Arbitrary Waveform Generation on a Multifunction DAQ

[Patty]

What are the limitations of producing arbitrary waveforms on a multifunctional DAQ such as the PCI-6071E?  Is it possible for the DAQ to function as an arbitrary generator?  The update rate on the DAC's of the PCI-6071E is quoted to be 1MS/s.  Does this not mean that I can produce arbitrary waveforms up to 500kHz?  Can someone help shed some light on the feasability of using the analog outputs of my multifunction to produce arbitrary waveforms.  Thank you.  Patty. 

[devchander]

Yes it is possible to use that particular DAQ card for Arbitrary Waveform Generation.

Go to LabVIEW examples and search for it.( you can draw a waveform on a graph and generate it on AO of the DAQ card)

I vaguely remember that this VI uses Traditional DAQ drivers.

So take care of that( install Traditional DAQ support for 6071)

and here is a brief note on the funda for slection of AO parameters for generation

To control the frequency, all you have to do is toy around with the update rate, cycles per buffer  and the buffer length

For ex

in case of sinusoidal wave generation,  if cycles per buffer = 10 and buffer length = 1000, effectively, each sinusoidal oscillation in the generated waveform will be represented by 100 points.

Now  if update rate = 1000, then you will get a sine wave of frequency 10 hz on the selected AO channel.

in the same case, if you bring the update rate to 100, frequency of sine wave generated on Analog output becomes 1 Hz.

for going to higher sampling rates, take a larger buffer size, suitable update rate and increase number of cycles

Just keep in mind, lesser number of samples per cycle, poorer will the quality of your generated sine wave be.

so represent each sinusoidal cycle by suitable number of points.(practically i have observed that each sine wave represented by more that 20 points looks decent. but the fact is that more number of points, the better sine wave you get )

hope you get the idea.

so a buffer size of 10000, cycles per buffer 100 and update rate 10000 give a sine signal of frequency 100 hz.

check out the maximum update rate and permitted buffer size that the AO of your DAQ card supports to calculate the max frequency you can generate using this VI

[Laura F.]

Hi Patty,

I'd recommend using NI-DAQmx as long as you have LabVIEW 7.0 or later.  If you are using a text-based language, I'd also recommend using NI-DAQmx.  It is more robust and easier to use than Traditional NI-DAQ (Legacy). 

To see an example of generating a waveform using NI-DAQmx in LabVIEW, open the Example Finder by going to Help >> Find Examples and then browse to Hardware Input and Output >> NI-DAQmx >> Analog Generation >> Voltage.  A good example to start with is "Cont Gen Voltage Wfm-Int Clk".  This will continuously output a waveform of your choosing. 

If you are using a text-based language, refer to Programming NI-DAQ in Text-Based Languages to read about your particular language and to find out where the shipping examples install. 

Let us know if you have additional questions.

Regards,

Laura

[devchander]

Even i would recommend DAQmx over Traditional DAQ anytime.

But I once again suggest you to look at the example I have pointed to.

The reason, the logic/code for arbitrary Waveform generation is well illustrated in that example.

Of course, you can implement this logic with DAqmx AO functions too

But, to get to know that arbitrary Waveform generation is indeed possible as required by you, that particular program is a confidence booster. that's all 

all the best

Message Edited by devchander on 07-07-2006 01:02 AM

[Patty]

Hi guys,

Thanks for the answers; not quite as clear cut as I would of hoped but I'll reserve my judgment until I can view this example VI (

Cont Gen Voltage Wfm-Int Clk).  Thing is it's not to be found in my LabVIEW 7.1 or 8.0 Examples folder.  Could someone please attach it.

Thank you very much,

Patty.

[devchander]

It should be there in examples.

have you installed NIDAQ device drivers along with labVIEW??