Instruction manual

2 Description of How a Scope Displays a Single Periodic Voltage
A periodic function in time is one that repeats itself again and again, such as a sine wave
or a square wave. A scope can display a voltage that is periodic in time in exactly the same
way. The periodic voltage is connected to the vertical input of the scope, and if the scope is
adjusted correctly, a graph of the voltage as a function of time appears as a stationary trace
on the screen of the scope.
Figure 1:
Every scope has a signal generator or time base oscillator. This oscillator produces a
voltage that is a square wave as a function of time. Fig. 2 shows the ramp voltage for one
sweep of the electron beam. This linear ramp, when applied to the horizontal axis of the
scope screen, sweeps the beam from the left side of the screen to the right side of the screen.
When the ramp voltage across the horizontal deflection plates is V
L
, the beam is at the left
of the screen. When the ramp voltage is zero the beam is in the horizontal center of the
screen. When the ramp voltage is V
R
the beam is at the right of the screen. We assume
that |V
L
|=|V
R
|. How quickly the scope signal is swept across the screen is controlled by the
TIME/DIV switch.
Figure 2:
In the most usual mode of operation, the voltage on the horizontal axis is held at V
L
If a
“trigger” pulse is applied to the circuit (source of the trigger pulse discussed in a moment)
2