EET-117_LAB_9__F21[1] Completed

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Centennial College *

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Electrical Engineering

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Feb 20, 2024

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Centennial College ELECTRICAL ENGINEERING TECHNICIAN & TECHNOLOGY Course: EET-117 Name Tabassum Sadia Student Number 301364890 Date November 22, 2023 Lab #9 SINE WAVE MEASUREMENT Based on Experiments in Basic Circuits by David Buchla Objectives: After performing this experiment, you will be able to: 1. Explain the four major groups of controls on the oscilloscope. 2. Use an oscilloscope to measure ac and de voltages. 3. Measure the period and frequency of a sine wave using an oscilloscope. Required Instruments and Components: Power supply DMM (Digital Multi-meter) Oscilloscope Breadboard Alligator test leads (from the EET-117 labkit) Resistors: 2.7 kΩ, 6.8 kΩ (from the EET-117 labkit)

Summary of Theory: The oscilloscope is an extremely versatile instrument that lets you see a picture of the voltage in a circuit as a function of time. Both analog and digital oscilloscopes have a basic set of four functional groups of controls that you need to be completely familiar with, even if you are using a scope with automated measurements. In this experiment, a generic analog scope is described. Figure 1 shows a basic analog oscilloscope block diagram, which illustrates these four main functional blocks. Fig. 1 Controls for each of the functional blocks are usually grouped together. Frequently, there are color clues to help you identify groups of controls. Look for the controls for each functional group on your oscilloscope. The display controls include INTENSITY, FOCUS, and BEAM FINDER. The vertical controls include input COUPLING, VOLTS/DIV, vertical POSITION, and channel selection (CHI, CH2, DUAL, ALT, CHOP). The triggering controls include MODE, SOURCE, trigger COUPLING, trigger LEVEL, and others. The horizontal controls include the SEC/DIV, MAGNIFIER, and horizontal POSITION controls. Details of these controls are explained in the referenced reading and in the operator's manual for the oscilloscope. Because the oscilloscope can show a voltage-versus-time presentation, it is easy to make AC voltage measurements with a scope. However, care must be taken to equate these measurements with meter readings. Typical digital multimeters show the RMS (root-mean-square) value of a sinusoidal waveform. This value represents the effective value of an AC waveform when compared to a DC voltage when both produce the same heat in a given load. Usually the peak-to-peak value is easiest to read on an oscilloscope. The relationship between the AC waveform as viewed on the oscilloscope and the equivalent RMS reading that a DMM will give is illustrated in Figure 2. Fig. 2

The amplitude of any periodic waveform can be expressed in one of four ways: the peak-to-peak, the peak, the RMS, or the average value. The peak-to-peak value of any waveform is the total magnitude of the change and is independent of the zero position. The peak value is the maximum excursion of the wave and is usually referenced to the de level of the wave. If you want to indicate that the reported value includes a de off-set, you need to make this clear by stating both the maximum and minimum excursions of the waveform. An important part of any oscilloscope measurement is the oscilloscope probe. The type of probe that is generally furnished with an oscilloscope by the manufacturer is called an attenuator probe because it attenuates the input by a known factor. The most common attenuator probe is the X 10 probe , because it reduces the input signal by a factor of 10. It is a good idea, before making any measurement, to check that the probe is properly compensated, meaning that the frequency response of the probe/scope system is flat. Probes have a small variable capacitor either in the probe tip or a small box that is part of the input connector. This capacitor is adjusted while observing a square wave to ensure that the displayed waveform has vertical sides and square comers. Most oscilloscopes have the square-wave generator built in for the purpose of compensating the probe. Sine waves can be generated from uniform circular motion. Imagine a circle turning at a constant rate. The projection of the endpoint of the radius vector moves with simple harmonic motion. If the endpoint is plotted along the x -axis, the resulting curve is a sine wave, as illustrated in Figure 3. Fig. 3 The control SEC / DIV should be carefully understood. Assuming you are not using automated measurements, you need to count the number of divisions for a full cycle and multiply by the SEC / DIV setting to determine the period of the wave. There are few simple online simulators you can use to practice and understand relationship between signal frequency and SEC/DIV and amplitude with V/DIV: https://academo.org/demos/virtual-oscilloscope/ https://www.oszilloskope.net/en/oscilloscope/

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Procedure 1. Review the front panel controls in each of the major groups. Then turn on the oscilloscope, select CH1, set the SEC/DIV to 0.1 ms/div, select AUTO triggering, and obtain a line across the face of the CRT. Although many of the measurements described in this experiment are automated in this oscilloscope, it is useful to learn to make these measurements manually. You will need to use Oscilloscope Manual or build-in help option to locate certain functions. 2. Turn on your DC power supply and use the DMM to set the output for 1.0 V. Now we will use the oscilloscope to measure this DC voltage from the power supply. The following steps will guide you: (a) Place the vertical COUPLING (AC-GND-DC) in the GND position. This disconnects the input to the oscilloscope. Use the vertical POSITION control to set the ground reference level on a convenient graticule line near the bottom of the screen. Fig. 4 An Oscilloscope GRATICULE. (b) Set the Channel 1 VOLTS /DIV control to 0.2 V/div. (c) Place the oscilloscope probe on the positive side of the power supply. Place the oscilloscope ground on the power supply common. Change the vertical coupling to the DC position. The line should jump up on the screen by 5 divisions. Note that 5 divisions times 0.2 V per division is equal to 1.0 V (the supply voltage). Multiplication of the number of divisions of deflection times volts per division is equal to the voltage measurement. 3. Set the power supply to each voltage listed in Table 1. Measure each voltage using the above steps as a guide. The first line of the table has been completed as an example. To obtain accurate readings with the oscilloscope, it is necessary to select the VOLTS/DIV that gives several divisions of change between the ground reference and the voltage to be measured. The readings on the oscilloscope and meter should agree with each other within approximately 3%.

Table 1. Power Supply Settings Volt/ DIV Setting Number of Divisions of Deflection Oscilloscope (measured voltage) DMM (measured voltage) Marks 1.0 V 0.5 V/div 2.0 div 1.0 V ((Volt/DIV)x(#ofDiv) 1.0 V - 2.5 V 2 V/div 1.3 div 2.6 V 2.61 V /10 4.5 V 2 V/div 2.3 div 4.6 V 4.64 V /10 Total: /20 4. Before viewing AC signals, it is a good idea to check the probe compensation for your oscilloscope. To check the probe compensation, set the VOLT/DIV control to 0.1 V/div, the AC-GND-DC coupling control to DC, and the SEC/DIV control to 2 ms/div. Touch the probe tip to the PROBE COMP connector. You should observe a square wave with a flat top and square. 5. Set the function generator for an AC waveform with a frequency of 1.0 kHz. Adjust the amplitude of the function generator for 1.0 Vrms as read on your DMM. Set the SEC / DIV control to 0.2 ms/div and the YOLTS/DIV to 0.5 V/div. Connect the scope probe and its ground to the function generator. Adjust the vertical POSITION control and the trigger LEVEL control for a stable display near the center of the screen. You should observe approximately two cycles of an AC waveform with a peak-to-peak amplitude of 2.8 V. This represents 1.0 Vrms- as shown in Figure 2. 6. Use the DMM to set the function generator amplitude to each value listed in Table 2. Repeat the AC voltage measurement as outlined in step 4. The first line of the table has been completed as an example. Remember, to obtain accurate readings with the oscilloscope, you should select a VOLTS /DIV setting that gives several divisions of deflection on the screen. Table 2. Function Generato r Settings Volts/DIV Setting Number of Divisions (peak-to-peak) Oscilloscope measured (peak-to-peak) Oscilloscope measured (rms) Marks 1.0 V RMS 0.5 V/div 5.6 div 2.8 V pp 1.0 V RMS - 2.2 V RMS 1 V/div 6 div 6.28 V pp 2.22 V RMS /10 3.7 V RMS 2 V/div 6 div 10.6 V pp 3.74 V RMS /10 Total: /20 7. Set the function generator for a 1.0 V PP sine wave at a frequency of 1.25 kHz. Then set the oscilloscope SEC / DIV control to 0.1 ms / div in order to show one complete cycle on the screen. The expected time for one cycle (the period) is the reciprocal of 1.25 kHz, which is 0.8 ms. With the SEC / DIV control at 0.1 ms/div, one cycle requires 8.0 divisions across the screen. This information is presented as an example on line 1 of Table 3.

Table 3. Function Generator Dial Frequency Computed Period Oscilloscope SEC/DIV Number of Divisions Measured Period Marks 1.25 kHz 0.8 ms 0.1 ms/div 8 div 0.8 mS - 83.0 kHz 0.012 ms 0.5ms/div 2 div 1 mS /10 600.0 kHz 0.0017 ms 1ms/div 1.6 div 16 mS /10 Total: /20 8. Change the function generator to each frequency listed in Table 3. Complete the table by computing the expected period and then measuring the period on the oscilloscope.

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REVIEW QUESTIONS 1. AC waveform has 2.4 divisions from peak-to-peak and the VOLTS/DIV control is set to 5.0 V/DI (a) Find V PP 10.4V Marks: / 2 (b) Find RMS voltage Marks: / 2 2. If you want to view the amplitude of an AC waveform that is 20.0 Vrms, what setting of the VOLTS /DIV control is best? Explain. The VOLTS/DIV control on an oscilloscope is used to adjust the vertical scale of the waveform displayed on the screen. It determines how many volts are represented by each vertical division on the screen. To view the amplitude of an AC waveform that is 20.0 Vrms (root mean square), you want to choose a VOLTS/DIV setting that allows you to accurately visualize the waveform without it extending beyond the screen or being too small to observe clearly. Since the waveform's RMS value is 20.0 volts, and the RMS value represents the effective value of an AC signal, it's typically used as a measure of its amplitude. Marks: / 4 3. The most accurate way to measure a waveform on an oscilloscope is to use a large portion of the display area. Why? Using a large portion of the display area on an oscilloscope to measure a waveform allows for increased accuracy due to several reasons Marks: / 4 4. An oscilloscope display shows one complete cycle of a sine wave in 4.3 divisions. The SEC/DIV control is set to 20 ms/DIV. (a) Find Period (T) 4.3 divisions * 20 ms/DIV Total time = 86 ms Marks: / 2

(b) Find the frequency 1/86hz Marks: / 2 5. You wish to display a 10 kHz sine wave on the oscilloscope. What setting of the SEC/DIV control will show one complete cycle in 10 divisions? Given that the frequency is 10 kHz (10,000 Hz) and you want to display one cycle in 10 divisions: Time per division=1/10,000 Hz×10 divisions Time per division=Time per division=1 μ s×10=10 μ s Therefore, you'd need to set the SEC/DIV control of the oscilloscope to 10 μ s per division to display one complete cycle of a 10 kHz sine wave in 10 divisions. Marks: / 4 Conclusions. The conclusion summarizes the important points of the laboratory work. You must analyze the examples to add emphasis to significant points. You must also include features and/or things you have done /benefits of a particular procedure, instrument, component, or circuit directly related to the experiment .

Marks: / 20 Rubric-Grading Criteria Max. Marks Punctuality 10 Lab Safety 20 Procedure 60 Review Questions 20 Conclusion 20 Neatness, Spelling, Grammar, and Sentence Structure 10 Total: /140

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