USB 6251 for waveform generator

[bkiley]

Hi All,

I'm doing some preliminary groundwork for a project for my company. I'm looking to get a USB DAQ device that can generate sine and square waveforms up to 300kHz, with an accuracy of +/- 5Hz, and be able to change frequency up to 5 times per second. Also, I will need to be able to count frequencies up to 300kHz, sine or square waveforms, and be within +/- 5Hz. Can anyone comment on whether the USB-6251 can do this and point me to some code examples to help speed my learning process.

I'll be using this with LabView Full Development system.

I would like to keep it USB if possible.

Thanks

[JÞB]

The Specs  Say you should be able to generate the Square wave easy but the 2.8MHz update rate (1 CH) is a bit lower than the 10 samples per period I like as a minimum for sine waves.  As a counter its onboard clocks spec at 50ppm so that gives you 2Khz accuracy at 80MHz onboard clock and 400Hz with the 20MHz clock (no need to discuss the 0.1Mhz) So your busted there without an external clock but the 32 bit resolution should give you sub mHz resolution at 300KHz

The rough part is how well your system can deal with the AO update latency. updating the AO 5 times per second is a pretty rough USB throughput if you do the periodic regen from the FIFO and worse if its from the host buffer.  The BIG question is more of a how fast do you need to switch frequency than a how often one.

I think you may want to look for an AWG as a source (with an available stable referance for your counter application) 

Message Edited by Jeff Bohrer on 01-26-2010 02:59 PM

[bkiley]

Hi Jeff,

Thanks for the reply. I have not yet used NI hardware/software for analog output, so please bear with me. By "regen the FIFO" I assume you mean that I will need to keep the AO buffer filled with the correct values for the given sample rate, and there will be a slight lag before the new data is being sent through the DAC?

While I don't need a DAQ that can do AWG, it would be nice if I could find one that can do simple waveform and only require frequency and amplitude information, instead of a constant stream of data, and still operate on USB. I think I'll look at some more of the USB devices and see if something has that capability.

Any suggestions for a USB AWG that works well with LabView?

Thanks for your help

Brian

[bkiley]

OK, I re-evaluated our needs and I will not need to generate the signals when testing at our customers site, only frequency counting and some digital IO. So I think the USB 6251 will work well for our portable setup.

So I should be able to find a seperate signal generator that can be controlled by USB.

Thanks

Brian