CATHODE RAY OSCILLOSCOPE

TOPICS COVERED Introduction to CRO Block diagram of CRO Detailed description of CRT Multi –Input Oscilloscope Lissajous Patterns Types of Oscilloscope and it’s application

HOW A CRO LOOKS LIKE

INTRODUCTION TO CRO

Versatile electronic instrument giving visual display of signals

Used for measurement of frequency , amplitude, phase etc.

Also used in determining the nature and characteristics of various components.

Has a high bandwidth range thus making it a sensitive and accurate device.

Easier to use as the internal routine act as a guide to the user.

BASIC DIAGRAM

ANOTHER SCOOP….

WORKING OF A CRO

CATHODE RAY TUBE

The main parts of Cathode Ray Tube are: Electron Gun Assembly Focusing Anodes Deflection Plates

Assembly Screen for CRT

Electr

on G

un

Anodes

Deflection Plates

Fluorescent Screen

Multi-Input OscilloscopeOscilloscope can have multiple input and display facilities.

The most common one is of - TWO INPUTS.

Although FOUR and EIGHT inputs are available for special applications

There are primary two types of multi-input oscilloscope :-

Single Beam Oscilloscope

Dual Beam Oscilloscope Both of them can be converted into a further Number of traces.

Dual Trace Oscilloscopes

In this oscilloscope two separate vertical input channels are used.There are two common operating modes for the Electronic Switch, called Alternate and Chop which can be selected from the instrument’s front panel.

Dual Trace Oscilloscopes

BLOCK DIAGRAM

Dual Beam OscilloscopeThe Dual Beam Oscilloscope has two separate electron beams , and therefore two completely separate vertical channels.

There are two methods used for generating the two electron beams within the CRT. The first method is :-

Double gun tube

Split Beam

Multiple input CRO works in following two modes

• alternate mode• chopped mode

Alternate mode

In alternate mode the an electronic switch alternates between sig A & B.

Waveform in alternate mode

Chopped modeIn the chopped mode the switch free runs at very high frequency.

Waveform of Chopped Mode

PatternWhen two sinusoidal voltage signals of equal frequency having some phase difference are applied to the deflection plates of CRO, a straight line or an ellipse appears on the screen these figures are called Lissajous figures or Lissajous curves or pattern.

Some examples of lissajous figures……..

With the help of lissajous figures we can measure…….

FrequencyPhase

Frequency Measurement Fx/Fy = Hp/Vp

Fx = Unknown frequencyFy = Known frequencyHp = Points on horizontal tangenciesVp = Points on vertical tangencies

Phase Measurement

sin Ф = c/b

Digital Storage Oscilloscope

BLOCK DIAGRAM OF DSO

Advantage Of DSOStores waveform for infinite time

Digitize waveform can be processed in any way

Writing speed is more

Processing of signal is easy

Analog Storage Oscilloscope

Trace storage is an extra feature

They used direct-view storage CRTs

The storage is accomplished using the principle of secondary emission

Briefings

Data can be stored to infinite time

Image quality is good

Writing speed is high

Processing of signal is easy

Data can be stored for finite time

Image quality is not poor

Writing speed is poor

Processing of signal is difficult

Difference between ASO & DSODSO

ASO

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