Synchronize 9237 and 9401 in cDaq-9174

[Mrgoomis]

I previously posted this question in the labview sub-forum but at this point this seems a more appropriate place for it.

I am trying to get synchronized torque vs. angle plots using a 9237 for a torque/strain signal, a 9401 for a digital encoder signal, and a cDaq-9174 chassis to share clocks.

I have been working with NI support to get the clocks synchronize between the modules. I initially had the 9401 set up to generate a clock signal and the 9237 would read it internally for sampling. Unfortunately this method worked when using virtual equipment but the 9237 would not obtain samples with real hardware(Times out before any samples could be acquired) So now I am running the angular encoder off of the oversample clock generated by the 9237. This way seems to work correctly as far as data acquisition goes. Now I am back to the offset between the sources, I understand the 9237 will have some offset due to the oversample clock and acquisition/filter delays. The problem I am having now is that the offset does not seem to be constant. I am running a 1hz digital waveform (using an external function generator) into both the 9401 and 9237 using a voltage divider. I confirmed there is no lag between signals using an oscilloscope. When reading these inputs into my vi there is an offset but it is not constant, given the synchronize clocks I do not understand why this is happening. See attached picture

[aNIta B]

Hi,

      Is it safe to assume you've taken a look or are using this community example?  Additionally, Have you also taken a look at this KnowledgeBase article? Finally, since you posted this the Real-Time Measurement and Control forum- are you using cRIO or a Real-time opperating system?  If you're just using cDAQ, then I would recommend putting this in the Multifunction DAQ forum.  Otherwise, you may also want to post your code.  Thanks, and happy Thanksgiving!

[Mrgoomis]

That community example was just posted by the support engineer that I am currently working with.

I have looked at that knowledge base article but unfortunately the sampling delay offset is not consistent from one run to the next. The variation in the timing is shown on the scatter plot from my OP.

I am just using cDaq running labview on WinXP. I figured some of the people with real-time experience may have had better knowledge of referencing clocks and offsets and what not. I should probably re-post this in Multi-Function DAQ as you've suggested, there isn't a way to move a post is there? 

[aNIta B]

I'm still not sure what the best way is to correct the offset.  There's not a way to move a post, but I would recommend creating a new thread on the multifunction DAQ forum.  I'd recommend posting your code there as well, especially so everyone can check out the changes you've made since the community example was posted.  Thanks!