Acquisition stops after a single Start Trigger and Reference Trigger

[pawlik]

We're using DaQmx and are trying to acquire repetitive samples using a Start Trigger and a Reference Trigger.  We are able to read the first acquistion , but when we attempt to read the next acquisition, we obtain error -200278, "Attempted to read a sample beyond the final sample acquired.  The acquisition has stopped, therefore the sample specified by the combination of position and offset will never be available."

It seems as though the acquisition is stopped by the Reference Trigger and is not restarted by the next Start Trigger.  Can anyone help?

  Thanks,

  Paul

[Raajit_Lall]

Hi,

Looks like you are trying to do retriggerable analog input.  This cannot be done directly on most DAQ cards.  If you do have a multifunction DAQ card, and have counters on that card, you can use the counters (which are retriggerable) to achieve this.  There is a tutorial on this topic.

The reference trigger is a stop trigger, so it does stop the acquisition and using a start trigger after the reference trigger without completely restarting the task will not work.  As mentioned in the tutorial below, you would be using the counter to generate the sample clock of the analog input acquisition.  There are also examples at the bottom of the tutorial.

Retriggerable Analog Acquisition in NI-DAQmx

Hope this helps.

Regards,

Message Edited by Raajit L on 07-03-2007 03:23 PM