The buffer size set with AI Config is NI-DAQ's internal software acquisition buffer, and it is not related to the device's FIFO. The internal software buffer is a "circular" buffer in the sense that in a continuous acquisition, the acquired data will be written to the buffer until it is full, then the data wraps around to overwrite the data at the beginning of the buffer. When selecting the buffer size, you need to select a size that is large enough such that you can read data out of the buffer before it is overwritten. You will get a -10846 error if data gets overwritten. If your computer is not fast enough to read data from the buffer as fast as it is being acquired, then you will eventually get an overwrite error. But a larger buffer can buy you more time, and keep you from overwriting data in case your CPU is periodically busy with other tasks.
I recommend that you experiment with different buffer sizes to see what works for you. A good starting point might be 50000 scans (10x your sample rate). The downside to selecting too large of a buffer is that the memory will be page-locked, so it cannot be swapped out for use by other applications.
Joe
