DAQmx_WaveformGen/DAQmx_Scan: Running multiple at the same time

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Mon, 04/16/2018 - 02:37 pm

Hi,

I've an appliation where it would be beneficial to have multiple scanning/outputting operations running in parallel (on different channels of course). Basically I want to do some special data acquisition when a channel is idle and some other type if it is used.

Is that supported?
If not is that a NIDAQ mx driver limitation or an XOP limitation?

Thanks,
Thomas

PS: I'm using a PCIe-6343, http://www.ni.com/en-us/support/model.pcie-6343.html.
You can do multiple scans or waveform generations simultaneously as long as they are on different devices. In general, NI DAQ devices have only one clock so you can't do two simultaneous operations on the same device. That is a long answer for "it is a NIDAQmx limitation". Actually, I believe a hardware limitation, not so much a driver limitation.

John Weeks
WaveMetrics, Inc.
support@wavemetrics.com

April 16, 2018 at 05:14 pm - Permalink

This is no problem if you get a NI device that specifies simultaneous sampling. The PCI-6115 and PXI-6115 are two examples (I used the former quite easily for four channels with Igor's NI Tools). Most other multichannel DAQ cards use sequential sampling.

NI calls these S -Series devices. See http://sine.ni.com/nips/cds/view/p/lang/en/nid/10834

April 17, 2018 at 06:21 am - Permalink

Thanks Stephen I was not aware that simultaneous sampling does that. Unfortunately these devices only have two AO. And I also got the other device already ...

April 17, 2018 at 09:13 am - Permalink

With regard to "simultaneous" multi-device sampling, a potential complication lies in the precision you need for simultaneity. For example, different devices will have slightly different clock frequencies (i.e. one part in 10^4 to 10^6) and potentially different walk-off in the sampling times. In some extreme cases with long scans, you may want to force use of a common clock (as with a RTSI connection between devices). Also you might need a common hardware trigger input for precise starting, rather than relying on software scan initiation to the different devices.

April 17, 2018 at 09:53 am - Permalink