How do I read back the output from an analog output channel as an analog input?

[MikeEbb]

I am writing a waveform to a DaqMX output channel. Does anyone know if there is a way to read-back what I am writing to an input channel in LabVIEW?

What I want to do is equivelent to physically wiring an input channel to the output channel.

Thanks,

Mike

[jpaul]

Hi Mike,

There is no way for you to internally route an analog output to an analog input. The only solution is to physically connect the two lines together with a wire.

I came to this conclusion through the following steps:

1- Start MAX and select the DAQmx device under "Devices and Interfaces>>NI-DAQmx Devices" that you want to internally route signals through.

2- Click on the "Device Routes" tab on the bottom of the right hand window (It defaults to the "Attributes" tab)

3- Line up the Source with the Destination to see if the connection can be internally routed (either direct or indirect)

I came to the above conclusion by following these steps for a PCI-6251 DAQ device (the analog output & input do not exist in the "Device Routes" tab therefore they do not support internal routing), but you should verify this for your specific hardware. Let me know if you have any other questions/concerns.

Cheers,

Jonah Paul
Applications Engineer
National Instruments

[MissyS]

Hi Mike,

Jonah is correct, you cannot internally route a analog output to an analog input. However, there is a different method we can use to read this voltage internally without jumpering the two terminals together, by exposing the internal terminals on the DAQmx Physical Channel control or constant. To do this, right click on your DAQmx Physical Channel control or constant, and select I/O Name Filtering.... Here, select the Internal Terminals checkbox and click OK. You should now be able to see the _ao0_vs_aognd terminal, which will give you the measurement of analog output 0 versus analog output ground. You should be able to have the _ao0_vs_aognd terminal in the same task as other analog inputs from the same board.

I hope this helps!

Regards,

[Jeff_Long]

Hi,

I'm also trying to read back the value of an analog output channel.  I'm using DAQmx 8.6.0f5.  I don't see anything about "Internal Terminals" when I select I/O Name Filtering from my DAQmx channel constant. 

Was this feature recently dropped from DAQmx?  Are there some situations under which these are not shown?  Are they shown even when only a simulated device (no actual device) is present in MAX?  I'm using a simulated PCI-6221 to develop a customer application offline.

Jeff.

[MissyS]

Hi Jeff,

I simulated a PCI-6251 with DAQmx 8.6, and was able to see its internal channels in the drop-down channel list. However, these will be analog input channels, not analog output. These internal channels allow reading from internal terminals, but do not allow control of intermediate voltages directly. To read back the internal analog output voltages, such as_ao0_vs_aognd, use an analog input channel control and specify to allow internal names.

I hope this helps!

Regards,