The general block diagram of CRO is shown below. It usually consists of the major blocks namely:
The Vertical Amplifier 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.
Delay line block the next block is the delay line we know that 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.
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.
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.
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
Fig 2 : Block Diagram of CRO
A CRO (Cathode Ray Oscilloscope) works by using a high- speed electron beam that is deflected by an electric or magnetic field to produce a visual display of an electrical signal. When the electrical signal is applied to the two deflection plates to produce electric fields perpendicular to each other. The electron beam is deflected by these fields, causing it to hit a phosphorescent screen, producing a bright spot. The position of the spot on the screen represents the magnitude and waveform of the electrical signal. By measuring the position of the spot, the frequency, amplitude, and waveform of the signal can be determined.
Fig 3 : Cathode Ray Oscilloscope diagram
The (CRO) Cathode Ray Oscilloscope consists of the following components:
Cathode Ray Tube
The primary purpose of the CRT, a vacuum tube, is to convert electrical signals into visual signals. The electrostatic deflection plates and electron gun are also a part of this tube. This electron gun's primary use is to produce a focussed electrical ray with a high frequency.
The horizontal ray transfers the electron beams from the left to the right, whereas the vertical deflection plate shifts the ray up and down. The beam can be found anywhere on the monitor because all these acts are independent of one another.
Electron Gun Assembly
The electron gun's primary purpose is to emit electrons so they can be transformed into rays. A heater, a grid, a cathode, and anodes are for accelerating, pre-accelerating, and focussing the major components of this gun. Strontium and barium layers are formed at the cathode end to achieve high electron emission at a reasonable temperature. Barium layers are deposited at the cathode end.
Once the cathode grid has generated the electrons, they flow through a centrally located co-axial through the CRT's axis and into the control grid, which is often a nickel cylinder. Therefore, it regulates the cathode's ability to create strong electrons.
Deflecting plate
The electron ray will pass through both sets of the deflecting plates when it leaves the electron gun. This arrangement will produce on the vertical deflecting plate known as the Y plate's vertical deflection. The horizontal deflection, often known as the X plate's generally horizontal deflection, is done using the other set of the plate.
Fluorescent Screen
The faceplate, or front face, of a CRT monitor, is flat and is around 100 mm by 100 mm in size. For larger screens, the CRT screen is slightly curved, and the faceplate can be created by pushing the molten glass into a mold and then heating it.
Phosphor crystals are used to cover the inside face of the faceplate and convert electrical energy into light. This phenomenon is known as fluorescence it occurs when an electronic ray strikes the phosphor crystal, increasing its energy level and causing light to be produced during the crystallization of phosphorous.
Glass Envelope
It is a very evacuated conical kind of structure. The aquadag covers the inside faces of the CRT located between the neck and the display. This substance conducts electricity and functions as a high-voltage electrode. In order to assist the electron in serving the center, the coating's surface is electrically attached to the accelerating anode.
The CRO may be used to measure electrical quantities like amplitude, time period, and frequency.
The CRO is used to measure various electrical quantities such as voltage, current, and frequency. The electron beam is directed at a phosphor-coated screen to produce a visual representation of the electrical signal. To measure a specific electrical quantity, the CRO is connected in parallel or series with the circuit under test and the voltage or current waveform is displayed on the screen. By analyzing the waveform, the CRO can provide accurate readings of various electrical quantities such as peak voltage, frequency, and duty cycle
Fig 4 : Analyzing the waveform of CRO
The voltage signal is displayed on the screen as if it was a time function. The signal's amplitude is consistent, but using the volt/division button on top of the CRO board, we can adjust how many divisions are used to conceal the voltage signal in a vertical direction. So, using the method below, we can measure the signal's amplitude as it appears on the CRO screen.
A = Amplitude of the signal
j = is the volt/division value
nv = no. of partitions that cover the displayed signal in vertical axis
\(voltage= distance \space in \space cm \times volts/cm\)
Fig 5 : Measurement of Voltage
On its screen, CRO shows the voltage signal as a function of time. The time duration of that periodic voltage signal is fixed, but by adjusting the time/division knob on the CRO panel, we may change the number of divisions that span one full cycle of the voltage signal in the horizontal direction. Therefore, by applying the following formula, we will be able to determine the Time duration of the signal that is visible on the CRO screen. The time taken for the signal to complete one cycle is called time duration
T = time period of the signal
j = is the time/division value
Nv = no. of partitions that cover up one whole cycle of the periodic signal on horizontal axis
\(1ms = 0.001 s \space and \space1\mu s=0.000001s\)
Fig 6: Measurement of Time
The horizontal scale on the CRO screen makes it very simple to measure time and frequency. The size of the signal on your CRO display should be increased if you want to ensure precision while measuring a frequency so that the waveform can be converted more easily. Initially, the time can be determined by counting the number of flat partitions from one end of the signal to the other whenever it passes the flat line and using the horizontal scale on the CRO. The signal's time period can then be determined by increasing the number of flat segments through time or division.\(Frequency = \frac\)
Fig 7: Measurement of Frequency
Position, brightness, focus, astigmatism, blanking, and calibration are the primary controls of a CRO (Cathode Ray Oscilloscope).
Position
The position control knob on an oscilloscope is mostly used to move the intense point from the left to the right. One can easily move the place from the left side to the right side by using the knob.
Brightness
The electron's intensity has a significant impact on the ray's brightness. The electron ray's electron intensity is determined by the control grids. As a result, the brightness of the electron rays can be changed and adjusted accordingly to control the grid voltage.
Fig 8 : Controls of CRO
Focus
By adjusting the applied voltage to the CRO's center anode, the focus can be controlled. The electrostatic lens can be created using the center and additional anodes nearby. As a result, by adjusting the voltage across the center anode, the main length of the lens can be altered.
Astigmatism and Blanking circuit
The CRO oscilloscope's time base generator produced the blanking voltage. This additional focusing control in CRO is comparable to astigmatism in optical lenses. Due to the different lengths of the electron pathways at the center and the corners of the screen, a beam that is focussed in the monitor's middle would be defocused here. The oscilloscope's time base generator produced the blanking voltage.
Calibration circuit
In order to calibrate an oscilloscope, an oscillator is required. The oscillator, however, should produce a square waveform for a predetermined voltage.
Graticule
It is the grid on the display screen of the CRO that consists of the horizontal and vertical axis.
Input impedance
The input impedance is greater than 1 Megaohms, a high value of impedance is used to prevent the circuit from the scope from being tested. To match fast amplifiers and other devices.
Trigger level and slope
It's for the adjustment of voltage and an AC power line triggers the slope at a frequency of 50 Hz.
AC/GND/DC Switch
In general the DC switch is used for all other signals including AC.
Now that we have learnt about the CRO in detail let us take a look at its advantages and disadvantages.
many terminals for device control.
The CRO can be utilized in the lab as
This article summarises all the information related to CRO(Cathode Ray Oscilloscope), which helps in your preparation for various AE/JE examinations. To boost up your preparation, you can test yourself through a series of Mock Tests for Electrical Engineering Exams. You can also check the syllabus for the AE/JE exam. You can also visit the Testbook app to keep yourself updated with all the exam-oriented information and concepts related to the upcoming examinations, including Electrical Gate Exam and SSC JE and RRB JE
CRO full form is Cathode Ray Oscilloscope, is a very fast X-Y plotter that can display an input signal versus time or another signal.An electrical test device called a cathode ray oscilloscope is used to produce waveforms in response to several input signals. It was originally known as an oscillograph.
The heater of the electron gun generates the electron beam using low voltage. The cathode ray tube needs a high voltage to accelerate the beam. Other oscilloscope control units require the standard voltage supply. In between electron gun and the screen are placed between the horizontal and vertical plates, allowing it to detect the beam in accordance with the input signal, and display it on the screen.
The CRO oscilloscope's time base generator produces the blanking voltage. This additional focusing control in CRO is comparable to astigmatism in optical lenses. Due to the different lengths of the electron pathways at the center and the corners of the screen, a beam that is focused in the monitor's middle would be defocused here
Phosphor crystals are used to cover the inside face of the faceplate and convert electrical energy into light. This phenomenon is known as fluorescence it occurs when an electronic ray strikes the phosphor crystal.
