Lab_2

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Department Of Mechanical And Industrial Engineering Signal Conditioning By RC Filter By Kisei Mano Team 1 1. Clair Wagner 2. Courage Lahban 3. Elijah Smith Date of Experiment: 5-24-2023 & 5-25-2023 Instructor: B. S. Mani ME343-011, MECHANICAL LAB-1 Summer 2023 1
Table of Contents Cover Page………………………………………………………………………………………………………………………… Page 1 Table of Contents………………………………………………………………………………………………………………. Page 2 Grading Citaria………………………………………………………………………………………………………………….. Page 3 Table of Tables…………………………………………………………………………………………………………………… Page 5 Table of Figures…………………………………………………………………………………………………………………. Page 5 Abstract…………………………………………………………………………………………………………………………….. Page 6 Introduction………………………………………………………………………………………………………………………. Page 7 Experimental systems……………………………………………………………………………………………………….. Page 8 o Equipment……………………………………………………………………………………………………………. Page 8 o Experimental description…………………………………………………………………………………... Page 12 Data and Result………………………………………………………………………………………………………………. Page 15 Discussion……..………………………………………………………………………………………………………………… Page 23 Conclusion………………………………………………………………………………………………………………………. Page 25 Bibliography……………………………………………………………………………………………………………………. Page 26 Appendix………………………………………………………………………………………………………………………… Page 27 Bonus Points…………………………………………………………………………………………………………………… Page 35 2
SIGNAL CONDITIONING BY RC FILTER AND CHARACTERISTICS ANALYSIS Grading Criteria for Lab Report 2 (Maximum Possible 50 points + Bonus 15 points ) 1. General Format ( 20 points = 2.5+7.5+2.5+2.5+5.0 ) Cover page ( 2.5 points ) Grading Criteria Table of Contents( Include Responses for Bonus points, if any, after Conclusion Table of Figures Abstract Theoretical principles (MUST include derivation - include at appendix) (7.5 points) Fourier series representation of a general signal Filtration characteristics of R-C filters: Low-pass: Gain Vo/Vi, Gain Vo/Vi in dB, Φ in degrees, cut-off frequency High-pass: Gain Vo/Vi, Gain Vo/Vi in dB, Φ in degrees, cut-off frequency Experimental system ( 2.5 points ) Schematic diagram of experimental system Photograph of the experimental setup and label its key components Results and discussions (See details below given separately) Conclusion ( 2.5 points ) Appendices ( 5 points ) Lab manual organization Photocopy of original data Detailed sample calculation Nomenclature used in report 2. Results and Discussions ( 30 points = 10.0 + 10.0 + 10.0 ) Sample calculation ( 10 points ) 3
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Include the sample calculations in Appendix From original data obtain Vo/Vi (in dB) & Φ (high pass and low pass filter) Calculate cut-off frequency of the actual RC filter; Calculate theoretical Vo/Vi (in dB) and Φ (high pass and low pass filter) Graphically compare experimental Vo/Vi (in dB) with theory (high & low pass filter) Both High pass and Low pass filter gain characteristics should be plotted on the same graph like the poster in the lab. ( 10 points ) Graphically compare experimental Φ against theory (high and low filter) Both High pass and Low pass filter phase lag/lead characteristics should be plotted on the same graph the poster in the lab. ( 10 points ) 3. Bonus: (15 points) Based on the derivations shown for the low pass filters (which was presented in class), derive the gain and phase shift relationships for a band pass filter. Table of Figures 4
Figure # Description Page # 1 Signals and noise Combined making Distorted Results 7 2 Distorted result corrected with the use of RC Filter 8 3 General Setup of low pass filter 8 4 General Setup of high pass filter 9 5 General Setup of base pass filter 9 6 Graphical Representation of All three Types of Filters 9 7 General understanding of how RC Filters Work 10 8 General Graph of Phase Lag vs Frequency of Both low pass and High pass 10 9 Overall setup of the experiment 12 10 Schematic Diagram of experimental systems 12 11 RC Filter 12 12 Frequency Counter 12 13 Frequency Generator 13 14 Oscilloscope 13 15 Gain Characteristics of Both High and Low Filter with Theoretical Plot 18 16 Phase lag Characteristics of Both High and Low Filter with Theoretical Plot 18 17 Phase lag Characteristics Plot Logarithmic Value of Frequency Ratio 19 Table of Tables Table # Page # 1 14 2 15 3 15 4 16 5 17 6 17 Abstract The abstract of this lab was to observe several frequencies the oscillator set to 8 pre-determined frequencies, 200, 500, 1000, 2000, 4000, 8000, 20000, and 40000. With these frequencies, that 5
were passing through a Low or High filter, we were able to obtain the amplitude and N values in the provided table. In the low pass filter, the received signals have lower frequencies compared to the cutoff frequency while attenuating or blocking signals. However, a high-pass filter is an electronic circuit that allows signals with frequencies above a certain cutoff frequency to pass through while attenuating or blocking signals. The next thing we did was observe the phase shift between the two frequencies to acknowledge how the filter works in this experiment. Theoretical Principles The Fourier series representation is a mathematical tool used to express a general periodic signal as a sum of sine and cosine functions of 6
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different frequencies. This Fourier series could decompose the general signal into a series of harmonically related sinusoidal components. Fourier series Reduction of General Signals: f ( x ) = d + n = 1 ¿¿ Where the coefficients a n , b n , d shown below: a n = ( 2 L ) 0 L f ( x ) cos ( 2 πnx L ) dx b n = ( 2 L ) 0 L f ( x ) sin ( 2 πnx L ) dx d = 1 L 0 L f ( x ) dx In the figure below shows how the combinations provided signal and the noise frequency results to a distorted frequency which is useless in collecting data. Figure 1: Signals And Noise Combined Making Distorted Result To correct this disturbed frequency to a proper frequency we use an RC filtering to extract the noise from the “Distorted Result” which leads to a cleaner and better frequency. (Shown in Figure 2) 7
Figure 2: Distorted Result Corrected With The Use Of RC Filter In today's science and technology, there are three types of RC Filters: Low-pass Filter The Low Pass Filter takes in disrupting high frequency and reduces the signals at lower frequency. | V out | = | V ¿ | 1 1 + ω 2 R 2 C 2 Figure 3: General Setup Of Low Pass Filter High-pass Filter The High Pass Filter takes in disrupting low frequency and reduces the signals at higher frequency. | V out | = | V ¿ | ωRC 1 + ω 2 R 2 C 2 8
Figure 4: General Setup Of High Pass Filter Band-pass Filter The bandpass filter is the combination of the lower cutoff frequency and the upper cutoff frequency. These frequencies define the range of frequencies that the filter allows to pass through. Figure 5: General Setup Of Band Pass Filter When the three RC Filters are collecting data, the graphs looks like this: Figure 6: Graphical Representation Of All Three Types Of Filters The figure below briefly shows how the RC filter works: 9
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Figure 7: General Understanding Of How RC Filters Work In this lab we need to compare the Theoretical frequency and Experimental frequency. The easiest way to compare the frequencies is to make graphs and acquire the important data sets. With the obtained values of R and C we were able to calculate the cut-off frequency ( f c ), and the f stands for the planned frequency for theoretical calculations shown below. Theoretical Gain Low Pass: ( V 0 V i ) th dB =− 10 log [ 1 + ( f f c ) 2 ] Theoretical Gain High Pass: ( V 0 V i ) th dB = 20log ( f f c 1 + ( f f c ) 2 ) Figure 8: General Graph of Phase Lag vs Frequency Of Both Low Pass and High Pass Theoretical Phase Lag Low Pass: φ TH =− tan 1 ( f f c ) Theoretical Phase Lag High Pass: φ TH = π 2 tan 1 ( f f c ) 10
For the Experimental values we need the values of the output voltage ( V 0 ), input voltage ( V i ), Phase shift (N), and Wavelength (M). These values can be acquired from the oscilloscope measurement and the equations shown below are used at the graph for comparison. Experimental Gain Low Pass: 20log ( V 0 V i ) Experimental Gain High Pass: 20log ( V 0 V i ) Experimental Phase Lag Low Pass: φ = ( N M ) 360 Experimental Phase Lag High Pass: φ = ( N M ) 360 11
Experimental System F i g u r e 9: Overall Setup of The Experiment Figure 10: Schematic Diagram Of Experimental Systems The two figures shown above are the way this experiment is set up. First the frequency generator generates specific frequency transporting to the RC Filter. Next the RC filter sends frequency data to the oscilloscope, showing the clear graph image. With this graph we were able to measure the wavelength, amplitude and phase lag. After that the oscilloscope is connected to the frequency counter, showing how much frequency is applied. Figure 11: RC Filter Box, With R = 1000Ω C = 6.6* 10 8 F 12 Figure 12: Frequency Counter
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Figure 13: Frequency Generator Figure 14: Oscilloscope g In this experiment, we only set up to the provided frequency from the RC filter. Basically the RC filter has an Low Pass side and High Pass Side, to get frequency signal the wire management needs to be set to Low in to Low Out and High in to High Out. Next we keep changing the frequencies to see what happens, and how the input filters across to the output. 13
Results And Discussion 1. Low Pass Filter Theoretical: # Frequency (plan) Cut-off frequency X-axis y-axis ( ϕ ) f f c log ( f f c ) ( V 0 V i ) th dB =− 10 log [ 1 + ( f f c ) 2 ] φ TH =− tan 1 ( f f c ) Hz Hz 1 200 2411.4 -1.0812462 -0.029771621 -0.08275 2 500 2411.4 -0.6833062 -0.18280976 -0.20445 3 1000 2411.4 -0.3822762 -0.689157489 -0.39311 4 2000 2411.4 -0.0812462 -2.273394955 -0.6924 5 4000 2411.4 0.2197838 -5.742035377 -1.02828 6 8000 2411.4 0.52081379 -10.79396573 -1.27803 7 20000 2411.4 0.9187538 -18.43775742 -1.4508 8 40000 2411.4 1.2197838 -24.41143128 -1.51058 Table 1: Calculations of Theoretical Gain values for Low Pass Filter 14
Experimental: Table 2: Calculations of Experimental Gain values for Low Pass Filter 15 # Cut-off frequency Frequency (set) Initial voltage Twice Amplitude multiplied Factor Initial voltage Twice Amplitude multiplied Factor X-axis y-axis f c f 2*Vi* (volts/cm) 2*V o *(Volts/cm) log ( f f c ) 20log ( V 0 V i ) Hz Hz Volts cm 1 2411.4 199 22.5 22.5 -1.0812462 0 2 2411.4 500 22.5 22.5 -0.6833062 0 3 2411.4 1000 22.5 21 -0.3822762 -0.59926 4 2411.4 2000 22.5 17 -0.0812462 -2.43467 5 2411.4 3981 21.5 10.6 0.2197838 -6.14265 6 2411.4 8010 21.5 6 0.5208137 9 -11.0857 7 2411.4 20020 21.5 2.5 0.9187538 -18.69 8 2411.4 40398 22 1.22 1.2197838 -25.1213 Phase shift (lead '+', lag '-') Wav length φ Φ*( π 180 ) N M N/M seconds seconds   -0.00008 0.0049 -0.01633 -5.87755 -0.10258 -0.00008 0.00188 -0.04255 -15.3191 -0.26737 -0.00007 0.00094 -0.07447 -26.8085 -0.4679 -0.000055 0.000475 -0.11579 -41.6842 -0.72753 -0.000042 0.00024 -0.175 -63 -1.09956 -0.000026 0.000122 -0.21311 -76.7213 -1.33904 -0.000011 0.000048 -0.22917 -82.5 -1.4399 -0.0000055 0.000024 -0.22917 -82.5 -1.4399
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Table 3: Calculations of Experimental Phase Lag for Low Pass Filter 2. High Pass Filter # Frequency (plan) Cut-off frequency X-axis y-axis y-axis ( ϕ ) f f c log ( f f c ) ( V 0 V i ) th dB = 20log ( f f c 1 + ( f f c ) 2 ) φ TH = π 2 tan 1 ( f f c ) Hz Hz 1 200 2411.4 -1.0812462 -21.6547 1.488048 2 500 2411.4 -0.6833062 -13.8489 1.366348 3 1000 2411.4 -0.3822762 -8.33468 1.17769 4 2000 2411.4 -0.0812462 -3.89832 0.878395 5 4000 2411.4 0.2197838 -1.34636 0.54252 6 8000 2411.4 0.52081379 -0.37769 0.292768 7 20000 2411.4 0.9187538 -0.06268 0.119993 8 40000 2411.4 1.2197838 -0.01576 0.060213 Theoretical: Table 4: Calculations of Theoretical Gain values for High Pass Filter 16
Experimental: Table 5: Calculations of Experimental Gain values for High Pass Filter Table 6: Calculations of Experimental Phase Lag for High Pass Filter 17 # Cut-off frequency Frequency (set) Initial voltage Twice Amplitude multiplied Factor Output voltage Twice Amplitude multiplied Factor X-axis y-axis f c f 2*Vi* (volts/cm) 2*V o *(Volts/cm) log ( f f c ) 20log ( V 0 V i ) Hz Hz Volts cm 1 2411.4 199 22.5 2.5 -1.08342 -19.0849 2 2411.4 500 22.5 5 -0.68331 -13.0643 3 2411.4 1000 22.5 9.5 -0.38228 -7.48918 4 2411.4 2000 22.5 15.5 -0.08125 -3.23702 5 2411.4 3981 21.5 19.5 0.217716 -0.84808 6 2411.4 8010 21.5 21.5 0.521356 0 7 2411.4 20020 21.5 21.5 0.919188 0 8 2411.4 40398 22 22 1.224084 0 Phase shift (lead '+', lag '-') Wavelength φ Φ*( π 180 ) N M N/M (N/M)*360 seconds seconds   0.00115 0.0049 0.234694 84.4898 1.474625 0.0004 0.00188 0.212766 76.59574 1.336848 0.00016 0.00094 0.170213 61.2766 1.069478 0.00007 0.000475 0.147368 53.05263 0.925943 0.00002 0.00024 0.083333 30 0.523599 0.000003 0.000122 0.02459 8.852459 0.154505 0.000001 0.000048 0.020833 7.5 0.1309 0.0000003 0.000024 0.0125 4.5 0.07854
-1.5 -1 -0.5 0 0.5 1 1.5 -30 -25 -20 -15 -10 -5 0 f(x) = 0 R² = 0 Gain VS Frequency Low Pass Gain (Theoretical) Polynomial (Low Pass Gain (Theoretical)) Low Pass Gain (Experimental) High Pass Gain (Theoretical) Frequency: log(f/fc) Gain (V0/Vi) Figure 15: Gain Characteristics Of Both High and Low Pass Filter With Theoretical Plot 0 2 4 6 8 10 12 14 16 18 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Phase Lag vs Frequency Low Pass Phase Lag (Theoretical) High Pass Phase Lag (theoretical) High Pass Phase Lag (Experimental) Low Pass Phase Lag (Experimental) Frequency (f/fc) Phase Lag 18
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Figure 15: Phase lag Characteristics Of Both High and Low Pass Filter With Theoretical Plot -1.5 -1 -0.5 0 0.5 1 1.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Chart Title High Pass Theoretical Phase Low Pass (theoretical Phase) Series6 Low Pass (Experimental Phase) log(f/fc) φ Figure 16: Phase Lag Characteristics Plot With Logarithmic Value Of Frequency Ratio Conclusion In conclusion, we were able to see that the experimental value is very close to the theoretical value on the graphs. For example, in the Phase Lag vs Frequency (f/fc), it’s obvious that the experimental points and theoretical points don’t exactly match. The main reason the two types of values were close and not exact because the set frequency and predicted frequency were closely different. Also, there’s a possibility of a measurement error from the oscilloscope and other stuff that were used to collect data. In 19
the end we understand that frequencies change and there is a low chance of obtaining the perfect frequency. Bibliography Holman, J. Experimental Methods for Engineers 8 th edition . Mc Graw Hill. Zhu, C. (2009). Me 343 Laboratory Introduction . Wolfram Research, Inc. (2023, June). Fourier Series -- from Wolfram MathWorld . Wolfram MathWorld. Retrieved June 7, 2023, from https://mathworld.wolfram.com/FourierSeries.html . Storr, W. (2022a, August 6). Passive High Pass Filter . Basic Electronics Tutorials. Retrieved June 5, 2023, from https://electronics-tutorials.ws/filter/filter_3.html Storr, W. (2022b, August 6). Passive Low Pass Filter . Basic Electronics Tutorials. Retrieved June 5, 2023, from https://www.electronics-tutorials.ws/filter/filter_2.html 20
Appendix Original Data: R = 1000 C = 6.6* 10 8 LOW PASS FILTER # Frequency Input Voltage Twice amplitude Multiplication factor Output Voltage Twice amplitude Multiplication factor Phase shift (lead '+', lag '-') Multiplication factor Wav length Multiplication factor   plan set 2*V i   2*V o   N   M   UNIT S Hz Hz cm volts/ cm cm volts/ cm cm seconds/ div Cm seconds/ div                       1 200 199 4.5 5 4.5 5 -0.4 0.2EE-3 9.8 0.5EE-3 2 500 500 4.5 5 4.5 5 -0.8 0.1EE-3 9.4 0.2EE-3 3 1000 1000 4.5 5 4.2 5 -1.4 50EE-6 9.4 0.1EE-3 4 2000 2000 4.5 5 3.4 5 -1.1 50EE-6 9.5 50EE-6 5 4000 3981 4.3 5 5.3 2 -2.1 20EE-6 4.8 50EE-6 6 8000 8010 4.3 5 6 1 -2.6 10EE-6 6.1 20EE-6 7 2000 0 2002 0 4.3 5 5 0.5 -1.1 10EE-6 4.8 10EE-6 8 4000 0 4039 8 4.4 5 6.1 0.2 -1.1 5EE-6 4.8 5EE-6 Table 7: Original Data of Low Pass Filter part of Experiment 21
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HIGH PASS FILTER # Frequency In put Voltage Twice amplitude Multiplication factor   Output Voltage Twice amplitude Multiplication factor Phase shift (lead '+', lag '-') Multiplication factor   plan f' set 2*V i     2*V o     N   UNIT S Hz Hz cm volts/cm   cm volts/cm   Cm seconds/div                       1 200 199 4.5 5 22.5 0.5 5 2.5 2.3 0.0005 2 500 500 4.5 5 22.5 1 5 5 2 0.0002 3 1000 1000 4.5 5 22.5 1.9 5 9.5 0.8 0.0002 4 2000 2000 4.5 5 22.5 3.1 5 15.5 1.4 0.00005 5 4000 3981 4.3 5 21.5 3.9 5 19.5 2 0.00001 6 8000 8010 4.3 5 21.5 4.3 5 21.5 0.3 0.00001 7 20000 20020 4.3 5 21.5 4.3 5 21.5 0.5 0.000002 8 40000 40398 4.4 5 22 4.4 5 22 0.3 0.000001 Table 7: Original Data of High Pass Filter part of Experiment Detailed Sample Calculation : f c = 1 2 π R C = 1 2 1000 6.6 10 8 = 2411.438532 Theoretical Gain Low Pass: 22
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( V 0 V i ) th dB =− 10 log [ 1 + ( f f c ) 2 ] =− 10log [ 1 + ( 200 2411.438532 ) 2 ] =− 10log [ 1 + ( 0.082938046 ) 2 ] =− 10log [ 1.00687871 Theoretical Gain High Pass: ( V 0 V i ) th dB = 20 log ( f f c 1 + ( f f c ) 2 ) = 20 log ( 200 2411.438532 1 + ( 200 2411.438532 ) 2 ) = 20log ( 0.082938046 1 + ( 0.082938046 ) 2 ) = 20log ( 0.08293804 1.0068787 Theoretical Phase Lag Low Pass: φ TH =− tan 1 ( f f c ) =− tan 1 ( 200 2411.438532 ) = ¿ tan 1 ( ¿ 0.082938046 )=− 0.082748658 ¿¿ Theoretical Phase Lag High Pass: φ TH = π 2 tan 1 ( f f c ) = π 2 tan 1 ( 200 2411.438532 ) = π 2 tan 1 ( 0.082938046 ) = 1.488047669 Experimental Gain Low and High Pass: 20log ( V 0 V i )= 20log ( 4.5 4.5 ) = 20log ( 1 ) = 0 Experimental Phase Lag Low Pass: φ = ( N M ) 360 ( π 180 ) = ( 0.00008 0.0049 ) 2 π =− 0.102582617 Nomenclature: Symbol Description f F requency motor f c Cut-off F requency C Capacitance dB Decibels 23
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Hz Hertz M Period N Phase Shift R Resistance V i Input Volt V o Output Volt ϕ φ Phase Change π 3.141592 ME 343 Laboratory Instructions Safety Hazards Instrumentation Laboratory Room 214 HAZARD: Rotating Equipment / Machine Tools Personal Protective Equipment : Safety Goggles; 24
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Standing Shields, Sturdy Shoes. Personal Care 1. Do not wear loose clothing, Neck Ties/Scarves; Jewelry (remove). 2. Tie back long hair. HAZARD: Heating – Burns Personal Protective Equipment : High temperature gloves; High temperature apron. HAZARD: Electrical - Burns / Shock Personal Care: Take Care while doing electrical connections, particularly with grounding; do not use frayed electrical cords. HAZARD: Water / Slip Hazard Personal Care: Clean any spills immediately. HAZARD: Noise Personal Protective Equipment: Ear Plugs Rotation Speed Measurement and General Data Analysis Objectives: 1. Least square method application (Linearity) 2. Random Data Analysis (Gaussian Distribution): Rotation speed measurement by Digital Tachometer 3. Noise Filtration: Characteristics of High and Low pass RC Filter 4. Additional methods of rotational speed measurement a. Stroboscope 25
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b. Oscilloscope Direct Measurement c. Lissajou Figures Major Equipments : D.C. Generator with Magnetic Pickup Output and D.C. Motor; Electronic Frequency Counter; Digital Multimeter; Electronic Tachometer; Stroboscope; Oscilloscope; Function Generator; Hi/Lo RC Filter Procedure : A. Least Square Method Application (Linearity) a. Connect magnetic pickup to electronic frequency counter. The counter measures rotation speed in revolution per minute (rpm), as the gear on the motor shaft has 60 teeth, which produces 60 counts per revolution. b. Connect D.C. generator to digital voltmeter. Set motor speed to 1500 rpm on the electronic frequency counter with the motor speed control knob. c. Turn the D.C. amplifier knob to 15.0 Volts and lock the knob on Test Rig. d. Adjust the motor speed from 1500 to 0 rpm in interval of 300-rpm, at each point, record the electronic frequency counter reading and voltage. B. Random Data Analysis: Rotating Speed by Digital Tachometer Caution : Use minimum pressure needed to record the actual shaft speed, in order to minimize the loading error and to avoid damage to the equipment. 1. Set the motor speed to 1000 ± 10 rpm (as read on the electronic frequency counter). 2. Repeat the first step at least for 60 measurement data with each member of the team should record at least 15 readings with the digital tachometer. C. Additional Methods for Rotational Speed Measurement a. Stroboscope i. Set motor speed to 1000 rpm and record the electronic frequency counter reading. ii. Set the stroboscope frequency to approximately the electronic frequency counter reading by fine-adjust the stroboscope frequency, until the timing mark appears stationary. Record the stroboscope reading, and sketch the mark on the gear face (or take a picture for record). 26
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iii. Without changing the motor speed, increase the stroboscope frequency until it is doubled. Record the stroboscope frequency. Sketch the timing mark pattern (or take a picture for record). iv. Repeat step “c” for a stroboscope frequency of 3 and ½ times true shaft speed . b. Lissajou Figures i. Connect the output of the electronic frequency counter to the vertical amplifier of the oscilloscope. ii. Set the motor speed to 1500 rpm, adjust the vertical amplifier gain until a 4 or 5 cm peak-to-peak sine wave appears on the screen. The time sweep setting can be set at any convenient value. iii. Leave the motor speed and all the setting which you just made unchanged; but temporarily disconnect the input to the vertical amplifier of the oscilloscope. Turn your attention now to the horizontal amplifier of the oscilloscope as explained below. iv. Connect the output of the audio-oscillator to the horizontal amplifier of the oscilloscope. v. Adjust the oscillator frequency to equal approximately the frequency of the electronic frequency counter output. Turn the trigger control to the x-y position. vi. Adjust either the amplitude setting of the oscillator or the gain setting of the horizontal amplifier of the oscilloscope, or both, until the resulting display on the oscilloscope screen will be a “line” of approximately 5 cm length. vii. Re-connect the output of the electronic frequency counter to the vertical amplifier of the oscilloscope. The resulting Lissajous figure should remain essentially stationary, although it will be subject to some fluctuation. viii. Sketch the Lissajous figure (or take a picture for record) and record both oscillator frequency and motor speed from the electronic frequency counter. ix. Increase the oscillator frequency until a double loop figure appears (leaving the motor speed unchanged). Sketch the Lissajou figure (or take a picture for record) and record both oscillator frequency and motor speed from the electronic frequency counter. 27
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x. Decrease the oscillator frequency until another double loop figure appears. Sketch the Lissajou figure and record both oscillator frequency and motor speed from the electronic frequency counter. xi. Leave the oscillator frequency unchanged, and change the motor speed until a single loop appears. Sketch the figure and record oscillator frequency and the motor speed from the electronic frequency counter. D. Signal to Noise Ratio Improvement by RC Filter a. Set oscillator (frequency generator) to 1000 Hz. b. Connect the output to the electronic counter and to the input terminals A & B of the low pass RC filter and also to CH 1 of the oscilloscope. c. Adjust the vertical gain to produce a suitable (say 4.0 com peak- to-valley) display. d. Connect the output of the low-pass filter to CH 2 vertical input of the oscilloscope. Record: i. Vertical peak-to-valley CH 1 display (cm) and gain setting (volts/cm). ii. Vertical peak-to-valley CH 2 display (cm) and gain setting (volts/cm). iii. Phase lag of the filter output signal with respect to the filter input signal, i.e. record “M” and “N” (see Fig.4). Note: φ = (N)(360)/M, where φ = phase angle in degrees. (In Fig.4, there is a phase lag φ is negative) Note: Gain Controls must be in “detent position!! Repeat the above for the following oscillator frequency settings: (making sure that the input signal amplitude remains unchanged). 200; 500; 1,000; 2,000; 4,000; 8,000; 20,000; 40,000 Hz Repeat the above measurements for the high pass filter. Clearly note what lags (or leads) what. 28
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Bonus Question Based on the derivations shown for the low pass filters (which was presented in class), derive the gain and phase shift relationships for a band pass filter. Figure : Bonus question Bandpass RC Filter Schematic Diagram For Low pass: i ( t ) = v i ( t ) v 0 ( t ) R 1 = C 2 d v 0 ( t ) dt v i ( t ) v 0 ( t ) = R 1 C 2 d v 0 ( t ) dt v i ( t ) = v 0 ( t ) + R 1 C 2 d v 0 ( t ) dt ……………………………...equati on 1 For High pass: 31
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i ( t ) = v 0 ( t ) R 2 = C 1 d v i ( t ) d v 0 ( t ) dt v 0 ( t ) = R 2 C 1 d v i ( t ) d v 0 ( t ) dt R 2 C 1 ( d v i ( t ) ) dt = R 2 C 1 d v 0 ( t ) dt + v 0 ( t ) ……………………………...equa tion 2 Form equation 1 and 2 d dt ( v i ( t ) ) = d dt ( v 0 ( t ) + R 1 C 2 d v 0 ( t ) dt ) d dt ( v i ( t ) ) = d dt ( v 0 ( t ) ) + R 1 C 2 d 2 v 0 ( t ) d t 2 d dt ( v i ( t ) ) R 1 C 2 d 2 v 0 ( t ) d t 2 = d dt ( v ¿¿ 0 ( t ) ) ¿ ……………………………... equation 3 d dt ( R 2 C 1 ( d v i ( t ) ) dt )= d dt ¿¿ R 2 C 1 d 2 d t 2 ( v i ( t ) )= R 2 C 1 d 2 d t 2 ( v ¿¿ 0 ( t ))+ d dt ( v ¿¿ 0 ( t ) ) ¿¿ R 2 C 1 d 2 d t 2 ( v oL ( t ) ) R 2 C 1 d 2 d t 2 ( v ¿¿ 0 ( t ))= d dt ( v ¿¿ 0 ( t ) ) ¿¿ ……………………………...equation 4 Plugging in equation 3 and 4: R 2 C 1 ( d v i ( t ) ) dt = ( R 2 C 1 + R 1 C 2 ) d v 0 ( t ) dt + v 0 ( t ) + ( R 2 C 1 R 1 C 2 ) d 2 dt 2 ( v 0 ( t ) ) With the use of inverse Laplace, we were able to get: 32
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V 0 V i = 1 ( 1 + R 1 R 2 + C 1 C 2 ) 2 + ( 2 πf R 2 C 1 1 2 πf R 2 C 1 ) 2 33
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