write measurement files filesize

[manuwestern]

Hello,

i record a lot of data from my plc and want to write it to a measurement file in tdms format.

the problem is the files are very big, if i use the "write to measurement file"-express-vi.

If i use the"TDMS Write"-Function instead the files are much smaller, with nearly the same settings.

Is there a way to use the Express-VI with the same effiency if i would use the "TDMS Write"-Function?

Why are the files so big if i the express-vi?

[crossrulz · Accepted solution]

In general, avoid using express VIs.  They tend to just be something that you can put down and quickly have something that will work.  They also tend to be inefficient.  In the case of the Write To Measurement File, it opens and closes the file each time you call it.  With TDMS, that causes a lot of overhead in the file.  If you did a TDMS Defrag on each of your two files, they should come out to about the same size.

[manuwestern]

Ok Thank you very much.

Just one last question, how can i rename the different signals in the tdms file? Now they are names "untitled x". I am looking for an elegant solution, because i record about 200 different Signals.

[crossrulz]

It looks like you can do that with the Set Dynamic Data Attributes.  One of the inputs is Signal Index and another one is Signal Name.  Using a FOR loop, you can create an array to set all of the signal names.

[manuwestern]

I doesn't work, or is it wrong?

[manuwestern]

Solution:

[crossrulz]

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@manuwestern wrote:

I doesn't work, or is it wrong?

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You needed to use a shift register to hold your Signals.  Then it keeps the values you added between iterations.