Translations
Code | Language | Translator | Run | |
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Credits
Fu-Kwun Hwang - Dept. of Physics,National Taiwan normal Univ.; lookang
Learning Outcomes
(h) determine the frequency of sound using a calibrated c.r.o
Briefing Doc: Oscilloscope Model JavaScript HTML5 Applet Simulation Model
Source: Open Educational Resources / Open Source Physics @ Singapore
Main Themes:
- Educational Simulation: The document describes an interactive JavaScript applet that simulates the functionality of an oscilloscope, aiming to enhance student understanding of this essential electronic instrument.
- Open Educational Resources: The simulation is provided as an open educational resource, emphasizing accessibility and free usage for learners and educators.
- Physics Education: The applet is specifically targeted towards secondary level physics education, addressing topics like general waves and electromagnetic induction.
Most Important Ideas/Facts:
- Oscilloscope Basics: The simulation aims to convey the basic principles of an oscilloscope, including its core components (cathode ray tube, deflection plates, time base, amplifiers) and how they work together to display electrical signals.
- Learning Outcomes: The simulation aims to facilitate the achievement of specific learning outcomes, particularly the ability to determine the frequency of sound using a calibrated oscilloscope.
- Interactive Exploration: The applet allows students to manipulate various parameters, including time scale, horizontal offset, wave amplitude, and phase angle. This interactivity fosters active learning and exploration of different signal characteristics.
- Mathematical Representation: The document emphasizes the mathematical underpinnings of the oscilloscope's operation, providing equations that govern the horizontal and vertical deflection of the electron beam.
"The default form for this java applet is Fy(t)=A sin(w t + B)"
- Alternative Resources: The document lists additional resources, including other oscilloscope simulations and interactive tools, providing educators with a broader range of options for teaching this concept.
Quotes:
- Oscilloscope Operation: "The oscilloscope is an electronic instrument widely used in making electrical measurements. The main component of the oscilloscope is the cathode ray tube (CRT)."
- Deflection Plates: "The electrons are deflected in various directions by two sets of plate placed at right angle to each other in the neck of the tube."
- Time Base: "Signal for the horizontal deflection plate (X-axis) is generated by the scope. It mathematic form is Fx(t)= C t + D (default)."
Overall Significance:
This educational resource leverages technology to provide a visual and interactive learning experience for students grappling with the complexities of oscilloscopes. Its open nature contributes to the democratization of knowledge and offers educators a valuable tool to enrich their teaching practices.
Oscilloscope Operation and Functionality
Study Guide Review
Cathode Ray Tube (CRT)
- The core component of an oscilloscope.
- Functions as a vacuum tube where electrons are accelerated and deflected by electric fields.
- Two sets of plates, positioned perpendicularly, control the deflection of electrons.
Horizontal and Vertical Deflection
- Horizontal deflection plates (X-axis) are controlled by the oscilloscope's time base, producing a sawtooth waveform.
- The rising phase of the sawtooth moves the electron beam across the screen, while the falling phase returns it to the starting point.
- External signals being measured are applied to the vertical deflection plates (Y-axis).
Time Base and Signal Display
- The time base generates the X-axis of the Voltage/Time (V/t) graph.
- The TIME/DIV control adjusts the time base frequency, altering the X-axis scale.
- The Y-amplifier, connected to the Y-plates, provides the Y-axis of the V/t graph.
- The VOLTS/DIV control modifies the Y-amplifier gain, scaling the display size.
Triggering and Signal Stability
- The trigger circuit delays the time base to display a consistent portion of the input signal.
- This results in a stable image on the screen for easier measurement.
Axis Adjustment and Positioning
- The X-POS and Y-POS controls allow for horizontal and vertical adjustments of the signal display.
- This enables customization of the display for specific signal types like pulse waveforms.
Mathematical Representation of Signals
- The horizontal deflection signal (X-axis) can be represented as: Fx(t) = Ct + DC: Time scale
- D: Horizontal offset
- The vertical deflection signal (Y-axis) can be represented as: Fy(t) = A sin(wt + B)A: Amplitude of the wave
- B: Phase angle (in radians) of the wave from the origin
AC/DC Switch Functionality
- The AC/DC switch dictates the signal path.
- In the DC position, there's a direct connection to the Y-amplifier, allowing both AC and DC signals.
- In the AC position, a capacitor is introduced, blocking DC signals while allowing AC signals to pass.
Short Answer Quiz
Instructions: Answer the following questions in 2-3 sentences each.
- What is the purpose of the cathode ray tube (CRT) in an oscilloscope?
- How does the time base contribute to the signal display on an oscilloscope screen?
- Explain the role of the Y-amplifier in an oscilloscope.
- What is the function of the trigger circuit in an oscilloscope?
- How do the X-POS and Y-POS controls affect the signal display?
- Describe the purpose of the AC/DC switch on an oscilloscope.
- What does the variable C represent in the horizontal deflection signal equation?
- What does the variable A represent in the vertical deflection signal equation?
- Explain how a capacitor is used in the AC signal path of an oscilloscope.
- How does the oscilloscope allow for the measurement of different types of signals?
Answer Key
- The CRT is the heart of the oscilloscope. It's a vacuum tube where electrons are emitted, accelerated, and deflected to create a visible trace on the screen, representing the input signal.
- The time base generates a sawtooth waveform that controls the horizontal deflection of the electron beam. This creates the X-axis of the V/t graph, allowing us to see the signal's variation over time.
- The Y-amplifier amplifies the input signal and applies it to the vertical deflection plates. This controls the vertical movement of the electron beam, forming the Y-axis of the V/t graph, representing the signal's amplitude.
- The trigger circuit ensures a stable display by synchronizing the horizontal sweep with the input signal. This prevents the waveform from appearing to drift across the screen, making measurements much more accurate.
- The X-POS and Y-POS controls allow you to shift the displayed waveform horizontally and vertically, respectively. This is useful for positioning the signal optimally on the screen for better visualization and analysis.
- The AC/DC switch lets you choose whether to view only the AC component, the DC component, or both of the input signal. In the AC position, a capacitor blocks the DC component, letting you focus on the AC variations.
- The variable C in the horizontal deflection signal equation, Fx(t) = Ct + D, represents the time scale. It determines how fast the electron beam sweeps across the screen, influencing the horizontal spread of the displayed waveform.
- The variable A in the vertical deflection signal equation, Fy(t) = A sin(wt + B), represents the amplitude of the wave being measured. It governs the vertical height of the waveform displayed on the oscilloscope screen.
- In the AC position of the switch, a capacitor is placed in series with the input signal. Since capacitors block DC current but allow AC current to pass, this effectively filters out any DC component of the input, allowing only the AC part to reach the Y-amplifier.
- By adjusting the time base (TIME/DIV) and the vertical sensitivity (VOLTS/DIV), the oscilloscope can accommodate signals with different frequencies and amplitudes, enabling the visualization and measurement of a wide range of electrical phenomena.
Essay Questions
- Explain in detail the process of how an electron beam is generated, accelerated, and deflected within the CRT of an oscilloscope.
- Discuss the importance of the time base in displaying a stable waveform on an oscilloscope screen. What happens if the time base is not synchronized with the input signal?
- Compare and contrast the functions and applications of the AC and DC settings on an oscilloscope's input switch. Provide examples of scenarios where each setting would be preferred.
- Analyze the mathematical representations of the horizontal and vertical deflection signals in an oscilloscope. How do the variables in these equations influence the appearance of the displayed waveform?
- Describe how an oscilloscope can be used to measure the frequency and amplitude of a sinusoidal waveform. Include a discussion of the relevant controls and settings on the oscilloscope and how they are used to obtain these measurements.
Glossary
TermDefinitionAnodeA positively charged electrode that attracts electrons.CathodeA negatively charged electrode that emits electrons.Cathode Ray Tube (CRT)A vacuum tube that uses an electron beam to create images on a phosphorescent screen.Deflection PlatesPairs of electrodes within a CRT that control the direction of the electron beam.Electron BeamA stream of electrons emitted from a cathode and focused by anodes.FrequencyThe number of cycles per second of a periodic waveform, measured in Hertz (Hz).OscilloscopeAn electronic instrument used to visualize and measure electrical signals.Phase AngleThe angular displacement of a sinusoidal waveform from a reference point, often measured in radians or degrees.Phosphorescent ScreenA screen coated with a material that emits light when struck by electrons.Sawtooth WaveformA periodic waveform characterized by a linear ramp up followed by a rapid drop.Time BaseThe circuitry within an oscilloscope that generates the sawtooth waveform used for horizontal deflection.Trigger CircuitThe circuitry that synchronizes the horizontal sweep with the input signal to create a stable display.Vacuum TubeA sealed glass tube with most of the air removed, allowing for the free flow of electrons.Voltage/Time (V/t) GraphA graphical representation of an electrical signal's voltage over time.Y-AmplifierAn amplifier that increases the amplitude of the input signal before applying it to the vertical deflection plates.
Theory
Like a televison screen, the screen of an oscilloscope consists of a cathode ray tube. Although the size and shape are different, the operating principle is the same. Inside the tube is a vacuum. The electron beam emitted by the heated cathode at the rear end of the tube is accelerated and focused by one or more anodes, and strikes the front of the tube, producing a bright spot on the phosphorescent screen.
The electron beam is bent, or deflected, by voltages applied to two sets of plates fixed in the tube. The horizontal deflection plates, or X-plates produce side to side movement. As you can see, they are linked to a system block called the time base. This produces a sawtooth waveform. During the rising phase of the sawtooth, the spot is driven at a uniform rate from left to right across the front of the screen. During the falling phase, the electron beam returns rapidly from right ot left, but the spot is 'blanked out' so that nothing appears on the screen.
In this way, the time base generates the X-axis of the V/t graph.
The slope of the rising phase varies with the frequency of the sawtooth and can be adjusted, using the TIME/DIV control, to change the scale of the X-axis. Dividing the oscilloscope screen into squares allows the horizontal scale to be expressed in seconds, milliseconds or microseconds per division (s/DIV, ms/DIV, µs/DIV). Alternatively, if the squares are 1 cm apart, the scale may be given as s/cm, ms/cm or µs/cm.
The signal to be displayed is connected to the input. The AC/DC switch is usually kept in the DC position (switch closed) so that there is a direct connection to the Y-amplifier. In the AC position (switch open) a capacitor is placed in the signal path. As will be explained in Chapter 5, the capacitor blocks DC signals but allows AC signals to pass.
The Y-amplifier is linked in turn to a pair of Y-plates so that it provides the Y-axis of the the V/t graph. The overall gain of the Y-amplifier can be adjusted, using the VOLTS/DIV control, so that the resulting display is neither too small or too large, but fits the screen and can be seen clearly. The vertical scale is usually given in V/DIV or mV/DIV.
The trigger circuit is used to delay the time base waveform so that the same section of the input signal is displayed on the screen each time the spot moves across. The effect of this is to give a stable picture on the oscilloscope screen, making it easier to measure and interpret the signal.
Changing the scales of the X-axis and Y-axis allows many different signals to be displayed. Sometimes, it is also useful to be able to change the positions of the axes. This is possible using the X-POS and Y-POS controls. For example, with no signal applied, the normal trace is a straight line across the centre of the screen. Adjusting Y-POS allows the zero level on the Y-axis to be changed, moving the whole trace up or down on the screen to give an effective display of signals like pulse waveforms which do not alternate between positive and negative values.
The above information are quoted from http://www.doctronics.co.uk/scope.htm
This applet simulate how the socilloscope works (This is an EJS version of the [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=34.msg207#msg207]oscilloscope[/url] applet).
The oscilloscope is an electronic instrument widely used in making electrical measurements.
The main component of the oscilloscope is the cathode ray tube (CRT).
The CRT is a vacuum tube in which electrons are accelerated and deflected under the influence of electric field. The electrons are deflected in various directions by two sets of plate placed at right angle to each other in the neck of the tube.
Signal for the horizontal deflection plate (X-axis) is generated by the scope
It mathematic form is Fx(t)= C t + D (default)
C : time scale
D : horizontal offset
The external signal (need to be measured) is applied to the vertical deflection plate (Y axis).
The default form for this java applet is Fy(t)=A sin(w t + B)
A : amplitude of the wave
B : phase angle in radian of the wave from the origin (0,0), the control is in degrees while the formula is expressed in radians
You can change X or Y axis signal to either kind of signal.
Video
https://notebooklm.google.com/notebook/dc8700ac-97ba-4fec-b9ee-3c97c06eb560/audio
Versions
- http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=2166.0 EJS version of oscilloscope by Fu-Kwun Hwang
Other Resources
- https://academo.org/demos/virtual-oscilloscope/ suggested by Issac
- https://www.geogebra.org/m/e87sbuy8 by seng kwang
Oscilloscope FAQ
What is an oscilloscope?
An oscilloscope is an electronic instrument used to measure and visualize electrical signals. It displays the voltage of a signal over time, allowing you to observe the shape, frequency, amplitude, and other characteristics of the signal.
How does an oscilloscope work?
An oscilloscope uses a cathode ray tube (CRT) to display the signal. A beam of electrons is emitted from a heated cathode and accelerated towards a phosphorescent screen. Two sets of plates, the X-plates and Y-plates, control the deflection of the electron beam.
- X-plates (Time Base): These plates control the horizontal movement of the electron beam. They are connected to a time base circuit that generates a sawtooth waveform, causing the beam to sweep across the screen from left to right at a constant speed. This creates the time axis on the display.
- Y-plates (Signal Input): The signal to be measured is connected to the Y-plates. The voltage of the signal controls the vertical deflection of the electron beam, creating the voltage axis on the display.
The combined action of the X-plates and Y-plates results in a visual representation of the signal's voltage over time on the screen.
What are the main controls on an oscilloscope?
- TIME/DIV: Adjusts the time scale of the horizontal axis, controlling how much time is represented by each division on the screen.
- VOLTS/DIV: Adjusts the voltage scale of the vertical axis, controlling how much voltage is represented by each division on the screen.
- AC/DC Switch: Selects whether the input signal is coupled directly (DC) or through a capacitor (AC), which blocks DC components of the signal.
- Trigger: Controls when the oscilloscope starts displaying the signal. This is essential for stabilizing the display of repetitive signals.
- X-POS and Y-POS: Adjust the horizontal and vertical position of the trace on the screen.
How is the frequency of a signal determined using an oscilloscope?
The frequency of a repetitive signal can be determined by measuring the period of the waveform displayed on the oscilloscope. The period is the time it takes for one complete cycle of the waveform. The frequency is the reciprocal of the period (f = 1/T).
To measure the period, use the TIME/DIV control to adjust the time scale until one or more complete cycles are visible on the screen. Then measure the number of horizontal divisions occupied by one cycle and multiply that by the time per division setting.
What is the purpose of the trigger circuit?
The trigger circuit ensures that the oscilloscope displays a stable image of the input signal. It delays the start of the time base sweep until a specific point on the input signal is detected, ensuring that the same portion of the waveform is displayed each time the sweep occurs. This is particularly important for observing repetitive signals.
What are some common applications of oscilloscopes?
- Electronics: Troubleshooting circuits, testing components, analyzing signal waveforms, measuring voltage and frequency.
- Telecommunications: Testing and analyzing communication signals.
- Automotive: Diagnosing engine problems, analyzing sensor data.
- Medical: Monitoring heartbeats, brain waves, and other physiological signals.
What are the advantages of using an oscilloscope simulation?
- Accessibility: Simulations make oscilloscopes accessible to anyone with a computer or mobile device.
- Safety: Simulations eliminate the risks associated with working with high voltages in real circuits.
- Cost-effectiveness: Simulations are often free or low-cost compared to purchasing and maintaining physical oscilloscopes.
- Experimentation: Simulations allow users to experiment with different signal types and oscilloscope settings without the limitations of real equipment.
What are the limitations of an oscilloscope simulation?
While simulations provide a valuable learning tool, they cannot fully replicate the experience of using a real oscilloscope. Some limitations include:
- Real-world variations: Simulations may not accurately model all the nuances and imperfections found in real-world signals and circuits.
- Limited functionality: Some simulations may lack advanced features found in high-end physical oscilloscopes.
- Hardware interaction: Simulations cannot replace the hands-on experience of connecting probes and interacting with physical equipment.
- Details
- Parent Category: 05 Electricity and Magnetism
- Category: 09 Electromagnetic Induction
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