09-27-2016 06:11 AM
We re trying to acquire 1mV sinusoidal signals with a NI6124 card
(differential inputs), through a BNC 2090 rack interface.
Input dynamic is -5 +5 V.
Terminal configuration is RSE.
Only one input is connected.
It seems signal distortion (>10%) , dissymetry (> 25%) ,and amplitude modulation, appears below 10mV. Example snapshots are attached.
Signal is ok on a parallel scope.
Would terminal configuration or input dynamic have an impact on that ?
Is there any other reason why we would observe such distortion/dissymetry ?
Thank you for your answers.
Regards.
Charles.
09-27-2016 07:04 AM
1) why RSE not differential?
2) count 50/60HZ on graphs, AM maybe from power wires.
3) why +-5V, not +-1?
09-28-2016 04:00 AM
As said, busy trying +-1 V range, for better sampling resolution.
However, if I understood well, measurement could be more impacted
by signal offset in that case, since we're closer to max amp gain.
also trying BNC 2090 differetial set up.
I hope we get better measurement in that case.
Why RSE ?: We try to get best equipotential at PXI input , RSE gathers all
negative signals to ground.
I'm reading at least 10kHz for AM in the snapshots, wonder how you count 50Hz.
Thank you .
Charles.