Multiple DAQ devices: DAQ assistent and daqmx

[Garp1]

Hello all,

I am trying to make measurements with NI PXIe-6356 and NI PXIe-4492. I would like to use one VI for this. Attached is my script. Unfortunately it is not possible for me to record the measurements at the same time. This means that when I start the VI, first the measurement from the DAQ assistant is recorded, and then the 8 channels. Is there a way to synchronize both? Thanks for your help.

[santo_13]

1. A strict NO to DAQ Assistant - you already are using DAQmx drivers, use the same for both instruments
   
2. You're trying to synchronize a DSA instrument and a Multifunctional instrument - there are some challenges and limitations of such synchronization due to difference in architecture
   • DSA uses a Delta-sigma ADC with a free-running clock
   • Multi-function devices derive the clock from PXI
3. The easiest option is to put all the channels (from both 6356 & 4492) in the same DAQmx Task (same type of tasks) and let DAQmx take care of the synchronization
4. The long route is for you to learn the synchronization methods and adopting them
   https://www.ni.com/en-us/support/documentation/supplemental/10/synchronization-explained.html

[GerdW]

Hi Garp,

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@Garp1 wrote:

Unfortunately it is not possible for me to record the measurements at the same time. This means that when I start the VI, first the measurement from the DAQ assistant is recorded, and then the 8 channels.

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Surely you can run the measurements from both devices in parallel!

The problem is: you programmed them to happen sequentially!

Use AutoCleanup to see the reason for that sequential behaviour…

(Another case of THINK DATAFLOW!)

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@Garp1 wrote:

Is there a way to synchronize both?

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Be as clear as possible with your questions!

Do you want to synchronize both devices - or is it sufficient to run both measurements in parallel?

In case of synchronization: how accurate do you want to sync?

Do those devices offer PFI lines to sync them?

[Garp1]

Thank you very much for the answers.

I tried this with a second DAQmx, it still does not work.

  

I get the following error message.

With other VIs (for example with the additional use of a bridge) I can simply switch these in series, and it works. It concerns also here a second card which is installed in the chassis. So I do not understand why it does not work here.

So I am not so well versed in Labview and measurement technology in general. Please excuse me if I have expressed myself a little unclearly. What I am trying to do is: I would like to make measurements over a certain period of time (which I can set in my VI) with a certain Sampling Rate (specifically 96 kHz). The measurements should start and stop at the same time.
Is there any way I can use the sampling clock to synchronize my two physical channels? Or would it possibly work with two DAQ assistants?

Thanks for the help.

Regards
Garp

[Garp1]

so quick update: I managed to get the measurement to run. Unfortunately they are not 100% synchronous.

The PXIe 4429 has a PFI 0, the BNC 2110 has some at 'Digital and Timing' and then additionally at 'Trigger/Counter' a PFI 0 (PXIe 6356). But I'm not sure if this is necessary, because both PXIe are installed in the same chassis.

thanks for the answers and help

[santo_13]

Both cannot be 100% synchronous - this has to do with the fact that both are different architectures one being a sampled clock and the other being oversampled clock.

You can achieve a certain level of synchronization by configuring them to reference clock and using Start triggers.

Please refer to the topic "Synchronizing between Sample Clock and Oversample Clock Timed Devices" in the link - https://www.ni.com/en-us/support/documentation/supplemental/10/synchronization-explained.html

Here they propose to export the sample clock of DSA to drive the 6356 - but beware there are Cons to this method

[Garp1]

Hi again,

Thanks for the answers.

I have already been on the website. But unfortunately that did not help me much.

Apart from my original idea to combine a DAQassistent with a DAQmx, I don't really understand why the two cards can't be synchronized with two DAQmx. I mean, it all works actually. Only I have a slight offset. Is there no way to connect the two sample blocks? Or would I need a digital trigger? How would I trigger the trigger or which of my PXIe would trigger which. First of all, I don't understand exactly how to do this. Which inputs do I use on my BNC, my PXIe 4492 has only one PFI0 socket. Even with the solution above I do not get further. I have tried that, but the data are still not synchronous.

In addition, I would not know where in my code the blocks belong (of which I also do not know which ones to use).

If someone could help, I would be very grateful. Many thanks for the answers and the help.