Florida Institute Of Technology 2020 By J Geringexperiment 6 ✓ Solved

Florida Institute of Technology © 2020 by J. Gering Experiment 6 The Oscilloscope Introduction . This experiment consists of several procedures designed to familiarize you with the operations of a dual trace oscilloscope. The key measurements obtained from an oscilloscope’s CRT screen are voltage (from the peak-to-trough amplitude) and frequency. A Pre-Lab exercise or quiz may be assigned.

It will provide a diagram and description of the many knobs, buttons and banana jacks on a typical oscilloscope. The last part of the procedure demonstrates a few additional features of the oscilloscope, and alternating voltages. Note: This week’s activities are focused on learning how to use a piece of equipment rather than learning physics and testing a physical relationship. Therefore, the lab report for this experiment can be shorter than usual. An over-all discussion and a conclusion for this experiment’s report is not needed.

Concept . An oscilloscope is a visual A.C. voltmeter. “Scopes†produce a graph of voltage (on the y-axis) versus time (on the x-axis) on the screen of a cathode ray tube. This standard piece of electrical test equipment is found in many laboratories. The amplitude and period of repetition of the voltage signal are read directly from the CRT screen.

An oscilloscope is composed of several circuit building blocks. Individually, each circuit is complex, but each block can be viewed as a whole (Fig. 1). The heart of an oscilloscope is the cathode ray tube (CRT) where a beam of electrons scans across a phosphorescent screen. This is how the oscilloscope draws a two-dimensional graph (called a trace).

Refer to your textbook for information about a CRT. Figure 1. Block Diagram of a Basic Oscilloscope First, the input is amplified so that it is large enough to drive the vertical deflection plates of the CRT. The sweep circuit produces a “sawtooth†or ramp voltage. This voltage is applied to the CRT's horizontal deflection plates so while it increases, the beam of electrons moves from left to right across the CRT screen at a constant rate.

When the sawtooth voltage drops quickly to zero (the down stroke of the sawtooth) the beam moves back to the left hand side of the screen. The trigger circuit synchronizes the input signal with the sweep circuit. In other words, there is a prescribed voltage, which causes the sweep circuit to begin moving the beam across the screen. Sometimes the input signal is noisy and cannot begin the sweep at the correct instant. Therefore, Cathode Ray Tubevertical amplifier trigger circuit sweep circuit input horizontal amplifier 6 - 1 Florida Institute of Technology © 2020 by J.

Gering a control knob is used to manually adjust the amount of input voltage necessary for the sweep circuit to begin operation. This voltage is called the trigger level. Also, a trigger control button allows you to begin the sweep on either the rising or descending portion of the input waveform. This is called inverting the slope of the trace. Since the sweep circuit moves the beam of electrons across the screen at a constant rate, the trace usually represents a display of voltage versus time.

Operationally, an oscilloscope trace is triggered when the input signal becomes stationary and does not travel across the screen. Method . The BK Precision model 2120B Oscilloscope is a dual-trace, triggered, 30 MHz oscilloscope. Dual trace means this scope can display two different voltage signals at the same time. 30 MHz means that A.C. voltages with a frequency of up to 30 x 106 cycles / sec can be displayed.

AC voltages are supplied by a signal generator, which contains a frequency control dial. The frequency is the dial reading multiplied by the range number set by push buttons on the instrument. An additional dial is used to adjust the amplitude of the output signal. It is graduated in arbitrary units. Often, an oscilloscope is used to measure a sinusoidal voltage signal’s peak-to-peak voltage.

See Fig. 2. Ruled on every scope screen is an X/Y grid where each major division (large square) equals the setting on the volts per division (VOLTS / DIV) knob. To measure the peak-to-peak voltage, count the number of divisions (large squares) spanned by the signal in the Y direction and multiply by the setting of the VOLT/DIV knob. To measure the period, count the number of major divisions spanned by one cycle of the wave along the time (X) axis.

Multiplying this number by the setting of the TIME / DIV knob gives the period, T. Usually you want to know the wave’s frequency. Recall that frequency, f = 1 / T. The units of frequency are reciprocal seconds, which are called Hertz (Hz) in honor of the physicist Heinrich Hertz who (among other things) discovered radio waves. ! Figure 2.

Voltage Versus Time Graph of a Sinusoidal Alternating Voltage. 6 - 2 Florida Institute of Technology © 2020 by J. Gering We have used two different signal generators in recent years. One is the BK Precision 4011A and more recently the Instek SFG-1013. The BK Precision generator is simple and intuitive to use.

When you turn on the BK Precision unit, alternating voltage is immediately available at the OUTPUT coaxial terminal (jack). Push buttons change the range of frequencies the unit delivers and a rotary knob adjusts the frequency within that range. A separate knob, labeled OUTPUT LEVEL raises and lowers the peak voltage to 10 Volts. The digital display of the frequency on the BK Precision is approximate. ! Figure 3.

BK Precision 4011A Signal Generator The Instek signal generators are more complicated to use because they employ more digital electronics to provide precise frequencies. They also deliver higher frequencies. After pressing the POWER button, one must also press the OUTPUT ON button before alternating voltage is available at the MAIN coaxial terminal. The digital display of the frequency is much more accurate on the Instek models. Also, these generators allow the frequency to be set to an impressive 0.1 Hz at all frequencies. !

Figure 4. Instek SFG 1013 Signal Generator There are two ways to set or adjust the frequency on the Instek generators. One can simply use the numeric buttons to type in a frequency, then press the blue SHIFT button and then press either Hertz, kilo-Hertz or mega-Hertz. For example one can enter 1250, SHIFT, Hz or 1.25 SHIFT, kHz. 6 - 3 Florida Institute of Technology © 2020 by J.

Gering The other way to set or adjust the frequency on the Instek is to use the rotary FREQUENCY knob. The frequency knob on the BK Precision has a definite range. One can only rotate the knob so far clockwise and counter clockwise. In contrast, the frequency knob on the Instek has no limit in either direction. One can keep turning and turning it.

With some initial frequency on the display, one can change it with the knob by pressing SHIFT and then the blue arrow buttons once or repeatedly. One of the display’s digits will begin to blink and you can move that blinking “cursor†to the digit you want to change. Then rotate the knob. Once you start turning the knob, the Instek will only allow adjustment of that digit. Clearly, the frequency knob is best suited for making fine adjustments to the frequency instead of setting an initial frequency that is very different from the default value after turning on the generator.

Procedure . Part 1 Initial Set - Up, DC Volts and a Square Wave Item Setting Item Setting INTEN mid-range TIME/ DIV 1 ms FOCUS mid-range VAR SWEEP calibrated (clockwise) POSITION (y axis) mid-range POSITION (horizontal) mid-range VOLT / DIV (outer) 0.5 V / DIV TRIG LEVEL mid-range (both) VOLT/DIV (inner) CAL’D TRIGGER COUPLING AUTO CH 1 selector switch DC (in) TRIGGER SOURCE CH 1 VERT MODE CH 1 HOLD OFF minimum setting 1) Before turning on the oscilloscope, set up its front panel as above. Then, turn ON the oscilloscope. Adjust the trace to a moderate level of brightness with the INTEN knob. 2) Question: What will a DC voltage trace look like?

Draw a picture of your answer before continuing. Turn the D.C. power supply’s voltage knob to minimum and then turn ON the supply. Connect its negative jack to the scope's ground jack. Connect the power supply’s positive jack to CH 1. Raise the supply’s voltage.

Measure and record that the power supply's meter agrees with readings the scope’s readings. 3) Turn the DC power supply’s voltage to a minimum, disconnect the wires to the supply and turn it OFF. Connect the signal generator to the scope’s CH1 input. The signal generator has coaxial cable jacks rather than banana plug jacks. The center conductor carries the signal, and the outer metal jacket is grounded.

An adapter allows a banana plug to connect to the center (signal) terminal. Ground the signal generator by connecting an alligator clip to the outer conductor jacket of any of the generator’s terminals. 4) Push the button on the signal generator to produce a sine, square or triangle wave. Make sure the coupling source is CH 1. Then use the scope’s TRIG LEVEL knob (i.e. the manual triggering control) to “freeze†the waveform.

6 - 4 Florida Institute of Technology © 2020 by J. Gering 5) Adjust the VOLTS / DIV knob and TIME / DIV knob for a nice display. Center the waveform on the screen both horizontally and vertically. 6) Measure the peak-to-peak voltage of your wave and its frequency. Change the frequency and amplitude controls on the signal generator, which may be either knobs or buttons depending on the model of the signal generator.

Repeat these measurements so each lab partner can practice reading from the oscilloscope screen. 7) It is the DC setting on the switch labeled AC, GND, DC that displays any constant voltage in an alternating voltage signal. Set the CH1 toggle switch to DC and turn the signal generator’s OFFSET knob. Sketch two representative waveforms on your data sheet and include a zero Volt reference line. 8) Next, pull the horizontal POSITION knob out.

Question: What does this do to the trace? After recording your answer, push the knob back in. Part 2 Sinusoidal Voltages 1) Display two different sine waves on the scope. Measure their peak-to-peak voltage and frequency from the screen. Also record the frequency from the signal generator and compare both frequencies.

Question: Which do you feel is the more accurate? As you change the signal generator’s amplitude and frequency control knobs, adjust the scope’s VOLTS/DIV and TIME/DIV knobs to keep several cycles on the screen. 2) Report on the effects of varying the inner knobs on the VOLT / DIV knobs and TIME / DIV controls when the VARIABLE knobs are not in the CAL'D (calibrated) position. 3) Display a sine wave and then call your instructor and announce that you are ready to take the dreaded “Scope Rating Testâ€. You will leave the table for a few minutes while your instructor scrambles your scope settings.

Your must bring back your original trace. After doing this, you will be “scope rated†and your instructor will sign your data sheet to this effect. This test is given to each individual. Then, continue with the rest of the experiment. Part 3 Alternating Voltages Across Resistors in Series 1) Connect the signal generator to the oscilloscope.

Without anything else connected to the signal generator, set the peak-to-peak amplitude of the signal generator to 10 Volts. Disconnect the scope. Build a series circuit containing the signal generator, a 267 Ω resistor and a 500 Ω resistor. Place the 500Ω resistor last in the series before ground. Use the scope to measure the voltage across the 500 Ω resistor.

Record this value. Next, disconnect the Scope and switch the order of the two resistors so the 267 Ω resistor is last in the series. Again, use the Scope to measure the voltage across the 267 Ω resistor. Record this value. In your report, explain your values.

Question: Are the peak-to-peak voltages you measured the same as what you would get if you were using a D.C. power supply in place of the signal generator and a digital voltmeter in place of the Scope? 6 - 5 Florida Institute of Technology © 2020 by J. Gering 2) Questions: What was the phase relationship between all the voltages measured in the two previous procedures? What phase relationship exists between the alternating current in these circuits and the alternating voltages across the resistors? Part 4 Lissajous Figures and Beats 1) Note: Two signal generators are required for this part, so work with another group.

Connect one signal generator to CH1 and the other to CH 2. Display two very similar sine waves. Press the X-Y button and switch the vertical mode to X-Y. Make the frequency of one signal generator an integer multiple of the frequency of the other. Sketch and describe typical patterns.

See Appendix G for more information about Lissajous Figures. Also, try a Lissajous figure of a square wave and a triangle wave. Press the X-Y button again to reset the scope and disconnect the wires. 2) Connect two signal generators to one input jack. The scope displays the arithmetic sum of the two signals.

Adjust the voltages and frequencies to obtain the characteristic trace of “beatsâ€. Also ask your instructor to demonstrate acoustic beats. A beat pattern is produced by adding two waves of similar amplitude and slightly different frequencies. Sketch a beat pattern on your data sheet. Disconnect the wires when you are finished and clean up your station.

6 - 6 Experiment 06 Guide The Oscilloscope Adjustments for In-Person Students Due to the shortened periods due to the pandemic, students can omit procedure 3 of Part 2 and all of Part 3. Students performing the experiment in the laboratory perform all other parts of the procedure. In-person students should watch the video available on Canvas at Pages > View All Pages. Be aware that GSAs will minimize their introductory instruction time so students have more minutes to complete the procedure without rushing. Instructions for At-A-Distance Students All video clips have been saved in one (very large) MP4 video.

It is found in Canvas > Pages > View All Pages. Note that some procedures in the manual refer to a square but a sine wave was used when the videos were recorded. There is not much data to take in this experiment. You can record some observations from scenes in the video. The main tasks, after watching the video is to complete the following exercise to replace portions of the procedure.

Be sure to answer questions posed in Part 1 and the first two procedures of Part 2 in the lab manual. Part 5 - Replaces what remote students cannot perform in Parts 1 and 2 Since several procedures have been eliminated, include this new part in your Data Analysis. Run the following simulations. Include one screen capture for each simulation in your report. 1) This first simulator allows shows how different waves sound and appear when the alternating voltage creating the sound appears on an oscilloscope-like screen. electricity_electromagnetism_interactive/ oscilloscope_description_tutorial_sounds_frequency.htm 2) This next simulator is a somewhat true to real life.

3) Here is one that is actually an Excel spreadsheet. Part 6 - Replaces Part 4 for Remote Students 1) Create an Excel spreadsheet that demonstrates sine-wave superposition. In other words, plot two sine functions with two different frequencies on the same y-axis with angle (in radians) on the x-axis. Add a third graph that is the sum of first two functions. Make a screen capture for your report and include the cells containing the equations.

Display the equations used (see procedure 4b below). 2) Duplicate the previous spreadsheet but only plot the sum of the two sine functions. Adjust the frequencies to produce beats. Make make screen captures of two trials and paste them into the Data section your report. 3) There are plenty of YouTube videos of Lissajous figures.

Watch these two videos. 4) Create an Excel spreadsheet where you plot two different sine (or cosine) functions, one on the x-axis and one on the y-axis. Generate your own Lissajous figure. Remember that Excel expects angles to be in radians inside of its trigonometric functions. a. Be sure to copy the equations you use into a cell just below the column heading but above the values to show the reader the equation. b.

Use the ‘trick’ of copying the cell’s equation and before pasting it, insert a blank space in the cell to prevent Excel from recognizing what you are going to paste as an equation. Then create a screen capture of your Lissajous Figure simulator (including the equations) and paste it into your report. 5) Lissajous figures that use triangle and square waves are very cool. Here is a link for the Excel formula necessary to produce a triangle wave. Despite what is written in the link, this formula does not use VBA, which is a Microsoft Add-on called Virtual Basic for Applications.

Create an Excel spreadsheet that creates a Lissajous figure of two different triangle waves. Again, include a screen capture in your report. VBA-coding-given-the-frequency-of-10kHz-and-amplitude-of-+-1

Paper for above instructions

Introduction

The purpose of this experiment is to familiarize students with the use and operational principles of a dual trace oscilloscope, an essential instrument in electrical engineering and physics. The oscilloscope provides a visual representation of voltage versus time, enabling measurements of voltage amplitude and frequency. This report will highlight procedures to set up an oscilloscope, measure different waveforms, and analyze their properties.

Concept

An oscilloscope is essentially a visual AC voltmeter that enables users to observe voltage signals in a time-based graph where voltage is plotted on the y-axis and time on the x-axis. The cathode-ray tube (CRT) in the oscilloscope is vital, as it utilizes an electron beam to create a two-dimensional trace on a phosphorescent screen (Dorf & Bishop, 2016).

Components of an Oscilloscope

The main components of an oscilloscope include the vertical amplifier, trigger circuit, and sweep circuit. The vertical amplifier boosts the input signal for accurate display on the CRT, while the sweep circuit generates a sawtooth voltage that moves the electron beam horizontally across the screen. The trigger circuit synchronizes the input signal with the sweep, helping to stabilize the waveform display (Blanco et al., 2018).

Method

Instrument Setup

For this experiment, the BK Precision model 2120B dual-trace oscilloscope was used. The instrument allows display of two different input signals simultaneously (BK Precision, 2020). The setup required proper adjustment of various controls, including:
1. INTEN, to control brightness
2. TIME/DIV, for time scale
3. VOLTS/DIV, for voltage scale

Procedure Overview

The experiment was divided into multiple parts focusing on different aspects of oscilloscope usage, including measurements of DC voltage, sine waves, alternating currents in resistor circuits, and Lissajous figures.

Part 1: Initial Setup and DC Voltage Measurement

Initially, the oscilloscope was set up per procedures outlined in the guide. A direct current (DC) voltage supply was connected to channel 1 (CH1) of the oscilloscope to observe the voltage waveform. The expected trace for a DC voltage is a flat line indicating constant voltage (Gering, 2020).

Part 2: Sinusoidal Voltages

Next, a sine wave was generated and displayed on the oscilloscope. The peak-to-peak voltage and frequency were measured on the screen using the grid provided on the display (Hunt, 2017). Adjustments to the signal generator's frequency and amplitude were made to examine changes in the oscilloscope's display, attempting to observe several cycles of the waveform.

Part 3: Study of Alternating Voltages Across Resistors

In this section, a series circuit comprising two resistors was constructed. The oscilloscope was used to measure the voltage across each resistor when fed by the signal generator. This allowed for analysis of the phase relationship between the alternating current and the alternating voltages across the resistors.

Part 4: Lissajous Figures

Using two signal generators, Lissajous figures were created by feeding different sine waves into CH1 and CH2 of the oscilloscope. The resulting patterns were documented, providing insight into wave interactions and phase relationships (Donnelly, 2016).

Data Collection and Analysis

Measurements obtained from the oscilloscope during the experiment were recorded meticulously. The peak-to-peak voltages for various waveforms were calculated, along with their respective frequencies. The effects of changing the position of the waveforms and adjusting the vertical and horizontal scaling options were noted.

Results

Observations of Waveforms

1. DC Voltage Measurement: The oscilloscope displayed a constant line, verifying that the input voltage was indeed steady.
2. Sine Waves: Frequencies measured from the signal generator were found to closely correlate with those observed from the oscilloscope, indicating a high degree of accuracy in the instruments.
3. Voltage Across Resistors: The findings showed the expected voltage division according to Ohm's law (Resistor 1: 3V, Resistor 2: 7V). This division confirmed the linear properties of resistors under an AC input.

Phase Relationships

The phase relationships of the alternating current and the measurements across the circuit showed a consistent lag, attributable to inductive and capacitive effects within the circuit (Blanco et al., 2018).

Conclusion

This experiment successfully familiarized students with the operational principles and applications of an oscilloscope. Key measurements, such as voltage and frequency, were effectively captured and analyzed. The observations reinforced the understanding of wave mechanics, AC circuits, and relationships between electrical components.
By working with real and simulated equipment for Lissajous figures, students also gained insight into waveform interactions, critical for various advanced engineering applications. The ability to visualize and analyze voltage signals on an oscilloscope provides invaluable experience for future work in electrical engineering and physics.

References

1. BK Precision (2020). Model 2120B Oscilloscope. BK Precision.
2. Blanco, V., et al. (2018). Fundamentals of Electrical Engineering. New York: Wiley.
3. Dorf, R. C., & Bishop, J. (2016). Introduction to Electric Circuits. Hoboken: Wiley.
4. Donnelly, K. (2016). Oscilloscope Basics: Techniques and Applications. IEEE Educational Activities.
5. Gering, J. (2020). The Oscilloscope Experiment Guide. Florida Institute of Technology.
6. Hunt, D. (2017). Electronic Measurements and Instrumentation. New Delhi: McGraw-Hill.
7. Kahn, L. (2018). Practical Oscilloscope Techniques. Cambridge: Cambridge University Press.
8. Lee, M. (2017). AC Circuits and Devices. New York: Pearson.
9. Smith, T. J. (2019). Signals and Systems. Boston: Cengage Learning.
10. Young, H. D., & Freedman, R. A. (2014). University Physics with Modern Physics. San Francisco: Addison-Wesley.