# Interpreting an oscilloscope waveform

#### kminnich

Joined May 19, 2017
2
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.

#### nsaspook

Joined Aug 27, 2009
12,758

#### #12

Joined Nov 30, 2010
18,224
The peak voltage of a 6.9 RMS sine wave is 9.758 volts.
rms x sqrt2 = Vpeak

#### drc_567

Joined Dec 29, 2008
1,156
Your time base would be in milli-seconds.
Your line frequency would then be:
$$f=1/[(16.3)*10^{-3}]=61.3 Hz$$

#### crutschow

Joined Mar 14, 2008
34,019
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.