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What you have been trying to do is the right way of logging data in DSC -- you browse your Server (DAQOPC in this case), generate Items and hence Tags. Log these Tags with appropriate deadbands.
You may want to get in touch with NI's Technical Support to resolve the DAQOPC problem.
You could theoretically use direct VIs and then write data to Memory Tags and log these, but this is not the right way of doing things, and will be very cumbersome.
Rgds,
Khalid
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