ELE243 Chapter 4 CRO Quiz: Cathode Ray Oscilloscope

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Questions and Answers

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?

Voltage, current, power, pressure, and acceleration Signup and view all the answers

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

The luminous spot creates a two-dimensional display Signup and view all the answers

What is the vertical input voltage in a CRO?

The voltage to be measured Signup and view all the answers

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

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

What is the purpose of the Time Base?

To generate the sawtooth voltage required to deflect the beam Signup and view all the answers

What is the function of the Trigger Circuit?

To convert the incoming signal into trigger pulses Signup and view all the answers

What is the function of the Power Supply?

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

What is the function of the Vertical Amplifier?

To amplify the signal in the vertical section Signup and view all the answers

What is the range of the +ve voltage supply?

From +300 to +400 V Signup and view all the answers

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

– 1000 to – 1500 V Signup and view all the answers

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

To generate an electron beam Signup and view all the answers

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

It moves the beam horizontally Signup and view all the answers

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

To display a bright spot Signup and view all the answers

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

To deflect the electron beam Signup and view all the answers

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

To allow the electrons to move freely Signup and view all the answers

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

A straight line, an ellipse, or a circle 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?

The relationship between the two frequencies Signup and view all the answers

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

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

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

The phase difference between the signals 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?

An ellipse Signup and view all the answers

What determines the shape of the Lissajous Figures?

Amplitude, phase difference, and ratio of frequency of the two waves Signup and view all the answers

What does the Volts/div. control do?

Selects the desired voltage sensitivity of the vertical amplifier Signup and view all the answers

What is the purpose of the Horizontal Position knob?

To move the trace up or down on the screen Signup and view all the answers

What does the Sweep time/cm Variable control do?

Provides continuously variable sweep rates Signup and view all the answers

What does the Level control do?

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

What is the purpose of the Trigger Controls?

To select the timing of the beginning of the horizontal sweep Signup and view all the answers

What is the function of the Horizontal Variable control?

To control the attenuation of the signal applied to the horizontal amplifier 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.

ELE243 Chapter 4: Cathode Ray Oscilloscope (CRO)

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