PXI-6255 AI sample rate

[jharris66]

Hello,

We are using a simulated PXI-6255 device and with the LabVIEW example it appears we can achieve a sample rate of 20Khz for 50 channels without warnings or errors. 

From the spec it appears the max # of channels for 20Khz should be about 38 channels  (750000 / 20000).

1.25 MS/s single channel 750 kS/s multi-channel (aggregate)

Could the simulation not be representative of the specific device or does the real PXI-6255 support a higher rate than we expect?

[John_P1 · Accepted solution]

Hi jharris66,

There isn't a driver limitation to the sample rate, so a simulated device won't report any errors in this case.

In this particular example, I believe the 750 kHz limit comes from the settling time of the multiplexer.  I wouldn't expect to see any error messages even with the real device, but your accuracy will probably not be up to spec due to not allowing enough settling time between channels.

The 1.25 MHz limit comes from the max sample rate of the ADC.  You can probably exceed this number by a little bit, but once you go too far beyond 1.25 MHz you'll eventually receive a clocking error from the hardware when the ADC can't keep up.

So, the spec is still technically 750 kHz for multi-channel acquisitions.  You can probably run at a higher rate than this (even on real hardware) but I wouldn't say it's supported.

Best Regards,