200040 AO Error on CompactDAQ changing with AI channel configuration?

[J Bowen]

I've got a test setup to experimentally show the AI.Convert property (or the time between channel measurements) for the NI 9205 module in a cDAQ chassi.  For my first setup I used one 9205 (for the Analog In task) and one one 9263 module (for Analog Output task).  In this configuration I was able to accomplish the following

 - Setup AI task with 16 diff channels (9205) reading continuously at 5KHz, AIConv.Rate @ 250K (4e-6 sec between channels)

 - Setup AO task with 1 output channel outputting @ 300KHz update rate, a 100Hz sine wave (generated 9K samples @ 300KHz)

 - Wired the single AO channel to the first and last differential channel and observe the induced phase shift (from the 4e-6 sec delay between channel measurements)

I tried a second scenario by adding in a second 9205 module (to test the syncronization between the starting point for each module) and:

 - changed the AI task to be 32 diff channels and setting the AIConv.Rate for each module to 250K

 - Kept AO parameters the same

 - Wired single AO channel to the first and last differential channe for EACH module

When I run the second scenario I get the 200040 warning/error on the AO task (during the Analog Wfm Write VI), which states "Measurements: Sample clock rate specified is so high that it violates the settling time requirements for the generation".

My question is why, when I change only the AI task, does the performance of the AO task get affected.  I was under the impression that the two were somewhat independent.  Especially when the error refers to the required settling time for the generation.  I haven't added in channels on the AO side.

Any ideas?  Thanks in advance

[Brad_K]

Hi J Bowen,

I consistently get the 200040 warning when I set the sample rate above 100 kS/s (using the device test panel in MAX). If you have two separate VIs for the two configurations (1x 9205 vs. 2x 9205), you might want to check whether you are using General Error Handler.vi. If "OK message + warnings" or "continue/stop + warnings" is not wired to the "type of dialog" input, General Error Handler.vi will not report warnings. If you are running the same VI for both configurations, posting a code snippet that demonstrates the problem would help show what's going on.

DAQmx always generates a warning above 100 kS/s for the NI 9263, although there are settling times besides 10 μs listed in the NI 9263 Specifications. Whether the NI 9263 outputs actually settle or not depends not just on the sample clock rate but also on how rapidly your waveform changes. At the high sample clock rate that you are using, a large voltage step (as opposed to the small steps in your sine waveform) would not settle completely by the next sample clock.

Errors in DAQmx have negative codes and warnings have positive codes, so 200040 is a warning. After a warning, DAQmx continues to run the task. An error would stop the task. For example, if you add more AO channels to the task or you set the sample rate too high, you will get a -200018 error, "DAC conversion attempted before data to be converted was available." This would indicate that a sample clock was generated while the previous sample was still being sent to the DACs.

A note about the AI.Convert property: if you use a version of DAQmx Read that returns a waveform (as opposed to an array), DAQmx uses the AI convert clock rate to adjust the waveform timestamps. This allows the LabVIEW graph indicator to display the waveforms more accurately in relation to each other, which in this case would make them line up instead of displaying phase shift. (Changing the plot style of the graph to highlight individual points would show more clearly what's going on.)

Brad