Save data to tdms and lvm formats. TDMS file currently has additional data groups with decimated data ?

[mclarge]

Hello,

 

I have (8) accelerometers connected to (2) CompactDAQ 9233 modules. I need to acquire data from these 8 channels at 50 KHz for one second once an hour. I am using SignalExpress (SE) Version 3.5.0. I set up the 8 channels of acceleration in Max under one DAQmx task with continuous samples at 50 KHz and 50K samples to read. I imported this task into SE under the Tools menu and under Tools > Options I set “Automatically export log to text file” to YES.

 

These are the Recording Options I set up for the 1 second (50K samples), once an hour interval:

 

I used Date/Time start condition with “hourly” schedule start time and 1 hour interval, start logging immediately, and set “Repeat start/stop cycle” until a date about 6 months later. I left the advanced timing at (0) seconds. I used a stop condition of duration of 1 second, again with advanced timing set at (0) seconds.

 

Everything works fine, the loop stores one second data every hour, it writes a TDMS file and the corresponding text file. However, I don't like the format of the text file, I would much prefer the usual .lvm format with the one header and one X column (time) for all channels. The text file SE is currently writing has the channel names on top of the data columns, but also shows the time when the data directory was created by SE in these column headers. I don't like that, I would just like to see the channel names. So, how do I set up SE so that it creates the .lvm file format with the one header and one X column ?

 

Also, in the TDMS data file, there are 6 additional data groups with “decimated” data that provide no additional information. How do I set up SE so that it only writes the 50K data into one group without additional data groups in the TDMS file ?

 

Thank you for any assistance.

[Tanya_V]

Hello mclarge,

I don't know if you have already looked into this option for saving data, but there is a step that you can add called 'Save to ASCII/LVM' (Add Step»Load/Save Signal»Analog Signals»Save to ASCII/LVM). This may give you the data format you are looking for.

As for your second question, could you post your SE project so that I can get a better idea of your data and how it is currently saved?

Have a great day!

[Phil_J1]

Hello mclarge,

For your first item regarding the header information being listed in the exported file. The problem you're running into is as follows:

Because each chunk of 50K points that is being written to the text file has a different start time (t0) since the chunks are not contiguous, a new header is being created to include this information. Sadly, using the suggested Save To ASCII/LVM step will give you the same issue. The reason there is that the LVM header at the top of the file includes the number of points written to the file. If there was only one header, it would say 50K (which is how many there were when first written out) when there would actually be much more after more than 1 loop.

For your second question regarding the extra traces in the TDMS file, you are correct. These are traces used by SignalExpress for viewing. The best way to not have those generated is under Tools >> Options. In the "Logging" section, under "Miscellaneous", look for "Prepare log data for viewing" and set that to "Never". Note that you will not be able to view the new created logs in SignalExpress at this point. And if you try to, you'll be prompt to prepare the log for viewing, which will  generate these traces in your file.

Phil