# Interpreting an oscilloscope waveform

Discussion in 'General Electronics Chat' started by kminnich, May 19, 2017.

1. ### kminnich Thread Starter New Member

May 19, 2017
2
1
Hi, I am just learning about electronics in general so I can have a better understanding of how things work. I built a cheap, pocket oscilloscope (DSO-068) from China and have been trying to get the hang of how to use it. This . .is a screen shot of a 6.9 VAC waveform that I captured with it.
The items marked in red on the image are my interpretation of the display for the 6.9VAC input signal.
I have two questions: (1) am I interpreting the screen correctly and (2) Why is the display voltage > 10VAC and -10VAC when the input is 6.9VAC?
Note: Since the display only has six vertical divisions, I am using a 10X probe.

I realize that this is not the best of scopes but I think it will suit my needs for learning simple circuits.

Aug 27, 2009
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3. ### #12 Expert

Nov 30, 2010
17,302
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The peak voltage of a 6.9 RMS sine wave is 9.758 volts.
rms x sqrt2 = Vpeak

4. ### drc_567 Senior Member

Dec 29, 2008
263
31
Your time base would be in milli-seconds.
Your line frequency would then be:
$f=1/[(16.3)*10^{-3}]=61.3 Hz$

5. ### crutschow Expert

Mar 14, 2008
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3,813
The vertical scale on an oscilloscope is just volts (V) not VAC, since it can respond to either an AC and/or a DC signal depending upon the input coupling setting.

ms is milliseconds, us or μs would be microseconds.

6. ### kminnich Thread Starter New Member

May 19, 2017
2
1
Thanks to all that responded. I was unaware of the RMS factor so now when I look at a sine wave I will know how to derive the value from it(nsas & #12). I also learned that a DSO plots VOLTS not VAC/VDC(crutschow) which makes a lot of sense and as a bonus drc_567 showed me how to compute the frequency from the plot! I am assuming that my interpretation of the display was accurate (except for the VAC labels) and that the DSO produces fairly accurate results.

Thanks again -- I'll be back!

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