Difference of USB 6251 and PCI 6251 on analog input.

[John_P1]

What happens if you take out the FFT and Intensity plot?  Can the DAQ card keep up with no additional processing going on in that thread?

If removing the FFT and Intensity plot helps, you might consider trying a producer/consumer architecture to move the fft and drawing of the graph into a parallel thread.

Are you still getting buffer overflows?  What is the exact error code of this message (on-board FIFO vs. DAQmx Buffer in PC Memory?).

Best Regards,

[ustcmiaor]

Hi, John,

Thank you for your advices.

Firstly, the DAQ card still cannot keep up even without additional processing going on.

As to the error, it is onboard FIFO memory overflow. It is strange that this error happen irregularly, I mean, sometimes it happen after several seconds, sometimes several minutes.

Best.

[JÞB]

Ahh..

---

@ustcmiaor wrote:

Hi, John,

Thank you for your advices.

Firstly, the DAQ card still cannot keep up even without additional processing going on.

As to the error, it is onboard FIFO memory overflow. It is strange that this error happen irregularly, I mean, sometimes it happen after several seconds, sometimes several minutes.

Best.

---

I just read through this thread and think I may have an hypothisis to test:

Noted: USB on Laptop has lower than expected throughput- intermittantly.

The USB-6251 (as seen in pg 3-7 of the users manual) requires an AC adaptor to provide its power and an external GROUND wire to earth.  The USB cable will also connect the Laptop to the devices chassis ground, this USB wire should not be carrying current.  So, you also need to Ground the Laptop to the same point.

Without these external ground wires the current on the USB cable may introduce noise on the USB data signals requiring packets of data to be resent when bits get corrupted resulting in the symptoms you see.

[ustcmiaor]

Hi Jeff,

Thank you for your advice, I checked my system today, since both the three pin cable plug are connected to a same wiring board, can I say their ground are together?

Best.

Miao

[JÞB]

---

, since both the three pin cable plug are connected to a same wiring board, can I say their ground are together?

---

Not with any certainty.  Also, is there any conditioning on the primary power?-  Thinking forward- you experience this with USB but not PCI.  Makes me suspect a noisy building ground if adding the recomended external ground wire does not resolve the problem.