Simultaneous analog and digital acquisition

[AutoMeasure]

Hi. I need to acquire 1 analog signal and 2 digital signals simultaneously at 300 kS/s per signal, with sampling triggered by another digital signal. I'm considering using NI's PCI-6122 simultaneous sampling daq card and acquiring the digital signals using analog channels. But do you know of any better/cheaper alternatives? Are there any products or configurations that can sample analog and digital channels simultaneously? I don't think a two-card approach would be cheaper, and there may be difficulties with programmatic synchronization of data.

Thanks very much.

[Ton Plomp]

First of all I don't knwo the 6122.

But for this kind of acquisition (1 analog and 2 digital) I'd use a 'normal' M-series daq card (6221 too slow, 6251 will do)

Set the clock timing source of the digital input (on port 0 for timed input) to 'Analog sample clock' rising edge.

For the analog input set the trigger start to a PFI-line which has the digital trigger.

Make sure you start all the tasks before the digital trigger arrives.

Now when the trigger arrives the sample clock of the Analog input will start, and thus will start the digital input!

Show your code!

Ton

[peteski]

First of all I don't knwo the 6122.

But for this kind of acquisition (1 analog and 2 digital) I'd use a 'normal' M-series daq card (6221 too slow, 6251 will do)

Set the clock timing source of the digital input (on port 0 for timed input) to 'Analog sample clock' rising edge.

For the analog input set the trigger start to a PFI-line which has the digital trigger.

Make sure you start all the tasks before the digital trigger arrives.

Now when the trigger arrives the sample clock of the Analog input will start, and thus will start the digital input!

Show your code!

Ton

I agree that the 6251 ought to do the job, although I would like to suggest some caution. Do you know what voltage levels you would be sampling on the analog channel? If they are in the same range as the digital signal, then taking the digital signals as analog inputs could be a good "quick and dirty" way to be sure of "synchronicity". If, on the other hand, you were reading very low voltages on the one analog signal and required a gain change between the channels, the 6251 would be multiplexing through a gain change which could contribute to error on the reading of the analog signal. If this were the case, the 6122 would have the advantage since each channel has its own gain and adc, not a multiplexer feeding one amplifier and ADC like the 6251.

If you want to go the more advanced route and separate the digital and analog channels, a way to be sure of sychronizing them would be to use one of the counter/timers to clock both the DI and the AI reads. That way you could prepare the AI and DI channels first, then setup the counter/timer channel to start triggering your AI and DI reads by triggering off of the external 300 KHz signal. If you do this, the 6251 would not have to multiplex its AI reads at all. Its more work, but you'll learn alot along the way!

Hope this helps!

-Pete Liiva