Selecting sample clock frequency for NI 4472

[MiamiVipul]

HelIo:

I have been using NI 4472 DSA on a PCI slot for reading accelerations. I was reading the NI 4472 User Manual and under "Selecting your sample clock frequency", it specify two increments (95.37 uS/s for Fs<51.2 kS/s and 190.7 uS/s for Fs>51.2 kS/s). Can you explain what these increments mean? I understand the sampling frequency, but what does this time increment mean?

Also, it says "If you do not specify a rate at a multiple of the increment, NI-DAQ will automatically choose the next higher step for you". Dose that mean I cannot specify any random value for Fs? Dose it have to be a certain multiplication. Please explain this for a novice to Labview/DAQ.

Thanks a lot in advance.

[Jarrod_B.]

Hello MiamiVipul,

Those statements in the User Manual mean that the PCI-4472 only has a finite set of sample rates that it can produce.  The allowable sample rates are given by 51.2 kS/s - k * 95.37 uS/s or 51.2 kS/s + k * 190.7 uS/s, where k is an integer.  As you can see, the step size is quite small, so you still have a lot of flexibility. 

As an example, if you specify a sample rate of exactly 51.2 kS/s, that would be fine.  However, if you try to set the sample rate to something between 51,200 S/s and 51,199.990463 S/s (51.2 kS/s - 95.37 uS/s), the driver will automatically coerce that sample rate to next highest allowable rate, or 51.2 kS/s.  In order to find out the exact value that the driver is using, you can read the from the DAQmx Timing Property "Sample Clock:Rate" as shown below:



I hope this helps!

Best regards,

Message Edited by Jarrod B. on 01-04-2007 09:03 AM