Run DAQ at multiple timings?

[xkenneth]

All,

I posted this in the LV forum first, but didn't realize that the multifunction DAQ forum existed. I have a cDAQ-9172 loaded with 4 NI 9239 modules. I'm content sampling all of the channels these modules provide at about ~500 S/s however I have one channel that I need to sample at about ~15000 S/s. Is it possible to have this DAQ module sample at various speeds? The obvious thing to do is bump all the channels up to 15k S/s and downsample, however this can be quite a processing load. Any suggestions?

Regards,

Ken 

[Dan_K]

Hello Ken,

This is not possible using CompactDAQ.  The cDAQ-9172 only has one analog input timing engine.  As a result, only one analog input task can run at a time, and only one sample rate can be configured for a task.  If having multiple continuous input sample rates is required for your application, the best way to get around this problem is to configure your task to run at the fastest required sample rate. You can then either resample or average the inputs of the other modules in software to simulate slower sampling rates. 

Some modules have a maximum sampling rate that may be well below that of the other modules in the chassis.  Using these modules will not constrain the ability of the faster modules to sample quickly.  Instead, if a sample rate is chosen for the task that is above the maximum rate of a slower module, this rate will be used and the slower module will simply return repeat samples.  For example, if your task is running at 1k Hz and the chassis contains a module with a maximum rate of 10 Hz, all modules will return 1000 samples a second, but the slow module will return 10 sets of 100 identical points.  For more information about sampling with the cDAQ-9172, refer to the NI cDAQ-9172 User Guide and Specifications.