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Cathode Ray Oscilloscope A Complete

Basic Guide

An oscilloscope is a type of electronic test instrument that allows observation of constantlyvarying signal voltages, usually as a two-dimensional graph of electrical potential difference

using the vertical or Y axis, plotted as a function of time, (horizontal or X axis). Although

an oscilloscope displays voltage on its vertical axis, any other quantity that can be converted

to a voltage can be displayed as well.

Oscilloscopes are commonly used to observe the exact wave shape of an electrical signal.

Oscilloscopes are usually calibrated so that voltage and time can be read as well as possible

by the eye. This allows the measurement of peak-to-peak voltage of a waveform, the

frequency of periodic signals, the time between pulses, the time taken for a signal to rise to

full amplitude (rise time), and relative timing of several related signals.

Block Diagram

Working Principle

Cathode Ray Oscilloscope works on the following principles:

1. Thermionic emission2. Deflection of the electron beam by the electric and magnetic field.3. Fluorescence produced by the electron beam on a fluorescent screen.

Display & Appearance

The basic oscilloscope, as shown in the illustration, is typically divided into four sections: the

display, vertical controls, horizontal controls and trigger controls. The display is usually a

CRT or LCD panel which is laid out with both horizontal and vertical reference lines referred

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to as the gratitude. In addition to the screen, most display sections are equipped with threebasic controls, a focus knob and an intensity knob.

The vertical section controls the amplitude of the displayed signal. This section carries a

Volts-per-Division (Volts/Div.) selector knob. The horizontal section controls the time base

or sweep of the instrument. The primary control is the Seconds-per-Division (Sec/Div.)

selector switch.

Probes

Open wire test leads are likely to pick up interference,

so they are not suitable for low level signals.Furthermore, the leads have a high inductance, so they

are not suitable for high frequencies. Using a shielded

cable is better for low level signals. Coaxial cable also

has lower inductance, but it has higher capacitance.

Applications

The most frequent use of oscilloscope is use in laboratory experiments. Electricians use them

to view signal voltages, usually as a two-dimensional graph of one or more electricalpotential differences (vertical axis) plotted as a function of time or of some other voltage

(horizontal axis).

Oscilloscopes are used in the sciences, medicine, engineering, and telecommunicationsindustry. General-purpose instruments are used for maintenance of electronic equipment and

laboratory work. Special-purpose oscilloscopes may be used for such purposes as analyzing

an automotive ignition system, or to display the waveform of the heartbeat as an

electrocardiogram. Some computer sound software allows the sound being listened to be

displayed on the screen as by an oscilloscope.

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Calculation of Different Values

Peak to Peak Voltage

Voltage is shown on the vertical y-axis and the scale is determined by the Y AMPLIFIER

(VOLTS/CM) control. Usuallypeak-peak voltage is measured because it can be read

correctly even if the position of 0V is not known. The amplitude is half the peak-peak

voltage.

Voltage = distance in cm volts/cm

Example: peak-peak voltage = 4.2cm 2V/cm = 8.4Vamplitude (peak voltage) = peak-peak voltage = 4.2V

Time Period and Frequency

Time is shown on the horizontal x-axis and the scale is determined by the TIMEBASE(TIME/CM) control. The time periodis the time for one cycle of the signal. Thefrequency is

the number of cycles per second, frequency = 1/time period

Time = distance in cm time/cmExample: time period = 4.0cm 5ms/cm = 20ms

and frequency = 1/time period=1/20ms = 50Hz

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