I am getting noise clusters in differential mode for ground refeenced source

[Salman Anwar]

I am using DAQ board PCI-MIO-16E-1 and 2090 BNC as termination accessory. I want to aquire data from a ground referenced source.I am getting a lots of shot noise which is having a peiodic envope of 55 Hz frequency .These clusters are never removed in all the three modes but the strange thing is that i am having better results in RSE mode than in differential mode for the same source.This looks like a conflicting obervation from what is recomended.What may be the source for these peiodic noise clusters which are unavoidable.
One clue is that we get the same signal if we acquire data between our source ground and earth and same is the case for our computer.This noise is not removed ev
en if we short grounds of PC and our ground reference source.
Attaced is the file having the picture of noise i get.

[Filipe A.]

Hello;

Noise is a difficult issue to advise about.
There are some things you can try, but the result will depend on different factors, such as, environment, lenght of cables, equipment on vicinity, etc.

Anyways, you can try to hook up a BIAS resistor in between the ch- and AIGND on your BNC device. That resistor will bleed out the common voltage current and help on noise balancing. Another thing you can try is to hook up a simple RC low pass filter at the analog input. That might help to get rid of that noise.

I'm also attaching an App Note that talks about Noise and some ways to get around it.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments