MyRio samping-rate, ADC, loop time

[S1066]

I am stuck with a few concepts all intermingled in a mess, which usually means I have the wrong idea about one or all of those concepts. Posting here to see if anyone can point it out. I read quite a few related posts, but they didn't quite seem to address my queries.

From specifications, the aggregate sampling rate is 500 KHz. So if I use a single channel, I should get 500 Khz sampling rate. Therefore if I run a For-loop to acquire 500K samples of analogue data from AI0, it should take 1s.

      However when I tried to test it as in image attached , it took 3.67 seconds even though only one channel is used. Another VI in the same project uses a different channel, but it was neither connected nor running.

I do not understand this?

[S1066]

I really need to understand this for a project, so would appreciate any help even if I am overlooking something that should be obvious. I get easily confused where sampling-rates are involved.

Assuming my assumptions in the first post are correct, I have a few more questions.

What happens if I acquire data from two channels in the same For-Loop?

              Will it take double the time to complete? 4us instead of 2us (for 500k samples) at 250KHz. When I tried this, the time taken was 5.06 seconds which isn't quite double 3.67s.

What kind of sample-rates are achievable with FPGA?

         I read that FPGA can be faster, or is that also limited to 500KHz except for each channel and not as an aggregate? It wasn't quite clear from the User Guide and Specifications sheet. Is there another document I can refer to?

Thanks to anyone who might reply in advance!

[Bernadine]

Hi S1066

To achieve the desired effect, you need to

• Remove the For Loop
• Change the analogue input from "1 sample" to "N sample" - this will give you the option to state the number of samples (in your case 500000)

However you have chosen to use an express vi - this approach is less likely to achieve the desired speed. Please consider creating an FPGA vi as it is more likely to achieve the number of samples at the rate you require. 

Kind Regards,

Bernadine