6731

[dmourer]

Is there a way to configure the 6731 to to step through an array of voltages and output each index at a specified time interval?

[Christer]

Yes, this is what this board does and it should be a fairly straight forward excercise.

Configure the AO and load the array into buffer set the operation upto generate n number of times or continuous and start the generation. This is basically a simple point and click configuration using DAQmx. Even at the max sampling rate you shouldn't have any problems. If you are concerned about performance because you have many things going on at once try to keep your waveform under 8192 samples as the entire waveform will be loaded into the onboard buffer and you won't have system dependent latencies to deal with because of DMA data transfers. If your signal is repetitive in nature then only create an array with one period and then repeat it for however many times you want, the buffer will simply circle and you don't need to reload the waveform into the buffer.

The next thing to deal with is your definition of specified time interval.
Options:
1. If this means at a set rate then simple use the internal clock and tell it at which sample rate you want the generation to occur.
2. If you have an external clock you want to use you simply feed this into the right pin on the connector block and setup the waveform generation to use external clock instead on the internal one.

I think that should cover it

[chericks1]

Hi dmourer,

Absolutely! There's a great shipping example if you have LabVIEW that shows exactly how to do the above. The example is WRITE DIG CHAN - EXT CLK.vi, and it's meant for boards like the PCI-6731. I've included it as an attachment.

The example shows how to create and output a waveform with the appropriate time interval necessary for your application. It configures your digital output line(s), sets the external clock, and then outputs the voltages according to that clock. It's perfect!

Hope this helps!

Chad AE
NI

[dmourer]

Thanks for your help. I tried to open the example but I am missing a vi called create digital waveform.vi. I can't find it in the utilityllb.

Also, can I use DAQmx vi's for 6731? When I open MAX, the 6731 only appears under Traditional DAQ devices.

Thanks.

Dave

[Quantumbyte]

Hi,

The 6731 is supported under version 7.3 of DAQmx, earlier versions don't support the 673x devices.
On the other hand, the Digital waveform is only necessary if you want tou output timed digital data, not timed analog data, as you specified in your first message. If you use DAQmx (I strongly recommend it, it's much simpler and reliable) and LabView, you can take an existing example like: Gen Mult Volt Updates - Int Clk.vi, and then modify it to use Sample Clock instead of waveform as the sample timing type and writing your array of data instead of the waveform. Christer suggestion (keeping the number of samples below 8192) will only be effective if you also set the Use Only Onboard Memory property to true (Channel Property Node -> Analog Output -> General Properties -> Advanced -> Data Transfer and Memory -> Use Only Onboard Memory).

[dmourer]

How do I determine what version I am running?

[Christer]

Go to the Measurement and Automation Explorer (MAX). Click on the Software option (Expand the tree) and select NI-DAQmx and it will tell you the version in the attribute window. If you need to download a newer version of the DAQ driver go to Drivers and Updates on ni.com and download it (large download) http://digital.ni.com/softlib.nsf/MainPage?ReadForm&node=132010_US

-Christer

[dmourer]

Thanks for the advice. I now have NIDAQ 7.3 and am able to use the DAQmx functions, but I'm not sure how to configure the Gen Mult Volt Updates - Int Clk.vi to write the array of voltages.

[chericks1]

Hi dmourer,

I've included an example of how to build your own waveform. Remove the Waveform Buffer Generation VI, and construct your own waveform in its place. I've included an example of how to use the Build Waveform VI. Just respond if you have any further questions!

Chad AE
NI

[dmourer]

Thanks Chad, your example is exactly what I need.

I have one more question. I am scanning seven channels. Four are DC voltages, and the other three are outputs from current excited accelerometers. Can you tell me how to configure the channels for these types of measurements? Thanks.

Dave