Multi sample rate synchronization of 9234

[Lahan97]

Hello folks,

I am trying to start acquiring two NI 9234 module, 1 channel each, in a USB cDAQ 9174 chassis at the same time.  The two channels will be acquiring the same signal at different rates, one at the maximum 51.2KS/s the other at 2.56KS/s each channel/module will read 100ms worth of sample per iteration (5120 samples and 256 respectively) continuously.  Is this possible?

So far I have not managed to get the two sample in to be in phased.  I've only seen documents about syncrhonizing two modules with the same rate (being in the same task) and I can do that but  I haven't found anything about multi rate.

Thanks in advance.

[MegaWatts]

There is a community example that I think will help to illustrate what you are trying to do. I'll include a link to that here.

https://decibel.ni.com/content/docs/DOC-32105

May I ask why you need to sample the channels at different rates? If you could sample them at the same rate, you could use channel expansion which would require less coding.

[Lahan97]

Hi thanks for replying. 

I modified that example and synchronization is only true if they were both sampling at the same rate otherwise there would be roughly 2 ms of delay between the two waveforms or depending on how much of difference between the two sampling rate.  I have checked the timing properties of both tasks in both scenarios and they do indeed share one common timebase. 

So is there something else I am missing?

I am playing around with two different rates to see if I can avoid using filters.

[MegaWatts]

How are you creating the signal that is being measured in your code? How are you connecting it to your device?

[Lahan97]

Signal is a real constant analog 60hz signal coming from a function generator that was t'ed straight into ch0 of both module.

[Pittmanm83]

Hi, is there a reason I can't access this link? I'm doing something simmilar and want to exaust all options before posting specifically.

Thanks,

Matt P.

[Wild_man]

Matt, It appears that content was removed at some point. I found this community example that appears to be similar based on the title of the original page.

Multi-Device Synchronization of Analog Input and Ouput Using Multiple Rates and Trigger Skew Correction with DAQmx

https://decibel.ni.com/content/docs/DOC-11433

Thanks,

[trickey]

Great, thanks Alex!