Multifunction DAQ

cancel
Showing results for 
Search instead for 
Did you mean: 

Different Sampling rates on USB-6218

Hi,
 
I understood that the USB-6218 has two seperate AI ports and therefore I can have a different sampling rate on each port? Is this correct?
 
If yes, how can I use this in the DAQ Assistant?
 
Cheers,
Dan
0 Kudos
Message 1 of 8
(3,567 Views)
Hi,

The USB-6218 has direct screw terminal connectivity. Each connectors provides access to AI, AO, DI and DO channels but: The USB-6218 has only one A/D converter, so every available AI channel is multiplexed to the same ADC and you've the option to set only one sampling rate for all AI channels, although it can be that the AI channels are on different screw connectors.

Hope that helps.

Luca
Regards,
Luca
0 Kudos
Message 2 of 8
(3,564 Views)
Thanks Luca,
That helps. But doesn't help my current project!! Can you tell me if the USB-6251 has more than A/D converter?
 
Cheers,
Dan
0 Kudos
Message 3 of 8
(3,560 Views)
No, it doesn't. Maybe if you explained what your project is exactly, and why you can't use a single A/D converter clock. There are things you can do to make it seem one channel is acquired at a different rate. Simply discarding extra samples in one channel is one option.
0 Kudos
Message 4 of 8
(3,555 Views)

I have 6 Channels that I need to sample at 10kHz and 8 Channels that only need samping at 1Hz.

If I sample all 14 channels at high speed I think i am going to running out of speed on the system. So would like to keep the high speed channels to a minimum.

I have read other posts about using decimation to throw away unwanted samples, but I assume this still gives the overhead in the hardware?

Thanks.

Daniel

0 Kudos
Message 5 of 8
(3,551 Views)
You should have no problem maintaining a 10 Khz sample rate on 14 channels with either the 6218 or the 6251. Especially with the 6251, that's well within the specs. Your effective sample rate per channel is the sample rate divided by the number of channels.
0 Kudos
Message 6 of 8
(3,548 Views)

OK, I see your point. think I had miscalculated that one somewhere.

What is the best way for me to discard the extra data for the 1Hz channels?

I am using the DAQ assistant. So should I just put the 1Hz analysis code inside a 1Hz timed loop?

Or is there a better way to sort the Dynamic data output?

Thanks again.

Daniel

0 Kudos
Message 7 of 8
(3,541 Views)
I don't use the DAQ Assistant or dynamic data but with waveform data types, I'll usually just take the mean of the oversampled signal.
0 Kudos
Message 8 of 8
(3,536 Views)