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Analog output behavior after the task has stopped

I have noticed that when I clear an Analog Output task ( on the 6723 ) that the channel maintains a DC signal.
 
This is actually the behavior I want, but I am concerned that this behavior may not be consistent across other NI analog devices.  I have read some NI documentation where other users have experienced the signal dropping to 0v when the Output task is stopped.
 
This is an issue because my software will be used to control multiple NI Analog devices ( 6723, 6040, 6115, and others) and I need to exercise some control over these Outputs to ensure they operate similarly.
 
Background:
I need to be able to support multiple DC outputs and at least one Waveform output at the same time.
 
I considered making these DC signals software timed tasks and the waveform signal a hardware timed task because most NI Analog hardware supports only one hardware time task and multiple software timed tasks.  This would give me control of all of the outputs since they would all have an associated task.  Unfortunately the 672x series devices do not support a single hardware task and multiple software tasks. (see knowledge base article)
 
Where I am now:
So now I am looking into using the DAQmxSetAOIdleOutputBehavior() to try and force the cards to maintain a DC level output when the task is cleared.  I have attempted to use this command on both the 6723 and the 6040 Analog devices unsuccessfully.  They both report that the property is not valid for that device or task type.
 
Is this expected?
 
Is there an easier why to do this?
 
To reiterate:  My current software works fine for the 6723,  but since I am not actively controlling the DC outputs ( I simply clear the task and the DC signal remains) I am concerned that other analog devices will not behave the same.  How can I controll this?
 
Thanks,
Anson Wooten
 
 
 
 
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Hello,

Yes, you are correct not all National Instruments Analog Output devices will continue to output the last updated value after cleared.  However, I can confirm that all E, B, S (61XX), M (62XX), and 67XX devices will continue to output the last updated value.  The channel property Idle Output Behavior for Analog Output is not a supported property for the devices you have listed.  I have seen this particular property used with a Modular Instrument (MI) - DSA device, which is one of the NI Analog Output devices that do not always continue to output the last value that was updated.

Samantha
National Instruments
Applications Engineer
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Samantha,
 
Thanks for your reply.
 
The product lines you've referenced are the only ones I expect to encounter, so I will allow my software to continue to operate as is.
 
One more quick question:
Are there any disadvantages to allowing these DC signals to remain after I clear the task??
 
Thanks,
Anson 
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A Wooten,

This question is very application specific.  Just be sure you are aware these DC values exist when making your Engineering decisions.  As long as your application functions as you expect it too, even after you clear the task, then I do not see a down side to allowing these DC signals to remain.  Have a great day and good luck with your application!

Ryan N
National Instruments
Application Engineer
ni.com/support
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