5122 noise of 50 mV

[aparab]

Hi all,

I am using a 5122 Oscilloscope/ digitizer.

I am measuring a DC signal  but have noise  of about 50 mV (see  attachment  Vertical Range is 100mV)

the Signal is 0V from a  DC Source. 

The source is clean is it that the  5122 is inducing noise ....

My goal is to measure a 20Khz 500mV AC signal  with 2,5 V DC offset.

If I have such  results  for a pure DC signal  , I wonder how I guarantee the accuracy  of my measurements

[Nathan-P]

Not sure where the noise is comming from, have you tried running self-calibration?  See the VI below, or you can run it from MAX.

http://zone.ni.com/reference/en-XX/help/370592N-01/scopeviref/niscope_cal_self_calibrate/

Also, you can verify the performance of your hardware by checking against the accuracy formula in the specifications documentation:

http://digital.ni.com/manuals.nsf/websearch/C6B059C1BDD70101862574C8005567F1

Also, 100mV is an invalid vertical range for the NI 5122, and it is cohercing your vertical range up to the next supported range which is 200mVpp.

Regards,

Nathan

PS. the accuracy of the measurement of your goal is as follows (add DC accuracy to Vertical offset accuracy):

1Vpp range

+-((0.65% * 500mV + 1.2mV) + 0.4 * 2.5V) = +- ~15mV

[Henrik_Volkers]

After configuring the scope insert a commit and after that, read the properties of the actual range and the actual samplerate!

(Or RTFM and choose only valid settings 😉 )

Have you done noise measurements without anything connected to the inputs? (Do it with 1 MOhm and 50 Ohm input impedance)

Do that again with your cable to the DC supply , but not connected to the supply, again but only with GND/Shield connected .

Sample 100ms with the highest possible samplerate. How does the power spectrum look like?

If you explain more about the task you want to do, more hints (and maybe tricks) are possible.

(For exampe, if you measure a sine, try the tone detction vi or a sine approximation. This is a narrow band signal analysis , quite immune against noise 😉 , but blind against nonlinearities)

[aparab]

Thanks Nathan 

Danke Henrick (Ich probiere dass)