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Time Synchronous / Simultaneous Data Acquisition DAQmx PXIe-4492 PXIe-4497 in single National Instruments 1073 PXI Chassis (Legacy based)

Asked by usr0815 on 6 Mar 2014
Latest activity Edited by usr0815 on 6 Mar 2014
Hello,
I have a PXI System of National Instruments (NI) - type NI PXIe-1073 and two Data Acquisition Cards, which ought to be installed in the PXI-System (type PXIe-4492 (8 channel) and PXIe-4497 (16 channel)). My MATLAB and Data Acquisition Toolbox Versions (MATLAB R2011b, 3.0) are compatible with the cards and the legacy based acquisition setting, which I plan to use. The problem is the synchronization. I use something like 20 different Transducers (some AC-coupled, some DC-coupled), which I want to acquire, and, which is possible with the 24 channels of the two cards added together.
So far to the setup - now the "problem":
How can synchronize the two devices so that the data acquisition is virtual time-synchronous? I've found an article about synchronization of input and output via RTSI but it does not really seem to fit to my problem: http://www.mathworks.de/de/help/daq/examples/synchronizing-analog-input-and-output-using-rtsi.html
On the other hand I suppose that using the "start" function with start([ai1,ai2]) won't be synchronized, because the commands can't be executed at the same time and there might be a delay of some miliseconds (which the article above states clearly by an example with input and output sync).
The resulting question is: Does someone know how to start a data acquisition task on several NI-PXIe-Devices in the same PXI-Chassis really synchronously in legacy mode?
... and a somehow related and therefore resulting question:
If there is a possibility --> what happens to the successive samples after the trigger? - if I set up both cards to Fs = 48000 and then start an acqusition with a recording time of let's say 20 minutes - will all samples be controlled by the "same clock" (that was triggered at the start) or do the two cards use different clocks and there might be a varying delay between those? I just thought about this because there could be a reference clock in each card and depending on the accuracy of each reference - the signals could start to divergate from each other...
Thanks for your help in advance,
Philipp

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