Sample rate for output from a USB-6211 DAQ card?

[mchini]

Hello -

I am using a FireWire CMOS linescan camera to read an interference pattern, then using a simple Fourier transform spectral interferometery (FTSI) phase retrieval algorithm to detect the relative phase between successive shots.  My camera has a linescan rate of 28 kHz, and I have timed my phase retrieval algorithm to take ~0.7 ms (from camera trigger to phase output). I am using the phase signal to control a piezoelectric stack, by sending a single sample voltage to the analog output of a USB-6211 DAQ card.

Sending this voltage output increases the time of my loop to nearly 4 ms. I would really like to achieve a 1 kHz or better sample rate. Is the problem with my DAQ card or with my computer processor? Can any NI DAQ cards support such high speeds?

Thanks,

- Mike Chini

[Dennis_Knutson]

See this very recent thread about doing a single sample update.

[stilly32 · Accepted solution]

Hey Mike,

With USB, your loop rate is going to be around or under 1khz even on the best of systems. USB has higher latency and less determism than PCI and PCIe. You can get much better single sample AO rates on a PCI card, potentially a PCI-6221. We have some benchmarks for RT targets for AI/AO in a loop, you should be able to get similar performance in Windows, though if you're doing a lot of other processing your loop rates can suffer. 

Hope this helps, 

Andrew S

[mchini]

Thanks, I tried my application on a PCI DAQ card and the single sample acquisition time is about a factor of 10 smaller.  Thanks for your help!