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CALIBRATION AND APPLICATION OF CATHODE RAY OSCILLOSCOPE IN OUR LABORATORY

(Science Lab Technology)

CALIBRATION AND APPLICATION OF CATHODE RAY OSCILLOSCOPE IN OUR LABORATORY

ABSTRACT

The cathode ray Oscilloscope plays a very important role in the laboratories, for instance it is used to measure frequency and voltage of a signal it is equally used for study current fluctuation in electric power supply the cathode ray oscilloscope is made up of three major part, they are the cathode ray tube, which is the major integral part A the Oscilloscope also the other important[1 parts of the Oscilloscope is the power supply unit and the vertical as well as horizontal amplifier. Some of the cathode ray oscillioscope are calibrated manually while some are already calibrated by the manufacturers.  The subpart of the oscilloscope which include Cathode Ray Tube   (CRT) is made of three (3) major parts namely the electron gun which produces electron before acceleration and the second sub part of the instrument in the deflecting plates which helps to deflect the electron towards the screen where it is seen.  This cathode Ray Oscilloscope works in the principle that the signal to be displayed is amplified by the vertical amplifier and applied to the vertical deflection plates of the CRT, a portion of the signal in the vertical amplifier is applied to the sweep trigger as a triggering signal.  Then the sweep trigger generates a pulse coincident with a selected point in the cycle of the triggering signal.  This pulse turns on the sweep generator. Initiating the saw-tooth wave form.

TITLE PAGE

CHAPTER ONE

1.0        Introduction                                                       

1.1    The Background Review of the Cathode Ray Oscilloscope                                                 

1.2    Limitations of the Study                                       

1.3    Objective of the study                                 

1.4    Definition of Terms                                             

CHAPTER TWO

2.1        Mode of operation of Cathode Ray Oscilloscope

2.2        Scheme Diagram of CRO                                     

2.3         The Parts of Cathode Ray Oscilloscope (CRO)

2.4        Schematic Diagram of Cathode Ray Tube       

2.4.1          The pars of Cathode Ray (CRT)                 

2.4.2          Vertical Amplifier                                            

2.4.3          Delay Line                                                     

2.4.4          The Power Supply Section                                

2.4.5          Time Base Generator                                      

2.4.6          Horizontal Sweep Section                         

CHAPTER THREE

3.0    Calibration and setting up of cathode Ray

Oscillioscope                                                      

3.1    Setting of Cathode Ray Oscilloscope              

3.2    The Summary for setting up CRO                  

3.3    Calibration of Cathode Ray Oscilloscope         

CHAPTER FOUR

4.0    Application of Cathode Ray Oscilloscope in

 Laboratory                                                       

4.1    CRO as a voltmeter                                            

4.2    Frequency Measurement with CRO                

4.3    Measurement of Voltage and Time Period       

CHAPTER FIVE

5.0        Summary, Conclusion and Recommendation   

5.1    Summary                                                  

5.2    Conclusion                                                 

5.3    Recommendation                                               

REFERENCES                                                                       

CHAPTER ONE

1.0  INTRODUCTION

1.1    THE BACKGROUND REVIEW OF THE CATHODE RAY OSCILLIOSCOPE

The cathode Ray oscilloscope (CRO) is an extremely useful and versatile laboratory instrument used for measurement and analysis of wave forms and other phenomenon in electronic acts.  It provides a means of observing time varying voltages, it can present a visual representation of dynamic phenomena by means of transducers that converts current, pressure, strain, temperature, acceleration and many other physical quantities into voltages.

Recording of what is happening in oscilloscope can be made by a special camera attached to the cathode ray oscillioscope (CRO) for quantitative interpretations (keith, 1995).

Paul (2000) stated that cathode- ray oscilloscope (CRO) is a device e which displays a graph of an electrical signal on the face of a cathode ray tube. This is usually done by displaying a time-varying potential (voltage) potential (voltage) on the vertical axis (y), anytime on the horizontal axis. This is called the “y-t” mode. Most oscilloscope also allow the horizontal axis to be driven with another time varying potential.  In this mode, the horizontal axis is called the x- axis, and this is called the x-y mode common with the Cathode Ray Tube (CRT) has much in tube of the TV sets. A hot wire filament heats a metal cathode which then emits electrons. These electrons are accelerated by a high potential (typically 10kv), collimated in to a narrow beam and focused to a small spot on the front of the Cathode Ray Tube (CRT). They give up their energy to the atoms in the phosphor coating on the front of the tube.  These excited atoms quickly give up their energy in the form of light.  Thus, the small spot struck by the election beam give off visible light.  The struck by electron beam give off visible light.  The beams is aimed as a particular spot on the phosphor screen by two pair of electrostatic deflecting plates, one set to deflect the beam up or down and the other to deflect the beam left or right (Bruce D, 1969).

The deflecting plates potential are controlled by the output of two independent electronic amplifier while the horizontal amplifier is driven by saw tooth wave generator (within the Oscillioscope).  The saw tooth generator drives the electron beam horizontally at a constant speed, then quickly returns it to sweep again.  The right-to-left motion is usually so rapid that the eye cannot follow the motion, and only the left to right sweep is seen.  The phosphor coating of the screen has persistence which causes it to glow for a short time after being excited. The persistence of the screen and the persistence of the human eye (vision) combine to produce a flicker free illusion of a continuously traced graph (Paul, 2000).

Both the vertical and horizontal amplifier has precisely calibrated gain (Amplitude) controls which makes it possible to determine potential and time intervals accurately from measurements on the face of the CRT.  The sweep generator of the older oscillioscope can only be adjusted in frequency. It is often tricky to stabilize the screen of such a scope.  More sophisticated Oscillioscope also have a “trigger’ mode in which the sweeps is initiated (triggered) by an electric signal.

One can choose whether the triggering signal is Internal or from an EXTERNAL signal.  Usually one can set the sign and size of the voltage required to trigger the sweep.  Some even allow you to choose to trigger on voltage level or on the slope of wave form (Wedlock, 1969).

        Mostly a “time base’ generator.  But oscillioscope generally have some provision to deflect the beam with an external signal modern oscillioscope often have two independent Amplifiers which may be used simultaneously.  Each is called a channel and such an oscillioscope is a “dual channel” oscillioscope.  Dual channel oscillioscope can display two different signals simultaneously on the screen, and may have the capability to display their sum or their differences.

David et al, (2001) highlighted that Cathode Ray oscillioscope (CRO) is a common laboratory instrument that provides accurate time and amplitude measurement of voltage signal over a wide range of frequencies. Its reliability, stability and ease of operation makes it suitable as a general purpose laboratory instrument.  The heart of cathode ray oscillioscope (CRO) is the cathode ray tube.  The cathode ray is a beam of electrons which are emitted by the heated cathode and accelerated towards the fluorescent screen.  The assembly of the cathode, intensity grid, and accelerating anode is called the “ELECTRON GUN”. Its purpose is to generate the electron beam and control its intensity and focus.  Between the electron gun and the fluorescent screen, are two pairs of metal plates. One oriented to provide horizontal and vertical defecting plates.  The combination of these two deflections, allows the beam to reach any portion of the fluorescent screen.  Wherever the electron beam hits the screen, the phosphor is excited and light is emitted from that point.  This conversion of electron energy into lights allows us to write with points of light on an otherwise darkened screen (Roberge, 1969).

In the most common use of the oscillioscope, the signal to be studies is first amplified and then applied to the vertical plates to deflect the beam vertically and at the same time a voltage that increase linearly with time is applied to the horizontal plates thus, causing the beam to be deflected horizontal at a uniform rate.  The signal applied to the vertical plates is thus, displayed on the scream as a function of time.  The horizontal axis serves as a uniform time scale.  The linear deflection or sweep of the beam horizontal is accomplished by use of a sweep generator that is incorporated in the oscillioscope circuitry.  The voltage output of such a generator is that of a saw-tooth as shown in the diagram below:

 

 

 

 

 

 

 

 

 

 

Fig. 1.1  The saw-tooth  like of a sweep generator

        Application of one cycle of this voltage difference, which increase. Linearly with time, to the horizontal plates causes the beam to be deflected linearly with time across the tube face.  When the voltage suddenly fall to zero as at point a, b, and c.  The end of each sweep, the beam flies back to the initial position.  The horizontal deflection of the beam is repeated periodically, the frequency of this periodicity is adjusted by external controls (Kieth, 1995.)

1.2       OBJECTIVE OF THE STUDY

To know the calibration and application of cathode ray oscilloscope in the laboratories.

1.3       DEFINITION OF TERMS

Amplitude: This is the maximum displacement of a particle from its mean position.

Peak Voltage: This is the maximum voltage.

Time Period: This is the time taken for the sign to complete one cycle.

Wave number: This is defined as 2l times the reciprocal of the wavelength (K =2Õ/l).

Wave Velocity: This is the distance a wave signal covers in a given time.

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