Specifications

7
What Is an Oscilloscope and Why Do You Need One? (continued)
An oscilloscope’s purpose
An oscilloscope’s purpose
An oscilloscope is a measurement
and testing instrument used to
display a certain variable as a
function of another. For example,
it can plot on its display a graph
of voltage (y-axis) versus time
(x-axis). Figure 10 shows an
example of such a plot. This
is useful if you want to test a
certain electronic component
to see if it is behaving properly.
If you know what the waveform
of the signal should be after
exiting the component, you can
use an oscilloscope to see if the
component is indeed outputting
the correct signal. Notice also
that the x and y-axes are broken
into divisions by a graticule. The
graticulte enables you to make
measurements by hand, although
with modern oscilloscopes, most
of these measurements can be
made by the oscilloscope itself.
An oscilloscope can also do more
than plot voltage versus time.
An oscilloscope has multiple
inputs, called channels, and each
one of these acts independently.
Therefore, you could connect
channel 1 to a certain device
and channel 2 to another. The
oscilloscope could then plot the
voltage measured by channel 1
versus the voltage measured by
channel 2. This mode is called
the XY-mode of an oscilloscope.
It is useful when graphing I-V
plots or Lissajous patterns where
the shape of these patterns tells
you the phase difference and the
frequency ratio between the two
signals. Figure 11 shows examples
of Lissajous patterns and the
phase difference/frequency ratio
they represent.
Figure 10. An oscilloscope’s voltage versus time display of a
square wave
180 degrees; 1:1 ratio
90 degrees; 1:1 ratio
90 degrees; 1:2 ratio 30 degrees; 1:3 ratio
Figure 11. Lissajous patterns
Oscilloscope Fundamentals