set up across the deflection plates by a deflection voltage.
The progressive
deflection of the beam paints the picture of the waveform on the face of the
a. The inner face of the CRT is coated with a material which fluoresces when
it is struck by the beam of electrical energy. In the CRT the beam is repeatedly
swept across the screen. With the waveform, an alternating-current voltage can be
observed on the screen when it is applied to one pair of deflection plates and when
a second voltage of appropriate characteristics is simultaneously applied to the
other pair of plates.
b. The conventional way of representing voltage or current of a sine waveform
is shown in Figure 2-1. The voltage to be observed is applied between the vertical
deflection plates; simultaneously, a sawtooth voltage is applied between the
horizontal deflection plates.
The sawtooth voltage moves the beam from left to
right at a constant speed to form the time scale along line OX (fig 2-1). Then it
returns the beam rapidly to the starting position at the left, and repeats the
operation. The sawtooth voltage is so named because it resembles a sawtooth. As
the voltage increases from A to B, the beam is swept from 0 to 12. As the voltage
falls from B to C, the beam is quickly returned to its starting position (zero),
and the process is repeated.
c. If an AC voltage of sine waveform is applied between the vertical
deflection plates with no horizontal deflection, a single vertical line appears on
the screen.
The varying rate of change of the voltage is hidden because the
vertical movements retrace themselves repeatedly on the same vertical line.
Similarly, if a sweep voltage of sawtooth waveform is applied to the horizontal
deflection plates in the absence of vertical deflection, a horizontal line is
formed, and the rate of change of the voltage is obscured.
However, when both
voltage are introduced at the same time, the vertical motion of the beam is spread
out across the screen to form a sine curve, such as the one shown in Figure 2-1.
Figure 2-1.
Sinewave and sawtooth voltage waveforms
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