[fpga] Analog input configuration in NI 7965R

[WarWolf]

Hi all,

I have a NI FlexRIO (PXIe-7965R) FPGA card with an adapter module (NI 5733). I am using Labview real time 2012. My measurements are dominated with 60 Hz harmonic noise, which is very much likely due to ground loop. I am trying set my analog input channels in differnetial mode (as opposed to RSE, NRSE) in an attempt to overcome ground loop. I came across this link which explains how to configure  FPGA input channels -

http://digital.ni.com/public.nsf/allkb/08EF26D2E9041BC6862570E0001E442E

However, on opening the RIO device setup for my target, I found that there is no option to choose the channel configuration (as seen in the attached image). Does this mean that the analog channels are in differential mode by default? If not, how do I change it?

Any help will be greatly appreciated.

[BauerPower · Accepted solution]

Hi!

That KB is in reference to R series devices, not the FlexRIO product line. I know it's a bit confusing as the 7965 has an "R" designator at the end of the model name, however the R simply notes that it's a product with a user-programmable FPGA. 

Unfortunately the 573x FlexRIO adapter modules are all single ended so we won't be able to change them to differential. What is the frequency of the signal that you are trying to measure? Another option would be to set the 5733 to AC-coupled mode which would yield the following frequency response, greatly suppressing any noise below 10 kHz.

[WarWolf]

Rob,

The frequency content of the signal I am measuring depends on the instrument I have it connected to. sometimes the bandwidth of interest is 0-5kHz, and sometimes it is ~300 kHz. So I cannot use the AC coupling. I'll try to add some filter in my FPGA program to remove the 60 Hz harmonics. Thanks for you quick response.