AI Timing Issue

[MogaRaghu]

The hardware used is a USB 6221 which has a sampling rate of 250ks/s.

I am trying to acquire 1000 samples of one single channel inside of a 50ms Timed Loop . Thus the acquiistion must be over in 4ms maximum as each sampling time is only 4microsec.

But when I run the Chart_SinglePlot.vi the Finished Late LED is always as the 50ms Timed loop takes something like 70ms for each iteration. ( The PC is a P4 / 2GHz / 1 GB ram with WIN_XP ) The VI is attached herewith.

Can anyone tell me whats going on ?

Thanks

Raghunathan.

[JB]

Hi Raghunathan,

For comparison : independently of the state of Plot, Iteration Duration is about 11ms on my machine running LV8.5 and with a PCI-6229.

WXP SP2 / P4 / 2.8GHz / 1G RAM


Message Edité par JB le 02-22-2008 05:09 PM

[JB]

There is just a question that went to my mind. Where do you configure the sampling rate ? You use a physical channel and therefore, unless I'm missing something, the DAQ interface will use its default sampling rate which is probably lower than 250kS/s.

[jiangliang]

Hi:
You should try to use Timed Loop in your case, and by setting the factors of time out, you might achrive your goal.

Anyway, there would be some improvement, but not sure if that can fit your requirement.

[MogaRaghu]

Hi JB,

You were right.

Once I took control over the sampling rate, the results were predictable.

I am herewith attaching the modfied VI and you can check it out.

Thanks

Raghunathan