Equivalent Input Referred Noise Of M Series USB-6251

[Padhu]

Hi All

I am currently working on a data acquisition system using the NI DAQ USB-6251. The application is to capture analog signals from specimens and carry on with furthur analysis. To proceed with the experiment, I need the Equivalent Input Referred Noise of the USB-6251 as well as the bandwidth concerned.

It would be really useful if you guys can help me out with this.

Message Edited by Padhu on 08-31-2009 09:51 PM

Message Edited by Padhu on 08-31-2009 09:52 PM

[piggieq]

Hi Padhu,

I believe you contacted us via email yesterday.

I'm posting below my answer to you in the email for benefiting the community.

The equivalent input-referred noise of our devices is not available in the specifications because it is specified in another form.

According to a few of the documents that we found online, it looks like input-referred noise refers to the how much the code-transition noise deviates from ideal.  It looks like they just take a low noise DC signal, such as ground, over several points and plot them on a histogram.  Then, they take the standard deviation to calculate the random noise apparent in the ADC. 

In our specifications, we specify the standard deviation of random noise on page 5 of the NI 625x Specifications (http://www.ni.com/pdf/manuals/371291h.pdf).  This is where I pointed you to yesterday, and it includs all the possible ranges in the AI Absolute Accuracy Table.  Again, this is the random noise spec for our entire front end and not just the ADC.

In regards to the bandwidth, the smallest signal bandwidth is specified at 1.7MHz for the analog input.

Best regards,

Guo Min

Applications Engineer

National Instruments ASEAN