Timing in accquiring data

[kebitmat_f]

Hello,

I'm using PCI-6071E.

In my project, i set ScanClock = 19000 (hz), NScans =1000 and using hardware trigger with frequency = 8Hz.

In my calculation :

time for accquiring data= NScans/ScanClock = 0.05s

time between 2 accquiring data = 1/8 = 0.128 s

=> all the data will be accquired before start another accquiring data.

But, it's seem not correct ! Maybe time for accquiring data is longer because when i reduce NScans =10, my programe run well.

May be i misunderstand the way to calculate timing above ?

[John_P1]

Hi 145,

The problem is that Analog Input tasks are not retriggerable on older hardware.  Re-arming the task requires a software call, during which time you are evidently missing trigger signals.  Counter tasks are retriggerable however, and can be used to generate an external scan clock for your AI task.

By using two counters, you can achieve retriggerable AI like in the following example:

Retriggerable Analog Input using Two DAQ-STC Counters

The above VI is pretty dated (LV 5.1).  If your situation allows, I'd highly recommend switching to NI-DAQmx--the Traditional DAQ driver is no longer in active development and does not support any new models of NI hardware (or the latest OSes like Vista and Windows 7).

Here is an example that implements the retriggerable analog input task in DAQmx that will work on your E Series:

Finite Retriggerable Analog Input Using Digital Trigger

For a bit of extra information, X Series DAQ boards support native Analog Input retriggering and do not require the use of the counter workaround.  You would just need to set the Retriggerable property to "True" on your Analog Input task if using one of these boards.

Best Regards,