DAQ Series M Sample Rate and Number of samples

[Duffy2007]

Hello Clint1000,

like crossrulz wrote the internal buffer can be the maximum size of your RAM, because you can set this size per default the values described in this KB are used

How Is the DAQmx Buffer Size Allocated for a Finite or Continuous Acquisition?

[Clint1000]

Thanks..and thanks Duffy2007 for the link.  I always thought that the default values in Labview were the max the user could obtain.

[Clint1000]

One more thing..Is there a minimal amount of time you should acquire data for??  I had  400 hz waveform I was trying to read using 4k sample rate and 1000 samples.  The response, in another thread,  was that wasn't quiet enough  That would only give me 10 samples per waveform.  To me that's  enough but to someone knowledgeable it wasn't.  Is there a rule of thumb?? I know you want the max but what is the min I should try and obtain?

[GerdW]

Hi Clint,

To me that's enough

When you get your results with the required accuracy then it is ok!

what is the min I should try and obtain?

Well, as Nyquist and Shannon say: you need atleast twice your max signal frequency…

[crossrulz]

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@Clint1000 wrote:

That would only give me 10 samples per waveform.  To me that's  enough but to someone knowledgeable it wasn't.  Is there a rule of thumb??

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10x is my general rule of thumb.  But it really does depend on your requirements.  Especially with today's computers, more data is typically better.  You just have to watch your memory requirements.

[Clint1000]

So all these questions started because of sampling rates.  It looks like I need a simultaneous sample card. A PXI4340.  But I need 4 of them because I have 4 groups of 3 that I need measured simultaneously.   Next question:  What is the delay between each card??  is that a windows thing so its not accurate?? 

[Duffy2007 · Accepted solution]

Hello Clint1000,

multiple modules can be synchronized by selecting the PXI Express backplane 100 MHz clock as the reference clock source for all the modules, each Card then make a PLL to the backplane. The delay is then in a nS range

Page 25

http://www.ni.com/pdf/manuals/377014a.pdf

Synchronization Explained

[Clint1000]

thxs..