Cathode Ray Oscilloscope | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) PDF Download

Introduction : 

  • The CRO is a device that allows the amplitude of electrical signals, whether they be voltages, current, power etc. to be displayed primarily as a function of time.
  • The cathode ray oscilloscope (CRO) is a very useful and versatile laboratory instrument used for display, measurement and analysis of waveforms and other phenomena in electrical and electronics circuits.

Cathode Ray Tube (CRT) : 

  • The “Heart of the CRO” is the CRT, which generates the electron beam, accelerates the beam to a high velocity, deflects the beam to create the image and contains the phosphor screen where the electron beam eventually becomes visible.
  •  The main parts of a CRTs are following :
    • Electron gun assembly
    • Deflection plate assembly
    • Fluorescent screen
    • Glass envelope
    • Base

 Cathode Ray Oscilloscope | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Electron gun 

  • The source of focused and accelerated electron beam is the electron gun.
  • The electron gun which emits electrons and forms them into a beam consists of several elements which are given below.

Heating element 

  • Heating element used to heat up the cathode.

Cathode 

  • It is cylindrical shaped with layer of barium and strontium oxide is deposited on the end of the cathode which is to obtain high emission of electrons at moderate temperatures.

Control grid 

  • The control grid is used to control the number of electron emitted from cathode.
  • This control grid is usually a nickel cylinder, with a centrally located hole, coaxial with the CRT axis.
  • The grid with its negative bias controls the number of electrons emitted from the cathode and hence the intensity of electron beam is controlled by the grid.

 Pre-accelerating and accelerating anode:

  • The electrons, emitted from the cathode and passing through the hole in the control grid are accelerated by the high positive potential which is applied to the pre-accelerating and accelerating anode.
  • The pre-accelerating anode and the accelerating anode are connected to a common positive high voltage of 1500 V.

Focusing anode 

  • The electron beam is focusing an electron beam.
    (i) Electrostatic focusing
    (ii) Electromagnetic focusing

Deflecting plates 

  • From figure we observe that the electron beam, after leaving the electron gun passes through two pairs of deflection plates.

Vertical deflecting plates or Y-plates 

  • It is responsible for vertical deflection of electron beam.
  • These plates are supplied with external signal fed via one of the input channel of CRO.

Horizontal deflecting plates or X-plates: 

  • These plates are responsible for horizontal motion of electron beam.
  •  In normal mode of CRO, horizontal plates are connected to output signal of sweep generator which is inside the CRO.
  • For the display of a waveform, horizontal plates are given a saw tooth wave which results into continuous motion electron beam from left to right on the screen.

 Cathode Ray Oscilloscope | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) 

Application of CRO : 

Measurement of voltages and Currents 

  • The electrostatic deflection given in equation shows that the deflection is proportional to the deflection-plate voltage. The value of a current can be obtained by measuring the voltage drop across a known resistance connected in the circuit.
  • Direct voltages may be obtained from the static deflection of the spot, alternating voltages from the length of the line produced when the voltage is applied to Y-plates while no voltage is applied to X-plates. The length of this line corresponds to peak to peak voltage.
  • When dealing with sinusoidal voltages, the rms value is given by dividing the peak to peak voltage by 2 √2.

Measurement of Phase 

  • It is interesting to consider the characteristics of pattern that appear on the screen of a CRT when sinusoidal voltages are simultaneously applied to horizontal and vertical deflection plates. These patterns are called “Lissajous patterns”.

Measurement of Frequency : 

  • Lissajous pattern may be used for accurate measurement of frequency.
  • Frequency of signal with CRO can be determined by operation it in X-Y mode. In this Y-input channel and a signal of known frequency is connected to X-input channel.

The frequency of the signal can be given by using following formula,

  Cathode Ray Oscilloscope | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

where,
fy = unknown frequency
fx = known frequency

also,
Cathode Ray Oscilloscope | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Cathode Ray Oscilloscope | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

where, fy = frequency of signal applied to Y-plates
fx = frequency of signal applied to X-plates

The document Cathode Ray Oscilloscope | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Electrical Engineering SSC JE (Technical).
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FAQs on Cathode Ray Oscilloscope - Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

1. What is a cathode ray oscilloscope (CRO) and how does it work?
Ans. A cathode ray oscilloscope (CRO) is an electronic instrument used in electrical engineering to display and analyze varying signals. It works by generating an electron beam, known as the cathode ray, which is directed towards a screen. The beam is deflected by varying voltages, allowing the display of the signal's waveform.
2. What are the main components of a cathode ray oscilloscope?
Ans. The main components of a cathode ray oscilloscope include an electron gun, vertical and horizontal deflection plates, a screen, and various controls. The electron gun emits electrons, the deflection plates control the movement of the electron beam, and the screen displays the waveform. The controls include settings for adjusting the voltage scale, time scale, and triggering options.
3. How is a cathode ray oscilloscope used in electrical engineering?
Ans. A cathode ray oscilloscope is used in electrical engineering for various purposes. It can be used to measure and analyze electrical signals, such as voltage and frequency. It can also be used for troubleshooting and diagnosing problems in electronic circuits. Additionally, it is used to visualize and observe waveforms, allowing engineers to understand the behavior of electrical systems.
4. What are the advantages of using a cathode ray oscilloscope?
Ans. Some advantages of using a cathode ray oscilloscope include its ability to display and analyze complex waveforms, its high accuracy in measuring voltages and frequencies, and its versatility in troubleshooting electrical circuits. It also allows for real-time observation of signals and provides a visual representation of electrical phenomena, making it easier for engineers to understand and interpret data.
5. What are the limitations of a cathode ray oscilloscope?
Ans. Despite its usefulness, a cathode ray oscilloscope has some limitations. It has a limited bandwidth, meaning it may not accurately display high-frequency signals. It also requires a stable power supply and can be affected by electromagnetic interference. Additionally, it may not be suitable for measuring very low voltage signals or signals with fast rise times.
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