TDM file with multirate interleaved data?

I am developing a datalogging application that samples several channels at different rates and I need a way to graph the data quickly. After figuring out that reading my own custom file format byte-by-byte takes a long time in LabVIEW, I started looking at TDM files.
I found the TDM Header Writer VIs, and it looks like I can just create a header that points to my binary data. However, I have several channels which can be sampled at different rates. For example:
Channel 1 data
Channel 2 data
Channel 3 data
Channel 1 data
Channel 1 data
Channel 2 data
Channel 1 data
Channel 1 data
Channel 2 data
Channel 3 data
Is it possible to create a header for data stored like that? Or would I need to include data for all of the channels at the highest frequency? ...
Channel 1 data
Channel 2 data
Channel 3 data
Channel 1 data
Channel 2 data (dummy)
Channel 3 data (dummy)
Channel 1 data
Channel 2 data
Channel 3 data (dummy)
Channel 1 data
Channel 2 data (dummy)
Channel 3 data (dummy)
Channel 1 data
Channel 2 data
Channel 3 data
I am thinking about creating 2 files: one for low speed data (0-100S/s) and one for high speed (100-1000S/s). I would simply insert the dummy data for channels that aren't the highest speed.
Am I going about this the right way? Is there an easy way to store the data the way I _really_ want to (all the channels interleaved without dummy data)? Any ideas or suggestions would be greatly appreciated.
Thanks,
John

John,
Have you considered splitting the data as it is acquired and writing each channel to it's own binary file and then using a TDM header file to relate the acquired channels?
That would be how I would approach this problem but as I haven't tried this before I can't tell you how successful it will be (yet).
I'll try looking into this some more and post again when I have some better information.
In the meantime here are some resources that you may or may not have seen:
Introduction to the LabVIEW TDM Header Writer VIs
LabVIEW TDM Header Writer VIs
Introduction to LabVIEW Data Storage VIs
~
Simon H
Applications Engineer
National Instruments

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Hey Atrina,
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Message Edited by AndrewMc on 01-27-2010 11:21 AM
Thanks,
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Attachments:
digitalconvert.vi ‏13 KB

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Hi rvillalta319,
Sounds like you'll need to adapt your code to use both a for loop and some implementation of the GroupCount variable (or ChannelGroups.Count) as seen here:
http://zone.ni.com/reference/en-XX/help/370858K-01/varoff/groupcount/

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i have a question regarding error handling, when using the nilibddc.dll.
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Solved!
Go to Solution.

Hi there,
thanks for the replies (and sorry for my late answer).
The code above is from a simple Visual C++ Project that i use to run some tests with the dll.
If i posted the question in the wrong topic please let me know - i found some other posts dealing with the dll so i thought i'm right here.
I attached a tdms and the corresponding "corrupt" tdms_index file.
The file handle stays 0 when i debug my code with that file and i receive the error -6211.
I want to use the dll as part of an application that runs as system service. It reads and writes information from/to existing tdms files. After the information is read the application moves the files. So, if the tdms_index file gets corrupt (by whatever) i have the problem, that the index file is locked as long as the service is running and the file can't be moved. I can't tell how often this happens (hopefully never) but if i can do something against it, i would like to integrate this precaution.
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Attachments:
samplefile.zip ‏3 KB

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Error reading TDMS file with inconsistend dt

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Attachments:
error-2501.JPG ‏198 KB

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Message Edited by TonP on 02-14-2007 07:45 AM
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TDM file with multirate interleaved data?

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