USB-6251 and 10 MHz external timer

[Ventus]

Hi, all.

I have USB-6251. Is it possible to make analog data acquisition with 100 kHz sampling rate by using external 10 MHz timer as a reference clock (or timebase or something else)?

[GarPar]

Hi Ventus-

      Sure!  This can be done by wiring your external clock source to any of the PFI lines and specifying your timing source as that PFI line.  Take a look at the Shipping example named "Cont Acq & Graph Voltage-Ext Clk.vi".  You can find this from LabVIEW by clicking on Help»Find Examples and then navigating to Hardware Input and Output»DAQmx»Analog Measurements»Voltage.  This VI demonstrates how to use an external clock for your acquisition.

     I hope this helps.  Best of luck with your application!

[John_P1]

Hi Ventus,

It sounds like you're actually asking whether you can use the DAQ card to divide-down the external 10 MHz timebase to achieve a 100 kHz sample clock, rather than using an external sample clock.

Indeed this is possible as well.  Unlike the PCI or PXI equivalents, the USB 6251 doesn't take an external reference clock (i.e. PLL) since it doesn't have any RTSI connectors.  However, instead you can use the 10 MHz clock as your AI Sample Clock Timebase.  The following image from the M Series User Manual shows a functional block diagram of the AI timing:

               

Programming in DAQmx, you just need to tell the driver what the rate and source of your timebase is, and the driver will select the divider for you based off of the desired sample rate:

           

Be sure to pick Sample Clock Timebase, not Master Timebase (E Series Only) or Reference Clock (Not Available on USB M Series).

Best Regards,

[Ventus]

Hi Gary and John.

Thank you for your answer. I really wanted to know how to divide-down external timer frequency. The last way works good.