Aileen,
1. as this question doesn't seem to be related to motion control you should post it to the data acquisition or LabVIEW forum.
2. Your example uses the DAQ Assistant. With this approach the buffer size is selected automatically by the driver. If you need more control you should use a lower level approach like using the DAQmx vis directly. The buffer size can be changed with the buffer property node then.
Best regards,
Jochen Klier
National Instruments Germany
