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PCI-6132 Sampling Rate

Hi,
I'm using a PCI-6132 DAQ board to sample four analog channels.  I'm working in Labwindows/CVI V8.11.
I use a call to DAQmxCfgSampClkTiming(...) to configure buffered sampling at a rate in the range of 1.0 to 2.0 MHz.  Depending on what I specify for the Rate argument to the DAQmxCfgSampClkTiming(...) I do not necessarily get an actual sample frequency that matches
the Rate value.  For example if I program a rate of 1.3Mhz I get an actual rate of 1.3333MHz.
 
Here is what I assume is going on (please correct me if I'm wrong):
It is my understanding that the fastest internal clock on the PCI-6132 is 20MHz so the closest frequency that can be generated is 15 cycles of 20MHz which results in 1.33333MHz.
 
3 Questions:
1) What is the correct attribute to read to get the actual sample rate?
 
2) Is 20 MHz the fastest internal clock on the PCI-6132?

3) Where is this described in the documentation?
 
Regards,
Kirk
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Hi Kirkm,


Thank you for posting on the National Instruments forum.

 


To answer your first question, the correct attribute to read the actual sample rate is explained in the How Is the Actual Scan Rate Determined When I Specify the Scan Rate for My Data Acquisition?


The fastest internal clock on the PCI-6132 is 2.5 Mega Samples per Second.  You can find this in the Specifications Manual on page 2.  The specifications manual can be found  by clicking on the PCI-6132 product page, selecting the Specifications tab and then clicking on Detailed Specifications.

Thank You,

Nick F.
Applications Engineer
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 Nick,
 I apprciate the help. 

Just to clarify: To get the actual sample rate would I use a call something like this?
 
 DAQmxGetTimingAttribute (taskHandle, DAQmx_SampClk_Rate, &actualRate);

 On question 2).  Yes I understand the fastest sampling rate is 2.5MHz as stated in the spec manual.
 I was asking if there is a clock faster than 20Mhz that can be used as the clock that gets divided down to 2.5Mhz? (to get better rate resolution at the fast sample speeds)
 Thanks again,
 Kirk

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Hi Kirkm,

DAQmxGetTimingAttribute
is the correct function that you need to use.

There is also not a faster clock that you can use to divide down to a clock that's closer to 1.3 MHz.  You would have to either use 1.33333..  MHz, 1.25 MHz or wire in an external clock that is 1.3 MHz to a PFI line and use that external signal as your sample clock.  You would basically use the DAQmxCfgSampClkTiming and select the source as the PFI line that you are wiring the signal into.

If you have any more questions, please let me know.
Thank You,

Nick F.
Applications Engineer
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