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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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