Generating 80 kHz sine wave output with USB-6453

[JayWW]

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@santo_13 wrote:

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@JayWW wrote:

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@Henrik_Volkers wrote:

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@santo_13 wrote:

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@JayWW wrote:

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@Henrik_Volkers wrote:

you can try a external low pass filter..

What THD you need?

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THD isn't super critical. That being said, I am trying to generate function generator caliber signals. What would implementing a low pass filter accomplish?

Thanks!

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very clean sine wave has very low THD, so, yes, THD is important

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I have to agree 100% to santo_13 ,  what do you mean with "generate function generator caliber signals"?  

calibration?  synchronisation?   

What do you want to do? 

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THD isn't hyper-critical for my application. I just need a decent sinusoidal waveform, at 80 kHz, and a specific amplitude, for two seconds on, and 8 seconds off. 

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In that case, then a 250ksps sample rate should give you a "decent" sinewave at 80kHz as it already satisfies the Nyquist criteria.

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Unfortunately, sampling at only double the desired frequency, or in this case, just over 3x, isn't enough to get a decent sine wave. Please see the attached image. I have other methods of generating the desired frequencies that don't involve using the USB-6453. I just figured, if I could do it all with one device, it would be a cleaner install.

[RIObotics]

Hi Jay,

Yup, that picture looks about right.  Outputting a 80khz signal with a max AO update rate of 250khz would give you about ... only 3 samples per period, hence your signal looks more like a triangle wave than a sine wave.  For a sine wave, you'll need at least 10-20 samples per period, to get a smooth signal.  Looks like you'll need a DAQ with faster AO update rate.

For what it's worth, we have secondhand USB-6361 units for sale at Extend Test: 

https://extendtest.co/products/usb-6361-16-ai-16-bit-2-ms-s-2-ao-2-86-ms-s-24-dio-usb-multifunction-...

This unit has max 2.86 MS/s update rate for analog output, which should be sufficient for your 80kHz output.  Maybe you can move your analog input tasks to this device as well, and keep AI and AO all within the same device.

BR

John

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