50103-related problem using DAQ Express Assistant Express VIs

[cbp952]

Hi,

I have an application where I am using 3 M-series modules in a CompactDAQ backplane to capture 5 different signals in a timed while loop. 

I have configured the DAQ Express Assistant Express VI to gather 3 analog input signals using virtual channels on an NI 9205 module (in slot 3 of the backplane).  If that's all I do in the loop, everything is wonderful and the application screams along.  I can take hundreds of samples per second.

I then add a 2nd DAQ Express Assistant Express VI pointing to either of the other two modules -- an NI 9219 module (in slot 2) where the Express VI is configured to measure a resistance value, or an NI 9401 module where the Express VI is configured to measure edge counts (that module is in slot 6 of the CompactDAQ backplane).

In either case I start getting 50103 errors.  So I did my homework and found a KnowledgeBase article that discusses what is happening ("Causes of NI-DAQmx Error 50103 "The Specified Resource is Reserved").  That was very helpful.  I tried connecting the Error Out of the first VI to the Error In of the 2nd VI and the error message went away.

However...  my application now runs *extremely* slowly.  Instead of being able to take hundreds of samples (loop executions) per second, I now can take only a sample every 2 - 3 seconds!

I thought the problem might have to do with the starting and stopping of the Express VIs - so I have been playing with connecting the Stop input to the boolean switch used to stop the loop as suggested in various template VIs.  This does not solve the problem though - actually, it causes the 50103 error to come back.  I really do think it has to do with the starting and stopping of the VIs though - or perhaps something subtle having to do with the modules being in a CompactDAQ backplane and USB communications.

So I am at an impasse.  If anyone has any insight into what is going on and what I should try next, I will be more than grateful.

Thanks in advance for your help.

[Dennis_Knutson]

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