I'm trying to use ni usb-6002 to measure a low level DC signal which is around 1.3 V. I used differential set up and two 47k bias resistors. The device is connected to a laptop computer that is connected to a power outlet and is then connected to a wall socket. Here is an actual picture of the connection
However, this gives me really noisy measurement.
the actual signal should be about 1.25V.
and an fft image of it
so it looks like I get all kinds of interference.
However, if I unplug laptop's power, the measurement is much better
and an fft image
I mean if I unplug the power the measurement is much improved but still noisy. I could apply a low pass filter of really low cut-ff frequency and high order, but this would give me unbearable delay and defeat the purpose of real-time monitoring.
So how can I take care of this noise problem? Any help is much appreciated!