are there system signals in USB-6008?

[LSPRMEMS]

I use DAQ with photodetector to see light intensity change in Biosensing system.

I set sampling rate to 1KS/s and +10 to -10 voltage range.

As you can see in the graph(upper one) I attached, there are signals like impulse ( they are exactly 10mV) 

That signals are always exist on the some voltage level.

I don't know what it is. I guess that are not noises because that have exactly 10mV. 

[johnsold]

In single ended mode the USB-6008 has a resolution of 9.766 mV.  The system noise is specified as 5 mV rms. It is not unreasonable to expect that you are seeing an occasional 1 LSB jump due to noise.

I would consider this normal for that device.

Lynn