Possible bug: DAQmx create channel w/o specified in task

The VI DAQmx 'DAQmx create channel (I-voltage-Basic) .vi' requires no task should be connected, and claims his detailed help "" task in specifies the task to add virtual channels, this VI creates. "." If you do not specify a task, NOR-DAQmx creates a task for you and adds the virtual channels that this VI creates to this task. »

My recent experience, I think that there is a problem with this feature. If no job is specified, sometimes this VI will create a new task without problems, but other times it will overwrite an existing task, causing errors later when you try to reference the crushed tasks.

In my code, I have 7 tasks, two digital (DIO), an analog to (HAVE) and four analog out (AO). One of the AO and the tasks of the AI does not use a task VI before the channel VI create. I recently added this AO task without creating a new task manually, based on the reproduction of legacy code for the channel of AI that also not create a new task. With two spots missing the task of creating VI, I found it fairly common (20% of the tracks) a further task would be crushed, causing errors when the task has been used, either be the wrong type IO, a wrong number of channels, etc. I think I saw this error until I added the second task without creating a task, but it's so rare that he didn't pay much mind, and I would just restart my VI. Now that was occurring more often, I've been tracking it. Simply by adding 'DAQmx create Task.vi' before calling Create Channel and the new task of wiring in the task, the problem seems fixed.

It is easy to add to create a task to avoid this problem, but it seems to me that the detailed help for Create Channel indicates that it is an unnecessary step. Thank you.

Hi MDI - AJT.

This looks like a problem with the code you posted, by suggestion of Norbert. When you create the task handles, you should do this only at the beginning of your code outside the loop, otherwise you will create errors that you overwrite memory locations at each iteration. If you move your virtual channel calls create outside of your loops, and does not call the handle of the task to be authorized beforehand (and implicitly create the task rather than explicitly), then this behavior must stop.

I recommend to try this with a single line, and not 7 DAQmx calls and follow the DAQmx architecture as seen in the examples under 'Help' "'find examples' and see if this behavior persists. Later architecture, I was not able to re-create this behavior.

BeenCoughin

Tags: NI Software

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