Electronic – How much background “noise” is normal on an oscilloscope


Following this question, I purchased a DSO-2090 USB oscilloscope.

When I power it up, I see lots of small fluctuations in the waveform, whether connected to nothing, a battery source, itself (small waveform generator on the back) or by shorting the ground clip.

Oscilloscope Noise

(See the large version)

In the screenshot above, the CH1 is connected to a small, battery powered circuit of mine. CH2 does not have the probe connected at all.

I have spoken to a colleague about this and was told that I should see a flat line so I am worried I have purchased a faulty unit.

My question is whether or not background noise like this is normal in an oscilloscope?

Edit 1

Added 1kHz waveform example as per comment:


(See the large version)

Best Answer

As an indicator that the second capture you displayed looks normal, here's one I just made of a 1 KHz square wave, from my ELAB-080 combination instrument (dual channel DSO, 16-channel logic analyzer, arbitrary waveform generator (AWG), and dual channel power supply) which also has a vertical 8-bit resolution in its DSO section. (Note: at $495, the ELAB-080 was over your budget in your other question where I recommended the DSO-2090).

You can see the noise at the top and bottom of each square wave, which looks almost identical to your trace.

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