Specifications

The sine wave's amplitude in Figure 2 is shown as the distance ‘A’. The mathematical expression for

the sine wave, expressing the voltage as a function of time, is:

= sin()

From the graph, you can see that the period of this sine wave is 6.2 ms. This corresponds to a

frequency of 1/(6.2 x 10

-3

s) or 161 Hz. Then we have = 2= 2

(

161

)

= 1011 radian/s. We can

also read from the graph that the sine wave's amplitude ‘A’ is 3.2 volts. Thus, the equation for this

particular sine wave is:

= 3.2sin(1011)

where t is measured in seconds and V is measured in volts. Here is a graph from an oscilloscope

showing such a sine wave produced by a function generator:

Figure 3

Amplitude measurements

A common measurement of a waveform on an oscilloscope's graph is the peak-to-peak amplitude. This

is the vertical distance from the minimum point to the maximum point on the waveform. Here you can

see that the minimum point is at -3.3 divisions, measured from the V = 0 axis marked by the yellow 1

and arrow marker on the left. The maximum point is at +3.1 divisions. Hence, the peak-to-peak

amplitude is 3.1 - (-3.3) or 6.4 divisions. The scope's vertical channel gain is set to 500 mV per division,

so we get a measured peak-to-peak voltage of (6.4 div)x(500 mV/div) = 3.2 volts. Note this

measurement is shown by the scope in the lower left corner of the picture and demonstrates that some

scopes can be set up to display various waveform measurements of interest.

The period of the waveform is calculated from the two intersections with the V = 0 axis. The first one is -

3.2 divisions and the second one is 3.1 divisions. The scope's horizontal axis (called the timebase or

sweep speed) is set to 1 ms/div. Thus, the period is [(3.1 div) - (-3.2 div)]x(1 ms/div) = 6.3 ms. The

frequency is the reciprocal of this or 159 Hz. The scope has also provided this measurement at 161 Hz.

Our measurement from the screen disagrees from the scope's measured value by roughly a percent.

We'll have more to say about this later -- but one of the key things to realize about the measurements

made from an oscilloscope's screen is that you can, at best, expect a measurement resolution and

accuracy of a few percent.

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