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AI Current DAQmx Create Virtual Channel Measurement Issue

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Hello, 

 

I'm relatively new to LabVIEW and have been experiencing an issue with getting all of the virtual analog input channels I have set up to output to my data file. For some reason, only some of the channels read out to the data file and their channel names do not stay with the measurements.

 

In the VI below titled "AI Current Test.vi", the data output file only shows three channels instead of the six shown in the VI and they are all unlabeled. In the VI below titled "Test VI 5.vi", the data output shows the four channels seen in the corresponding VI and they are all labeled with the DAQ module # and pin #. 

 

I'm stumped as to why I'm seeing this issue with "AI Current Test.vi" and would appreciate any help you could give me. I'm not getting any errors, but the output file is not generating correctly. This VI is messy because it is a component of a larger VI I'm using for a test in the near future. As I said, I am fairly new to LabVIEW so my work is clumsy. 

 

Thanks!

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Accepted by topic author zhale
05-15-2019 11:34 AM

Hello zhale,

 

It appears that your conversion between dynamic data and doubles are causing this information to be lost. Can you try to cut out this conversion step and just allow the coercion dots to be there similar to Test VI 5.vi?

Cullen C.
Technical Support Engineering
National Instruments
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Cullen, 

 

Thank you! I actually came to that same conclusion earlier today. I had converted from dynamic data to avoid the coercion dots because I worried about performance. It seems any effect these have isn't noticeable. Should I be worried about the coercion dots for any other reasons?

 

Best, 

 

Zach

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Hi Zach,

 

In this case, it shouldn't be a problem. In general, you should match data types as much as possible, but if LabVIEW is having to convert just a few extra numerics, that won't affect performance very much. If the coercion dot was on an array, this would be where you might have a problem.

 

This article describes the different effects of coercion dots, if you would like to learn more about this.

 

Best,

Cullen C.
Technical Support Engineering
National Instruments
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