Collecting Data from Multiple Parallel cDAQs

[aolima]

Hi,

I'm trying to build a VI to continuously collect cata from multiple cDAQs in parallel and am running into errors of it not being "able to keep up with hardware acquisition". I have 4 cDAQs total (2 of these are daisy chained). I've used a similar system before and after some adjustment to Rate and Samples to Read managed to get it stable but this time I have not been able to.

I've build separate acquisition tasks for each of the sources in my topology (daisy chained cDAQs are treated as single) inside the same loop. I've managed to narrow it down to the issue happening when I'm attempting to save the data into a file (using the Write to Measurement File VI). However I have not been able to figure out how to deal with this problem. Any tips on what I could try? A few of the things I've looked into:

• Producer/Consumer architecture
• Convert all my DAQ Assistant VIs into DAQmx tasks (done and still having same issue).
• Looked for other methods of saving data into a file that do not use the Write to Measurement File Express VI but not found one that worked.

I've try to post the actual VI I currently have soon (in a separate PC) but want to at least see if I was on the right track. I've included a snippet of a VI I built to demonstrate the layout of my other VI.

Thanks in advance for any thoughts.

[santo_13]

The only solution - please ditch all these express VIs, learn DAQmx drivers, data acquisition architecture, data logging and implement.

[mcduff]

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@aolima wrote:

Hi,

I'm trying to build a VI to continuously collect cata from multiple cDAQs in parallel and am running into errors of it not being "able to keep up with hardware acquisition". I have 4 cDAQs total (2 of these are daisy chained). I've used a similar system before and after some adjustment to Rate and Samples to Read managed to get it stable but this time I have not been able to.

I've build separate acquisition tasks for each of the sources in my topology (daisy chained cDAQs are treated as single) inside the same loop. I've managed to narrow it down to the issue happening when I'm attempting to save the data into a file (using the Write to Measurement File VI). However I have not been able to figure out how to deal with this problem. Any tips on what I could try? A few of the things I've looked into:

• Producer/Consumer architecture
• Convert all my DAQ Assistant VIs into DAQmx tasks (done and still having same issue).
• Looked for other methods of saving data into a file that do not use the Write to Measurement File Express VI but not found one that worked.

I've try to post the actual VI I currently have soon (in a separate PC) but want to at least see if I was on the right track. I've included a snippet of a VI I built to demonstrate the layout of my other VI.

Thanks in advance for any thoughts.

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As previously said, don't use Express VIs. The built in logging feature of DAQmx is quite efficient; it saves to a TDMS file. I highly recommend using that method. In addition, if the number of points you write to the file is an even multiple of the file block size, it becomes extremely efficient.

[aolima]

Thanks you both for your thoughts.

I understand that using DAQmx coding is much more efficient and have been trying to learn more about how to use that.

Here is the current VI I've been working on. Each cDAQ is in a separate loop and currently trying to save to it's onw file (if I could save them all to one that would be GREAT, but separate files is not the end of the world since they are already not time synced to each other..).

I've not figured out completely the save part so would appreciate some tips on what i'm missing there,

I've also attached the topology of my setup in case that helps,

Thanks in advance!

[santo_13]

Maybe you could benefit from DAQmx channel expansion technique, please describe all about the modules you've and how they are connected together.

[aolima]

Thanks Santo_13,

I've looked a little into that but am having a hard time trying to find a way to combine the data before adding that to the TDMS file...

I currently managed to make it work with saving to separate files (see VI attached), but was hoping to combine the outputs into a single array before saving it to the file.

As for the hardware I'm using, the topology image I shared previously (attached here again) lists all modules/cDAQs i'm using at each locations as well as how they are wired. In summary I have 4 ethernet cDAQs and 1 USB cDAQ with a 9237 and 9213 modules in each to reach Full Bridge strains and Temperatures at each location.