How to change data type of daqmx logging

[MichaGue_01]

Hello,

I am using "DAQmx configure logging.vi" to stream the data of my continuous asquisition (6133, 8 channel, 2,5MS/s each channel) to may harddisk. This works well, only the resulting filesize is enormous.

Is there a way to change the data type of th tdsm stream from double to single?

Thanks a lot.

Michael

[MichaGue_01]

Just another question. When I open the tdms file in excel, there are a lot of cells with no information (see attached screenshot, red text). Is there a way to fill this cells with information?

Thanks.

[MichaGue_01]

All good things come in threes - My tdms files a around 500-1000MByte big. I want to read a part of a tdms file. Is there a way to read a part, e.g. start index position: 1000, length 10000 samples, without reading the whole file first?

Abstract of the 3 posts:

Post 1: Is there a way to change the data type of the tdsm stream from double to single, while using "DAQmx configure logging.vi"?

Post 2: How to fill the possible informations inside a tdms file with text (see picture of posting 2)?

Post 3: Is there a way to read a part of a tdms file without reading the whole file first?

Thanks for your help.

Michael

[Bob_Schor]

Well, you didn't attach your VI (not a picture, but the VI itself) so we can't "poke around" in your Write to Measurement File Express VI to see how you set it up and to make specific suggestions there.

You are writing out a whole lot of data.  The TDMS format is binary (which tends to be smaller than text-based formats), but also has "extra stuff" to facilitate getting specific data back quickly.  If size is an issue, you might want to consider doing a different kind of file I/O.  I know NI has a good discussion of the pros and cons of the various File I/O methods -- probably somewhere in Help.

Another point is that the Express VI requires a Dynamic Data (Signal) input -- even if you try to wire an Array of Singles into it, it adds the "Convert to Dynamic Data" VI to thwart you.

You can, however, "roll your own" and configure the TDMS files yourself (using VIs from the TDM Streaming sub-Palette.  This will definitely allow you to save the data as Sgl, and will explicitly allow you to define and fill in all of the Header Information that you want.  It is a bit of a challenge, however ...

Bob Schor

[crossrulz]

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@Bob_Schor wrote:

Another point is that the Express VI requires a Dynamic Data (Signal) input -- even if you try to wire an Array of Singles into it, it adds the "Convert to Dynamic Data" VI to thwart you.

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Bob, you really should read more closely.  The OP clearly stated that they are using the DAQmx Configure Logging, which is NOT an Express VI.

[crossrulz]

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@MichaGue_01 wrote:

I am using "DAQmx configure logging.vi" to stream the data of my continuous asquisition (6133, 8 channel, 2,5MS/s each channel) to may harddisk. This works well, only the resulting filesize is enormous.

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Assuming doubles are stored, that is ~160MB/s.  Yep, that will get large very quickly.

I want to say there is a way to store the raw A/D data (U16), which you could then convert to engineering units on your own.

You should also try to perform the TDMS Defrag on your resulting file.  That will likely do some compressing of the data (eliminate unused allocated space) and fill in some of your missing data.