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# ELE243 Chapter 4: Cathode Ray Oscilloscope (CRO)

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@TemptingAestheticism1951

### What is the primary function of an oscilloscope?

• To display waveforms and other phenomena (correct)
• To convert physical quantities into currents
• To measure voltage only
• To generate ramp voltages
• ### What determines the CRO display?

• A beam of protons
• A beam of neutrons
• A beam of electrons (correct)
• A beam of light
• ### What is the purpose of the horizontal input voltage?

• To move the luminous spot up and down
• To generate a ramp voltage (correct)
• To measure voltage
• To display the waveform of the input voltage
• ### What physical quantities can be converted into voltages using transducers?

<p>Voltage, current, power, pressure, and acceleration</p> Signup and view all the answers

### What is the result of the luminous spot moving in the horizontal direction?

<p>The luminous spot creates a two-dimensional display</p> Signup and view all the answers

### What is the vertical input voltage in a CRO?

<p>The voltage to be measured</p> Signup and view all the answers

### What is the function of the cathode ray tube (CRT)?

<p>To generate an electron beam, accelerate it, and deflect it to create an image</p> Signup and view all the answers

### What is the purpose of the Time Base?

<p>To generate the sawtooth voltage required to deflect the beam</p> Signup and view all the answers

### What is the function of the Trigger Circuit?

<p>To convert the incoming signal into trigger pulses</p> Signup and view all the answers

### What is the function of the Power Supply?

<p>To provide two voltages, a -ve High Voltage (HV) supply and a +ve Low Voltage (LV) supply</p> Signup and view all the answers

### What is the function of the Vertical Amplifier?

<p>To amplify the signal in the vertical section</p> Signup and view all the answers

### What is the range of the +ve voltage supply?

<p>From +300 to +400 V</p> Signup and view all the answers

### What is the range of the –ve high voltage supply?

<p>– 1000 to – 1500 V</p> Signup and view all the answers

### What is the purpose of the electron gun assembly in a CRT?

<p>To generate an electron beam</p> Signup and view all the answers

### What is the effect of the horizontal deflection plates on the electron beam?

<p>It moves the beam horizontally</p> Signup and view all the answers

### What is the purpose of the phosphor coated screen in a CRT?

<p>To display a bright spot</p> Signup and view all the answers

### What is the function of the deflection plates in a CRT?

<p>To deflect the electron beam</p> Signup and view all the answers

### What is the purpose of the evacuated glass tube in a CRT?

<p>To allow the electrons to move freely</p> Signup and view all the answers

### What shape can a Lissajous Figure take, depending on the phase and amplitude of the two signals?

<p>A straight line, an ellipse, or a circle</p> Signup and view all the answers

### What can be understood from the Lissajous Figure obtained by applying a known frequency to the horizontal input and an unknown frequency to the vertical input?

<p>The relationship between the two frequencies</p> Signup and view all the answers

### How can the unknown frequency be measured using the Lissajous Figure?

<p>By using the formula: fV = (No. of loops cut by horizontal line) / (No. of loops cut by vertical line) * fH</p> Signup and view all the answers

### What can be calculated from the amplitudes A and B of the Lissajous pattern?

<p>The phase difference between the signals</p> Signup and view all the answers

### What is the shape of the Lissajous pattern when measuring the phase difference between two sinusoidal signals of the same frequency?

<p>An ellipse</p> Signup and view all the answers

### What determines the shape of the Lissajous Figures?

<p>Amplitude, phase difference, and ratio of frequency of the two waves</p> Signup and view all the answers

### What does the Volts/div. control do?

<p>Selects the desired voltage sensitivity of the vertical amplifier</p> Signup and view all the answers

### What is the purpose of the Horizontal Position knob?

<p>To move the trace up or down on the screen</p> Signup and view all the answers

### What does the Sweep time/cm Variable control do?

<p>Provides continuously variable sweep rates</p> Signup and view all the answers

### What does the Level control do?

<p>Selects the voltage point on the triggering signal at which the sweep is triggered</p> Signup and view all the answers

### What is the purpose of the Trigger Controls?

<p>To select the timing of the beginning of the horizontal sweep</p> Signup and view all the answers

### What is the function of the Horizontal Variable control?

<p>To control the attenuation of the signal applied to the horizontal amplifier</p> Signup and view all the answers

## Study Notes

### Cathode Ray Oscilloscope (CRO)

• A CRO is an instrument that measures, displays, and analyzes waveforms and other phenomena in electronic and electrical circuits.
• It can display the amplitude of many electrical signals, such as voltage, current, power, pressure, and acceleration, primarily as a function of time.
• CROs operate on voltages, and other physical quantities are converted into voltages using transducers to present their visual representations.

### Principle of Operation

• A beam of electrons produces a luminous spot on a fluorescent screen, creating a two-dimensional display when deflected in either of the two orthogonal axes (X and Y).
• The horizontal input voltage is an internally generated ramp voltage called the time base, which causes the luminous spot to move horizontally from left to right.
• The voltage to be measured is applied as a vertical input, causing the luminous spot to move up and down with respect to the instantaneous value of the vertical voltage.

### Block Diagram of Cathode Ray Oscilloscope

• The cathode ray tube (CRT) generates an electron beam, accelerates it to a high velocity, and deflects the beam to create an image.
• The vertical amplifier amplifies signals in the vertical section.
• The delay line delays the signal for some time in the vertical section.
• The time base generates the sawtooth voltage required to deflect the beam in the horizontal section.
• The horizontal amplifier amplifies the sawtooth voltage before it is applied to the horizontal deflection plates.
• The trigger circuit converts the incoming signal into trigger pulses to synchronize the input signal and sweep frequency.
• The power supply provides two voltages: a +ve low voltage supply (from +300 to 400 V) and a –ve high voltage supply (from –1000 to –1500 V).

### Cathode Ray Tube

• A CRT is a glass tube consisting of an assembly of electrodes, including a phosphor-coated viewing screen, electron gun assembly, deflection plates, and a base.
• The electron gun assembly generates a sharp, highly focused electron beam, which is accelerated to a high velocity.
• The beam passes through the deflection plates, which supply an operating voltage to deflect the beam, and then hits the phosphor-coated screen to create a bright spot.

### Deflection Systems

• Electrostatic deflection of an electron beam is used in a general-purpose oscilloscope.
• The deflecting system consists of a pair of horizontal and vertical deflecting plates.
• The plates cause the beam to move horizontally and vertically, creating a two-dimensional display.

### Applications of CRO

• Measurement of frequency using Lissajous figures: 𝑓𝑉 No.of loops cut by horizontal line = 𝑓𝐻 No.of loops cut by vertical line
• Measurement of phase difference using Lissajous figures: 𝜑 = sin−1 (𝐴/𝐵)

### CRO Controls

• Vertical controls: Volts/div., Volts/div. Variable, and Vertical Position knob
• Horizontal controls: Sweep time/cm, Sweep time/cm Variable, Position, and Horizontal Variable
• Trigger controls: Slope, Coupling, Level, and automatic (auto) triggering or free run

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## Description

Measurements and Instrumentation quiz, covering the Cathode Ray Oscilloscope (CRO), an instrument used to measure, display, and analyze waveforms and other phenomena in electronic and electrical circuits.

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