4474 data acquisition

[wilddog]

I am using NI PCI-4474 to acquire 800 data points every 100 miliseconds after triggered via PFI0.(Sampling rate was 10kHz.)  But it takes longer than the supposed time; it takes much longer than 50 seconds when I took 500 repetitions.  In case of 500 repetitions, it has to be done within 50 seconds (500 * 0.1 sec = 50 seconds).  But when I took ONLY 300 data points, it is okay.  I have no idea why these two show different results because both are still inside the limit (102.4kS/sec)  Thank you in advance.

[enderWiggin10]

Hi wilddog,

We are already working on this issue through email support.  However, I will echo the email.  You are completely clearing and creating your task for every iteration, which can take up to 200 ms, software and OS dependent.  In your case and per your math, you only have 20ms for the task to be cleared and recreated and eb ready to receive the trigger.  You will miss triggers and forece the acquisition to wait another 100ms.  This is why we recommend to use retriggerable analog input, not possible on your 4474 but it on all X-series multifunction cards such as the PXIe-6363, or to only start and stop the task within the loop.  Further, you should commit the task before entering the loop and starting.  This will downlaod all of the information onto the card and the the device will be ready to run; now when you stop, you will go beack into the commit phase and be able to start even faster.  I have went ahead and created a VI snippet of the code I suggested i nthe email.

Here is the code you should use: