in place everywhere you use the LVM code unless you save the entire hierarchy to a different location (using Save With Options->Development Distribution, include vi.lib files). Be very careful with this. You can easily get into cross-linking problems (linking VIs from the wrong location).
One final comment. You can find the specification for the LVM file format in Specification for the LabVIEW Measurement File (.lvm), Version 1.0. It includes everything you didn't want to know about the LVM file format.
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