Device Noise handling

[fitchkor]

I am using the NI USB_6001 DAQ. By wiring the DAQ to itself (AI 0+ & (AI 4-)) and running a differential measurement without a power supply I am getting a noise reading that switches between  -0.0002 V and -0.0015 V. Resulting in -1.3 mV noise being in the device alone. When trying to get a reading of 5V from a power supply I am getting readings that switch between 4.9956 V and 4.9943 V. Again that 1.3mV switching. 

Is there a way, perhaps in LabView, to set up something that will measure the internal noise by wiring a short wire from pins AI 3 and AI 7, running a differential measurement on those pins to get the device noise with no voltage being supplied. And then to read pins AI 0 and AI 4 and subtract the device noise from the results of the voltage read? 

Is there a way to measure the device noise and filter it out from the voltage read? 

I am trying to read as close to a flat DC line as possible. 

I have read the Field Wiring and Noise Considerations for Analog Signals a couple of times and already aware that I am using a Grounded signal source (power supply) and a differential measuring system (DAQ). I know that this can cause a Ground-loop noise to be present. I have tried numerous different wires and different wire lengths with no change. I also am aware that there is some miniscule noise variation when my laptop charger is plugged in vs not plugged in.  

Any insight would be greatly appreciated.

[mcduff]

Maybe I am mistaking something here, but according to the specs you have 14 bits at +/-10 volts range. So 20/2^14 equals 1.2 mV; it sounds like you have a bit flopping back and forth. That is part of the read noise and no way to get rid of it.

mcduff

[fitchkor]

@Mcduff  & @Kevin_Price

That is a very good point, and kind of what I had assumed would be the case. 

I am just thinking of possibly doing a code that would first read the internal values (wire connected from AI 3 and AI 7) and get those values and export to say an excel sheet. Then to take the external voltage reading (AI 0 & AI 4 connected to power supply) and export those values to the same excel. Take the difference of the two and replot. 

But as far as the capabilities of the DAQ being reached, I feel like you guys are right.

[Kevin_Price]

I think my suggestion in the other thread to oversample and average will be both more effective *and* more true than your plan to measure and subtract the short-circuit noise on a different differential channel pair.

-Kevin P