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AUTOMOTIVE INSTRUMENTATION 9

circuits, a relatively simple overview of the functional operation of the CRT as a
display device is straightforward and should serve to illustrate some potential
automotive applications.
Figure 9.20 is a sketch of a typical CRT. It is an evacuated glass tube that
has a nominally flat surface that is coated with a phosphorescent material. This
surface is the surface or face on which the displayed messages appear. At the rear
is a somewhat complex structure called an electron gun. This device generates a
stream of electrons that is accelerated toward the screen and brought to
convergence at a spot on the screen. A system of coils in the form of
electromagnets causes this convergence of electrons (or beam) and is referred to
as the magnetic focusing system. The focused stream of electrons is called the
beam.
The electron beam generates a spot of light at the point on the screen.
The intensity of the light is proportional to the electron beam current. This
current is controlled by the voltage (V ), which is called the video signal, on an
c
electrode that is located near the electron gun.

Figure 9.20
CRT and
Associated
Circuitry

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 319