ENME 351 - Assignment 6

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Johns Hopkins University *

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Mechanical Engineering

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Apr 3, 2024

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ENME 351 Assignment #6 Mitchell, Spring 2024 Page 1 of 3 ENME 351 – Electronics & Instrumentation II: Spring2024 Department of Mechanical Engineering Due Date Thursday, March 7 th , 2024 Submission Information Submit via Gradescope by 11:59 pm Include your name, UID, date, assignment number, and signature on the top of the first page. Clearly identify your final answers to each problem by drawing a box around each answer. No credit will be awarded for ambiguous answers. Question #0.1 (0 points) A general theme of my teaching philosophy is that I am here for you, the student, and continually strive to add value to your academic experience. In this spirit, please log onto ELMS and respond to the “Mid- Semester Feedback Survey” located under \Quizzes. All feedback is anonymous (I have no indication who submits what information) and is gathered with the intent of improving the quality of ENME 351 such that you get the maximum benefit out of the course. Please complete by Thursday March 7 th . Problem #0.2 (nothing to submit) Continue to give thought to what circuit you would like to explore for Lab 9. Take note of the grading rubric! The intent of Lab 9 is to showcase your comprehensive knowledge of mechatronics, in a creative and unique fashion. Looking for inspiration? There are a host of prior student Lab 9 videos available on the course YouTube channel. Reminder: no vertical videos in ENME 351! Problem #1 (5 points) A pressure sensor is used in a mechatronic circuit where the ambient pressure varies with a frequency between 1 and 3 Hz. If the sensor has a time constant of 15.4 msec, what magnitude error can be achieved? Problem #2 (6 points) Use the fft( ) function in Matlab to compute the discrete fourier transform of the wav files posted on Canvas. There are some tricks to using the fft function in Matlab outlined in the Matlab code plotFFT.m, also available on Canvas. You will need to modify it to import the wav file you are interested in using.
ENME 351 Assignment #6 Mitchell, Spring 2024 Page 2 of 3 Audio files were downloaded from http://www.vibrationdata.com/audio.htm and if required, converted using http://media.io/ . * Disclaimer * It is important that you digest and understand how plotFFT.m operates, as you may be required to modify the code (slightly) to make it work on your machine. a) What frequency is the tuning fork designed to resonate at? b) What does the amplitude spectrum plot of white noise look like? Why is it called “white” noise? (Hint: Think about white light!) c) What is the dominant frequency in a cicada chirp? Problem #3 (5 points) The relevant table from the datasheet for an MPX2010 MEMS pressure sensor is copied below for convenience. Assume you are operating at V s = 10 V, and ambient temperature = 25 o C. a) What is the range of pressures that you can measure with this sensor? b) What is the typical output voltage when the sensor measures 7.5 kPa? c) If you connected this sensor directly to the 10-bit ADC on your Arduino, operating at 5V, what pressure resolution can you achieve?
ENME 351 Assignment #6 Mitchell, Spring 2024 Page 3 of 3 Problem #4 (2 points) You have collected the following data from two different temperature measurement systems placed in boiling water. In Matlab, plot the data from both sensors together on a single figure, then compute (using calculations) and compare (using words) the accuracy and precision of each system. Include your MATLAB plot and your MATLAB code in your submitted homework. ( Reminder: all submitted work must be your own ) Sample # 1 2 3 4 5 6 7 8 Temp Sensor #1 (in o C) 100.2 98.0 97.6 98.1 98.3 99.0 99.7 101.4 Temp Sensor #2 (in o C) 98.4 98.7 98.3 99.0 98.8 98.7 98.5 98.9 Problem #5 (2 points) After viewing the following video on Fourier Transforms, fill in the blank as described in the video: https://www.youtube.com/watch?v=spUNpyF58BY “This is important…there are two different frequencies at play here. There’s the frequency of our signal, which goes up and down 3 times per second. And then, separately, there’s _______________________ _______________________________________________________________. Which at the moment is half of a rotation per second.”
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