MultiChannel Acquisition -- Simultaneous Acquisition of 1 MultiSample & 2 Single Sample Channels in a Task

[WBFTM]

I am able to get simultaneous multichannel sampling on my DAQ (USB-6363) without a problem. But what I want to do is get multichannel acquisition in a single task where the sampling requirements are different for each channel. For instance, I want I want to acquire a total of 1000 samples across 3 channels in a single task, with DAQmx read sampling characteristics as follows:

• ai0: Analog Wfm 1Chan NSamp (998 Samples)
• ai1 + ai2: Analog 1D DBL NChan 1Samp (1 + 1 Sample/Channel)

I know I could just do a regular multichannel multisample acquisition across all three channels and then average down channels 1 + 2, but I don't have that many samples to spare. ai0 is a bandwidth hog in my application and consumes all the samples from the DAQ (2 MS/s), but I can spare a few samples to make additional analog measurements (e.g.., temp, pressure).

Ai0 is also running continuously so the additional analog measurements on ai1 + ai2 need to be contained in the same task.

I'm not sure how to go about this or if it is even possible. Any ideas or thoughts would be greatly appreciated.

Currently I'm using a second DAQ to read these additional channels at a lower rate but I need to move everything over onto a single DAQ. 

[John_P1 · Accepted solution]

How continuous does ai0 have to really be?  You of course cannot sample on ai0 and either of the other inputs at the exact same time, so there would be some gap in your data.  Also, if you want to go at the full 2 MHz, you might need to sample ai1/ai2 twice in order to allow for the input to settle (the maximum specified multi-channel rate is only 1 MHz due to settling constraints on the MUX I believe).

DAQmx does sort of let you configure something like this if you "trick" it by configuring each sample as an individual channel in your task (see a similar example here).  So your 998+1+1 (or 996+2+2) becomes a 1000 channel task (takes up a bit more memory, but should still be workable).

I would consider a 2nd DAQ card a preferable solution if ai0 really does need to be continuous.  You could go with a cDAQ chassis (9174 or 9178) plus a 9223 (only 1 MHz though) for the fast input and your choice of module for the slower inputs.  On the cDAQ chassis a module may run a separate AI task from other modules (up to 3 AI tasks per chassis) at different rates.

Best Regards,