Physics and Engineering of Radiation Detection

742 Appendix-A A. Essential Electronic Measuring Devices

Attenuator

Vertical Deflection System

Fluorescent

Screen

Electrons

Generator

Sweep

Trigger System

Measurement

Lead

Electron

Gun

Horizontal Deflection System

Amplifier

Horizontal

Amplifier

Vertical

Figure A.2.1: Main components of a typical analog oscilloscope.

A.1 Attenuator

The role of attenuator is to reduce the signal amplitude according to a factor set by
the user. This effectively allows the user to zoom-in the signal trace on the CRT
display.

A.2 ElectronGun..........................

The electron gun is the source of electrons that are used to create the image on
the fluorescent screen. It is typically made of a filament that emits electrons when
heated. In the absence of an electric field, these electrons would form a cloud around
the filament. However the CRT is provided with a high potential gradient, which
directs these electrons to the fluorescent screen. It should be noted that production
of electrons is not initiated by the input signal. In fact, neither the production of
electrons nor their intensity is dependent on the presence of signal at the oscilloscope
input. Whenever the oscilliscope is turned on, the filament gets heated and starts
emitting electrons.

A.3 ElectronBeamDeflectionSystems

The variation in the input voltage with time is displayed as a waveform in an oscillo-
scope. Generation of this waveform requires deflection of the electron beam in both
vertical and horizontal directions. The vertical position at any instant in time is
proportional to the input voltage at that time, while the horizontal position carries