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Buffer Size Property Returns a Value Less Than Number of Samples to Acquire

Primary Software: Driver Software>>NI-DAQmx
Primary Software Version: 7.4
Primary Software Fixed Version: N/A
Secondary Software: N/A
Hardware: Digital I/O (DIO)>>High-Speed>>PCI-6534, Digital I/O (DIO)>>High-Speed>>PXI-6534

Problem: When performing a finite acquisition, why is the value returned by the NI-DAQmx buffer size property not the same as the number of samples to acquire?

Solution: When using a DAQ device with a large amount of onboard memory, such as the NI 6534 with 32 MB of onboard memory, we can consider two cases:

• You could have a finite acquisition that collects less data than the onboard memory. In this case, the data will be stored on the board and the buffer in your PC will be limited to 1,000,000 samples.


• If the total number of samples you are acquiring is greater than the onboard memory, then a PC buffer will be allocated that can hold all of the data. The buffer size property will return a value equal to the number of samples per channel you are acquiring.

You can check how much onboard memory is allocated per channel with the onboard buffer size property. This will be the total onboard buffer size divided by the number of channels you are acquiring from.

Related Links:
KnowledgeBase 31T899KD: How is the DAQmx Buffer Size Allocated for a Finite or Continuous Acquisition?
KnowledgeBase 2X87BR7Y: Where to Find NI-DAQmx Property Nodes Listings and Help

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Report Date: 08/15/2005
Last Updated: 09/07/2005
Document ID: 3OEE9N88

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