delete group increase file size

[faustina]

In LabVIEW I create a TDMS file using DAQmx Configure Logging.  Since my users want to control when data is being written to the file, I make use of the Logging:Pause property.  Very often two groups of data are created in the TDMS file; one containing a few points (less than 20) and one containing the desired data (10000+ points).  In DIAdem, if I delete the small group and save the file with a different file name, the new file size increases about 4 times in size.  Why does this happen?  I would expect the file size in reduce by a small amount, but definitely not increase in size.  I'm using LV 2012 SP1 and DIAdem 2011.

[YongqingYe]

When using DAQmx Configure Logging to write data to TDMS files, the data is "raw data" directly from DAQ device, TDMS file format is specially desgined for this case to store the "raw data" so that the file size is smaller and the performance can be improved. When using DIAdem to delete some data and save the file, the new saved TDMS file actually stores normal data instead of the "raw data" so that the file size can be much larger than before.

[faustina]

So then if I have a very large TDMS file it is best that I write a VI in LabVIEW to reduce it the way I want (delete groups, extract portions of data, delete channels, etc.) rather than do that processing in DIAdem and save to another file.  I will always want to keep the original file created during DAQ.

[Brad_Turpin]

Hi faustina,

You actually can get DIAdem to save the data as scaled integers or SGLs instead of DBLs, but DIAdem will save everything as DBLs unless you tell it not to.  DIAdem will scale the integers linearly, though, whereas DAQmx has the ability to scale integers with polynomial scaling.

Brad Turpin

DIAdem Product Support Engineer

National Instruments

[cyk888]

I have the same problem, using DIAdem 2015 Service Pack 2. I have data recorded as TDMS from an NI DAQ. Using DIAdem, merely re-saving the data under a different file name increases the files size from ~400MB to 1.5GB. I added two channels to the data and the file size went up to 3GB. Is there any way to reduce the files size and how exactly do I do that in DIAdem? Manually or using a script? 

[TommyDunkz]

Hi cyk888,

Thank you for posting your observation to the discussion forum! For future reference, you will usually get faster support on the forums if you are posting a new thread, instead of posting to a very old thread.

I did some research on this issue and, while I wasn't able to find a definite answer, I did notice that you currently have a service request open with our Applications Engineering team to address this issue. Once you are able to come to a resolution, feel free to post a new thread documenting the problem and the solution if you have a few minutes--this will help others resolve the issue if they run into the same problem in the future.

Cheers,