Can I graph an Analog Output channel?

[RSG]

I am working on a program to control an external device, using an Analog Output.  Because of various constraints, most of the time I don't have actual hardware to work with, but a simulated device works fine for development.  However, it would be nice to have some visual feedback of the output signal.  So, I'd like to plot the output of the AO task.

Obviously, one approach that would work if I had real hardware would be to externally wire the analog output to an input channel, but I can't do that with a simulated device.  Is there any way to do this?

It would also be useful when the hardware shows up, in that I wouldn't have to use an input to monitor the output's progress.

So, is it possible, or am I out of luck?

Thanks,
-Bob

[CharlieM]

Howdy Bob,

First, what device are you using? Second what kind of data are you writing to the device? For example, if you were using an NI M-Series card and writing and array of doubles, you could display this on the front panel with a waveform graph.

[RSG]

I'm using a PCI-6229, and I am writing doubles to one of the Analog Output channels.

But what I really want to do is display the data actually being sent out of the D/A itself.  Now, of course, if I had the actual hardware and a free A/D  channel, I could wire that, but what I really want is to do this with the simulated PCI-6229.  In many ways, that would be cool!

Thanks,
-Bob

[CharlieM]

Bob,

I’m not sure what data you want to see. The doubles you are writing can be displayed in the front panel as a single double, an array or in a graph. Those doubles get turned into binary by the driver and the binary is sent to the 6229 where the digital to analog conversion takes place in hardware.

I would suggest looking at examples for analog output in LabVIEW Help>>Find Examples. You can also set up a simulated 6229 in the Measurement and Automation Explorer. To set up a simulated 6229, search the Help of the Measurement and Automation Explorer for an article named “Creating NI-DAQmx Simulated Devices.” A simulated device can be used with LabVIEW.

[RSG]

What I want to see is the (simulated) analog voltage being created by the D/A.  I am writing a buffer of data at a time to the D/A, and I would like to see (near) real-time feedback of the analog voltage being generated.

If I was using real hardware, I would connect the D/A output to an A/D input, but I am not using real hardware (yet).

However, I am using a simulated 6229, created exactly as you mentioned.  I am using the simulated device in LabView, so I know that's possible - and a very cool feature that is!

Does the simulated device allow examining its (simulated) output?

Thanks,
-Bob

[CharlieM]

Bob,

I think I now know what you’re getting at. Unfortunately, there is no simulation that can show you how long it takes to get your data through the DAC (you could write your own). For a few examples: A USB 6229 could take as long as seconds when LabVIEW is running in a windows environment. A PXI or PCI 6229 in windows would be much faster because of the faster bus. However, you are still at the mercy of the nondeterministic operating system. At best, you could have a PXI or PCI 6229 running in a real-time OS environment.

In writing simulation code for such a task, which couldn’t ever be accurate, you would have to take into account all the process running on the computer, the type of computer, the bus (the only easy consideration) and finally the whims of the OS.

[Kevin_Price]

Bob,

Maybe you could submit a product suggestion? 

I agree that there's room to enhance our ability to query properties of a DAQmx output task buffer. 

-Kevin P.