Construction of CRO MCQ Quiz - Objective Question with Answer for Construction of CRO - Download Free PDF

The correct answer is: 1) The propagation speed of the signal in the line

Explanation:

In an electrical delay line used in oscilloscopes, the delay time is determined by:

• The physical length of the delay line

• The propagation speed of the signal through the line (which depends on the medium's properties, such as its dielectric constant and inductance/capacitance per unit length).

Option Analysis

2. The resistance of the delay line → Affects signal attenuation, not the delay time.

3. The frequency of the input signal → The delay line is typically designed to be frequency-independent for a wide range of signals.

4. The speed of the electron beam → This relates to the CRT display, not the delay line.

Thus, the correct choice is 1) The propagation speed of the signal in the line.

Explanation:

Measuring Time Delay in an Oscilloscope

Definition: An oscilloscope is an electronic instrument used to measure and visualize varying electrical signals. It displays the waveform of the signal, allowing for analysis of its properties such as amplitude, frequency, and time delay. The time delay in an oscilloscope refers to the interval between specific points in the waveform, such as between peaks or zero crossings.

Working Principle: Oscilloscopes work by sampling the input signal and plotting it on a screen as a function of time. The horizontal axis represents time, while the vertical axis represents the signal’s amplitude. By analyzing the waveform, one can measure various parameters, including the time delay.

Correct Option Analysis:

The correct option is:

Option 1: Measuring the time between two successive peaks of the signal.

To measure the time delay in an oscilloscope, the most straightforward and accurate method is to observe the time interval between two successive peaks of the signal. This approach utilizes the waveform's visual representation to determine the period or frequency of the signal. By identifying the time difference between consecutive peaks, one can accurately measure the time delay.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Measuring the amplitude of the signal.

This option is incorrect for measuring time delay. The amplitude of the signal refers to its strength or magnitude, not the time interval between points in the waveform. While amplitude is an important parameter, it does not provide information about the time delay.

Option 3: Counting the number of weak signals.

This option is also incorrect. Counting the number of weak signals does not relate to measuring time delay. Weak signals might refer to low amplitude portions of the waveform, but this does not help in determining the time interval between specific points in the signal.

Option 4: Measuring the decibel of the signal.

This option is incorrect as well. Decibels are a unit of measurement for the intensity of the signal, typically used in audio and sound engineering. Measuring the decibel level of the signal does not provide information about the time delay.

Conclusion:

Understanding the correct method to measure time delay in an oscilloscope is crucial for accurate signal analysis. By measuring the time between two successive peaks of the signal, one can effectively determine the time delay. Other options such as measuring amplitude, counting weak signals, or measuring decibels do not provide the necessary information for time delay measurement. Proper analysis and understanding of the waveform are essential for utilizing an oscilloscope effectively in various applications.

Explanation:

Why is shielding used in oscilloscope probes?

Definition: Shielding in oscilloscope probes refers to the use of conductive materials to encase the probe and its components to protect against external electromagnetic interference. This interference, often coming from various electronic devices and environmental factors, can adversely affect the accuracy and reliability of measurements taken by the oscilloscope.

Working Principle: Shielding works on the principle of electromagnetic compatibility (EMC). It ensures that the probe is less susceptible to external electromagnetic fields, thereby maintaining the integrity of the signal being measured. The shielding typically involves a conductive material, such as metal, which encloses the probe and acts as a barrier to electromagnetic interference.

Correct Option Analysis:

The correct option is:

Option 2: To reduce external electromagnetic interference.

This option correctly describes the primary purpose of shielding in oscilloscope probes. The shielding effectively minimizes the impact of external electromagnetic interference, ensuring that the oscilloscope provides accurate and reliable measurements.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: To control the electron beam in the oscilloscope.

This option is incorrect because shielding is not used to control the electron beam in the oscilloscope. The electron beam is controlled by the internal components of the oscilloscope, such as the electron gun and deflection plates, which direct the beam to create the visual representation of the signal on the screen.

Option 3: To increase the probe’s sensitivity.

This option is also incorrect. While shielding can help improve the accuracy of measurements by reducing interference, it does not directly increase the sensitivity of the probe. The sensitivity of an oscilloscope probe is determined by its design and the quality of its components.

Option 4: To amplify weak signals.

This option is incorrect as well. Shielding does not amplify signals. Signal amplification is typically achieved through the use of amplifiers within the oscilloscope or external amplifier circuits. Shielding is solely for the purpose of reducing interference.

The correct answer is: 4) To synchronise the input signal with the electron beam

Explanation:

A delay line in an oscilloscope temporarily holds the input signal to ensure it reaches the vertical deflection plates at the same time as the sweep generator (horizontal beam) triggers. This synchronization allows the waveform to be displayed stably and accurately from the start of the sweep.

The calibration signal usually available from a Cathode Ray Oscilloscope (CRO) is typically a square wave voltage.

This signal helps in adjusting and verifying the time base and amplitude settings of the oscilloscope.

The calibration signal available from CRO is a saw-tooth waveform. It is applied at vertical plates whereas input is applied at horizontal plates.

Option Analysis

1. Reduce noise → Delay lines don’t filter noise; they introduce a fixed time delay.

2. Enhance resolution → Resolution depends on ADC and display, not the delay line.

3. Increase amplitude → Delay lines don’t amplify signals; they preserve their shape.

Block diagram of CRO

1. The Vertical Amplifier: It block amplifies the weak signals so that they produce measurable deflection on the screen; this amplifier decides the sensitivity and bandwidth of the CRO. Its output is given as input to the delay line.
2. Horizontal amplifier: The last block is the strength of a sawtooth signal available at the output of a time-based generator is not sufficient thus before applying it to the horizontal plates the signal is amplified using a horizontal amplifier.
3. Trigger Circuit: The third block is a trigger circuit. This circuit generates trigger pulses that keep the synchronization between the input signal and the horizontal deflection circuit.
4. The time-based generator generates sawtooth waveforms and applies them between the horizontal deflection plates as the Sawtooth wave varies linearly with time and takes place at a constant velocity hence x-axis of the CRO can be calibrated in terms of time and input can be displayed with respect to time.
5. Delay line: The input signal is applied to the horizontal as well as the vertical deflection plates but before reaching the horizontal deflection plates. The signal passes through different blocks such as trigger circuit time-based generator and the horizontal amplifier thus a small delay occurs and the signal reaches the vertical deflection plates before the horizontal plates but this causes the distortion of a signal on the screen to avoid this situation a small amount of delay is added using the delay line block after the vertical amplifier.

Explanation:

In a Cathode Ray Oscilloscope (CRO), the measurement of time delay is achieved by using the time base control and measuring the horizontal shift. This method leverages the fundamental operation of the CRO, where the horizontal deflection is proportional to time, allowing for accurate time measurements of electronic signals.

Important Information:

Analyzing the other options:

1. By varying the intensity of the electron beam: This option is incorrect because varying the intensity (brightness) of the electron beam does not affect the time measurement. The intensity control adjusts the brightness of the displayed waveform but does not influence the horizontal deflection or time base settings.
2. By adjusting the brightness of the display: Similar to the first option, this method is not related to measuring time delay. Adjusting the brightness only changes how visible the waveform is on the screen and does not impact the time measurement.
3. By using the time base control and measuring the horizontal shift: This is the correct method for measuring time delay in a CRO. The time base control sets the horizontal deflection rate, and by measuring the horizontal shift of the waveform, the time delay can be accurately determined.
4. By changing the vertical deflection voltage: This option is incorrect as well. Changing the vertical deflection voltage affects the amplitude of the displayed signal but does not influence the horizontal deflection or time measurement.

In conclusion, the correct method for measuring time delay in a Cathode Ray Oscilloscope (CRO) is by using the time base control and measuring the horizontal shift, as this method directly relates to the time interval represented on the screen. The other options do not affect the time measurement and are thus not suitable for this purpose.

Concept:

CRO is a cathode-ray oscilloscope used to measure amplitude, frequencies, and phase angles of sinusoidal signals.

The display screen of the Oscilloscope is as follows:

Graticule: graticule is the grid on the display screen of an oscilloscope that comprises the horizontal and vertical axes. The graticule is used to visually measure waveform parameters.

Important points:

Focus in CRO: The electron beams entering the field at angles other than the normal to the equipotential surfaces will be deflected towards the normal and the beam is thus focused towards the center of the tube axis.

Aquadag: The aquadag coating has two functions: it maintains a uniform electric field inside the tube near the screen, so the electron beam remains collimated and is not distorted by external fields, and it collects the electrons after they have hit the screen, serving as the return path for the cathode current.

Intensity control: Intensity control is provided for adjustment of the brightness of the spot on the screen. It is accomplished by varying the voltage between the first and second anodes.

Lissajous pattern:

• The lissajous figure is the pattern that is displayed on the CRO when sinusoidal signals are applied to both horizontal & vertical deflection plates of CRO.
• The lissajous figures are used for the measurement of frequencies, and phase differences of the sinusoidal signals.
• The table of lissajous figures for different phase angles is given below:

• CRO is a very versatile instrument in the laboratory for measurement of voltage, current, frequency and phase angle of any electrical quantity.
• We cannot directly measure power by using CRO.
• The current is measured indirectly by measuring voltage drop across an impedance.
• A Lissajous figure is a pattern which is displayed on the screen when sinusoidal signals are applied to both horizontal & vertical deflection plates of CRO.
• These are used to measure the frequency of the given signals and phase difference between the signals.
• From the shape of the Lissajous pattern displayed on the CRO screen information about relative phases of signals and the frequency ratio of signals can be determined.
• It is not used for precise measurement; it depends on the type of signals.
• If one frequency is an integral multiple (harmonic) of the other, the pattern will be steady. If not, the figure will not be stationary.
   

Important Points

Common Lissajous pattern observed when two signals with different phase angle are applied to the two plates is as shown:

Cathode Ray Oscilloscope (CRO)

• A cathode ray oscilloscope (C.R.O.) is an instrument that converts electrical signals to a visual display.
• A CRO can be Used to Measure Voltage, Frequency, and Phase. It is also used to measure electrical quantities like amplitude and time period.
• The main structure of the C.R.O. is a highly evacuated cathode ray tube (C.R.T.) which emits an electron beam known as a cathode ray beam.
• The cathode ray tube consists of three main components: an electron gun, a deflection system, and a fluorescent screen.
• The electron gun is used to produce a narrow beam of electrons. 
• The deflection system allows the electron beam to be deflected from its straight-line path when it leaves the electron gun. After deflection, the speed of electrons is reduced. So, to increase the speed, the signal frequency in a CRO is kept at more than 10 MHz.
• When electrons in the beam strike the screen, the material fluoresces and becomes luminous or glows. This enables a bright spot to appear wherever an electron beam strikes the screen.
• Electrons are particles and they have mass. Since they move at high speed, they have kinetic energy.
• When these high-energy electrons strike the screen, the fluorescent coating on the screen converts the kinetic energy of the electrons into light energy.

Concept:

Analysis:

When same signal is applied to the X-Y plate of CRO a straight line with slope = 1 is observed.

On the screen (Some signal means 0° angle diffusion)

So option (d) is correct choice

More Information:

i). When 0

ii) When 90°

= 

Astigmatism: This is an additional focusing control and is analogous to astigmatism in optical lenses.

Focus Control:

In the electron gun of CRT, the middle anode is kept at lower potential concerning the other two anodes and it acts as an electrostatic lens and the focal length of these lenses can be varied by varying the potential of the middle anode concerning the other two anodes. So focusing of an electron beam is done by varying the potential of middle anode with respect the help of a potentiometer

Solution:

So Astigmatism control on the CRO panel is used for Focus Control.

Option 1 correct choice

More information:

Properties of CRO:

1. CRO can be used to measure voltage, current, frequency inductance, admittance, resistance and power factor

2. CRO can be used for the measurement of high frequency because of the constant Gain-BW product.

3. Its input impedance is very high so no loading effect occurs.

4. It has high sensitivity and accuracy.

Concept:

The CRO stands for a cathode ray oscilloscope.it consists of a set of blocks which are, shown in the following block diagram.

Subparts of Cathode Ray Tube are

• Electron gun: It emits electrons and forms them into a beam with the help of a heater, cathode, grid, and pre-accelerating, accelerating, and focusing anode.
• Vertical deflection plates: VDP is applied with a test signal. Whose waveform has to be observed on the screen VDP is kept in Horizontal position.
• Horizontal deflection plates:  HDP is used for shifting the electron beam horizontally i.e. horizontal time scale is adjusted by changing HDP potential manually.
• Screen: A standard screen size is 8 cm by 10 cm. The screen is coated with phosphor that emits light when struck by the electron beam

Hence, the Time-base generator is a part of CRO but not a part of CRT.

Uses of CRO:

• Used to measure the voltage, current, frequency, inductance, admittance, resistance, and power factor.
• used to monitor the signal properties as well as characteristics and also
• Used to control the analog signals.

Important Points

• Vertical deflection plates are mounted horizontally.
• Horizontal plates are mounted vertically as shown in the block diagram. 

Delay Circuit in CRO:

• The technique of adding a precise amount of time between the trigger point and the beginning of the scope sweep in a CRO is known as the delayed sweep.
• The input signal is not directly applied to the vertical plates because the part of the signal gets lost when the delay time is not used.
• Therefore, a delay line is placed between output of vertical amplifier and y input of cathode ray tube, to delay incoming unknown signal.
• The purpose of delay line is to synchronize unknown signal with sweep signal such that complete signal portion will be displayed without any loss.

The CRO stands for a cathode ray oscilloscope.

Subparts of the Cathode Ray Tube are:

Electron gun: 

• It emits electrons and forms them into a beam with the help of a heater, cathode, grid, and pre-accelerating, accelerating, and focusing anode.
• In the electron gun of CRT, the middle anode is kept at a lower potential than the other two anodes and it acts as an electrostatic lens the focal length of these lenses can be varied by varying the potential of the middle anode concerning the other two anodes.
• So focusing of an electron beam is done by varying the potential of the middle anode with the help of a potentiometer.

Vertical deflection plates: VDP is applied with a test signal. Whose waveform has to be observed on the screen VDP is kept in a Horizontal position.

Horizontal deflection plates:  HDP is used for shifting the electron beam horizontally i.e. horizontal time scale is adjusted by changing HDP potential manually.

Screen: A standard screen size is 8 cm by 10 cm. The screen is coated with a phosphor that emits light when struck by the electron beam

Uses of CRO:

• Used to measure the voltage, current, frequency, inductance, admittance, resistance, and power factor.
• used to monitor the signal properties as well as characteristics and also
• Used to control the analog signals.