Anti-aliasing in DAQ Assistant Express VI

[MinHolly]

Hello,

I'm using the DAQ Assistant Express VI to acquire a signal from a NI DAQ I/O module that has a sampling rate of 2 MHz. However, the DAQ Assistant Express VI allows me to specify a new sampling rate, which means that I can adjust the acquisition rate. My question is: Does this VI include an anti-aliasing filter?

For instance, if I'm acquiring a signal at 2 MHz(in the NI DAQ I/O module)  but I set the sampling rate to 100 kHz in the DAQ Assistant Express VI, does the VI include an anti-aliasing filter to eliminate frequencies above the new sampling rate?

I couldn't find any information about this in the VI's help section.

Thank you in advance!

[mcduff]

Most likely there is no anti-aliasing filter.

I do not know what kind of DAQ that you have so I am guessing that it is a SAR(Successive-Approximation-Register) device due to its sample rate. These types of DAQs have no AA filter. (Is your DAQ 16 bit, then it is a SAR)

DSA(Delta-Sigma ADC) DAQs have a built in digital AA filter; most of those only sample up to a few hundred kHz. (Is your DAQ 24 bit, then it is a DSA)

[MinHolly]

Thank you for your response.

I'm using a PXIe-6368 DAQ, and indeed, there is no anti-aliasing filter in it. However, the concern I raised is not about aliasing from the initial sampling done in the module, but rather the resampling in LabVIEW through the DAQ Assistant VI.

Do you have any idea regarding that?

[santo_13]

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@MinHolly wrote:

Thank you for your response.

I'm using a PXIe-6368 DAQ, and indeed, there is no anti-aliasing filter in it. However, the concern I raised is not about aliasing from the initial sampling done in the module, but rather the resampling in LabVIEW through the DAQ Assistant VI.

Do you have any idea regarding that?

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Whatever sampling rate you configure in DAQ Assistant is configured in the hardware (coerced to supported value); there is no software resampling.

[rolfk]

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@santo_13 wrote:

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@MinHolly wrote:

Thank you for your response.

I'm using a PXIe-6368 DAQ, and indeed, there is no anti-aliasing filter in it. However, the concern I raised is not about aliasing from the initial sampling done in the module, but rather the resampling in LabVIEW through the DAQ Assistant VI.

Do you have any idea regarding that?

---

Whatever sampling rate you configure in DAQ Assistant is configured in the hardware (coerced to supported value); there is no software resampling.

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That is correct. However if you acquire more than a ms or so of data, you have significantly more sample points than screen pixels.

Rather than trying to draw 100000 or more points in a space of 1000 pixels or less and creating one massive ink stain on screen, the data will be decimated to not draw more than one dot per screen pixel. This is purely a feature of the graph itself and has nothing to do with the DAQ device, NI DAQmx, nor the DAQ assistant. The data is still there as can be seen when zooming into the graph.

But aside from the fact that an ink stain on screen does little to let you see anything of the actual data, drawing a line or point on screen is a relatively time consuming task. Doing that 100000 times each update on a screen area that has only 1000 or 2000 pixels across is simply wasting lots of CPU time and energy!