External sample clock and PCI 5124

[Adrian_Bradu]

Hello. I may ask something impossible, but it deserves a try ...

Basically I would like to use an external sample clock with my NI 5124 digitizer. Everything is OK when I use as an external clock a function generator at a fixed frequency (>50 MHz - the 5124 only accepts sample clocks from 50 to 210 MHz). In the real world, my external clock has got a variable frequency, from around 20 MHz up to around 150 MHz. However, I am not interested in sampling all my data, but only some, more or less 1/2 (the first half). The external clock corresponding to the useful data is still variable but with a small variation around 100 MHz, where my digitizer should be OK.

Do you think that it's possible to only sample some data using the external clock ?

Thanks for your help.

Adrian  

[S.Limb]

Hi Adrian,

As I understand you have an NI 5124 and an external clock and are wanting to acquire some data.

Have you looked at the examples in LabVIEW help? There are two examples that show acquiring data with an external clock, so this will help you with the architcture and structure of your program.

You can navigate to these through Help>>Find examples>>Hardware Input and Output>>DAQmx>>Analog Measurements>>Voltage in the voltage folder the Acq&GraphVoltage-ExtClk.vi example and Acq&GraphVoltage-ExtClk-AnalogRef.vi example. I hope these will be of some help when developing your application.

In the specification of your device is some information on external clocks, I recommend looking at this to ensure your external clock is compatible with the device.

I also have a VI that takes 100 samples from the target, but only reads one to display on the front panel or log to a file if that is what you want to do with the data. An image of that is added to this post.

If you need any more examples or information or have any further questions please don't hesitate to ask.

Thank you

Stephanie L

[dansch]

Hi Adrian,

Unfortunately, the digitizer is not meant to be able to use a variable rate sample clock due to some of the hardware implementations. While this is usually possible on most of our DAQ devices, as Stephanie pointed out above, it will almost always return a hardware clocking error on the digitizer as soon as the frequency changes beyond a normal tolerance for the board (45% to 55% duty cycle tolerance). Best of luck,