four DAQ6070 with RT System running 4 data acquisition VI's taking too long time

[Venkat]

I am using four DAQ6070 in a RT System. Totally I need to acquiring 24 analog channels (6 for each card) for 2 Sec and I have 2 Sec to process it and stream it to hard disk. I am using hardware triggered acquisition to start the next acquisition. In RT dynamically I am launching four VI’s. Each VI will acquire 6 analog channels at 100KS/S (means each VI will handle one DAQ Card). Each VI will read the data for some time (300 ms) and will wait for some time and again it will read the data. This will happen for 2 sec. The data is stored in RT Stack and for processing I am using the stack. Now these VI’s are taking long time (10 S) and I found that it is because of AI Read VI and no
t because of processing and streaming to hard disk. To complete the acquisition for 2 Sec it is taking about 8 Sec. How I can reduce the VI timings?

[Kristi_P]

Hello Venkat,

As I understand your system, you have four separate VI's that are called on your RT System using VI Server. Each VI is configuring the acquistion, reading and clearing the acquisition. Each acquisition is started by a hardware trigger, for a total of four triggers.

If the total time is taking 8 seconds, it sounds like these operations are executing in serial rather than in parallel. Perhaps what you are wanting is to synchronize the start of all four acquisitions with one hardware trigger.

There's an example program that ships with LabVIEW called, "Two E-Series Shared Digital Trigger". This example will configure a finite acquisition on two boards, starting both acquisitions with the same digital trigger. The first AI Read will block ev
erything else until the two seconds of data is collected. It then will call the second AI Read which will not block because the data is already available in the PC buffer for LabVIEW to simply read. You might try running this example and modifying it for your 4 boards to see if you can get the desired performance.

Hope this helps.

Regards,

Kristi H
Applications Engineer
National Instruments