How does an O-scope measure multiple waves with one probe? 1

[cmb042]

I recently saw something on an oscilloscope that made me wonder how an oscilloscope works. It was a step function, with each step boxed off, having 4 sides. Plus there was a diagonal line inside each box.

The way I understand it, a digital O-scope would sample the probe and should only find 1 voltage. So the scope should read a continuous line. If multiple signals are on one line, then the scope should display the sum. How could the scope display 3 different voltages at one time? I have seen this type of thing before, but never thought about it.

Attaching a snip of a bad picture I took of the scope with my phone.

 

[Skogsgurra]

What you see are several different waveforms superimposed. If you adjust the holdoff to avoid multiple triggering - or use single sweep - you will see one wave. No boxes.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[IRstuff]

Or, you could be seeing aliasing. When the sampling rate is lower than the actual signal frequency, you can get aliased frequencies that might show up on the scope display.

TTFN

FAQ731-376