Sensor Calibration and Time Waveform Analysis
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Questions and Answers

How does tightening a guitar string affect the note it produces?

  • The string breaks.
  • The note goes up (correct)
  • The note remains the same.
  • The note goes down.

    • What type of damping occurs when a bicycle pump is pressed down?

  • Elastic damping.
  • Viscous damping. (correct)
  • Hysteresis damping.
  • Frictional damping.

    • What happens to a spring in a mass-spring system when forced to stretch less due to increased stiffness?

  • It moves a greater distance.
  • It vibrates faster.
  • It becomes less rigid.
  • It moves less distance. (correct)

    • What characterizes critically damped motion?

    <p>It returns to rest without oscillating.</p> Signup and view all the answers

    How does damping affect the natural frequency of a spring mass system?

    <p>It has a minor effect on frequency.</p> Signup and view all the answers

    What is the relationship between damping and velocity in a system?

    <p>Damping is proportional to velocity.</p> Signup and view all the answers

    What describes an underdamped system?

    <p>Oscillates a few times before stopping.</p> Signup and view all the answers

    What occurs when a mass moves in phase with a slower hand motion near its natural frequency?

    <p>The spring becomes rigid.</p> Signup and view all the answers

    What is the primary function of the Hanning window?

    <p>To minimize signal leakage</p> Signup and view all the answers

    If the maximum frequency (Fmax) is 1000 Hz, what will the sampling rate (Fs) be?

    <p>2560 Hz</p> Signup and view all the answers

    How many impacts are observed in 0.2 seconds given approximately 5.8 impacts occur during that time?

    <p>6 impacts</p> Signup and view all the answers

    What is the time period of each impact if there are approximately 5.8 impacts in 0.2 seconds?

    <p>0.034 seconds</p> Signup and view all the answers

    What is the bandwidth (BW) if the resolution (R) is 1.25 Hz and the waveform factor (WF) is 1.5?

    <p>1.875 Hz</p> Signup and view all the answers

    If there are 800 lines of resolution (LOR) and Fmax is 1000 Hz, what is the calculated value of N?

    <p>2048</p> Signup and view all the answers

    What is the time taken for one revolution if an object rotates 20 times per second?

    <p>0.05 seconds</p> Signup and view all the answers

    What percentage overlap is commonly used with linear averaging on typical machines?

    <p>50%</p> Signup and view all the answers

    What is the approximate phase lag of the heavy spot compared to the critical speed in the given scenario?

    <p>80 degrees</p> Signup and view all the answers

    In a single degree of freedom system (SDOF), which components are included?

    <p>Mass, spring, and damper</p> Signup and view all the answers

    How is the natural frequency defined in a multi degree of freedom (MDOF) system?

    <p>As each natural frequency coincides with an SDOF</p> Signup and view all the answers

    What is the characteristic of nodes in a mode shape of a structure?

    <p>Nodes do not move</p> Signup and view all the answers

    What might you expect if a diving board is in resonance?

    <p>It would vibrate differently in vertical and horizontal directions</p> Signup and view all the answers

    What is an Operational Deflection Shape (ODS)?

    <p>An animation that shows vibration</p> Signup and view all the answers

    What forms the basis of resonance in a system like a diving board?

    <p>The natural frequency matching excitation frequency</p> Signup and view all the answers

    What is the primary factor affecting how a structure vibrates?

    <p>The mode shape being excited</p> Signup and view all the answers

    What is the heavy spot on a shaft?

    <p>The angular location of the imbalance vector at a specific lateral location.</p> Signup and view all the answers

    What does the high spot on a shaft indicate?

    <p>The point on the shaft directly under the vibration transducer.</p> Signup and view all the answers

    When balancing a rotor, where should a trial weight be placed?

    <p>Opposite the heavy spot.</p> Signup and view all the answers

    What is important to note about phase readings when balancing?

    <p>The high spot lags the heavy spot.</p> Signup and view all the answers

    What does the phase reading from a Keyphasor relate to?

    <p>The high spot.</p> Signup and view all the answers

    What is the consequence of mismatched phase readings during balancing?

    <p>Balancing efforts could be ineffective.</p> Signup and view all the answers

    Why is it important to understand the relationship between the heavy spot and the high spot?

    <p>To effectively balance the rotor by compensating for the imbalance.</p> Signup and view all the answers

    What happens to the rotor as the weight passes compared to the high spot?

    <p>The rotor moves ahead of the weight.</p> Signup and view all the answers

    What is the frequency of the wave with a period of 0.005 seconds?

    <p>200 Hz</p> Signup and view all the answers

    What frequencies are present in the given waveform modulation?

    <p>180 Hz, 200 Hz, 220 Hz</p> Signup and view all the answers

    How many impulses occur in one shaft rotation?

    <p>33</p> Signup and view all the answers

    What is likely indicated by a larger pulse among the gear teeth impulses?

    <p>A damaged tooth</p> Signup and view all the answers

    How does increasing the stiffness of a spring affect the natural frequency in a mass-spring system?

    <p>It increases the natural frequency</p> Signup and view all the answers

    What must be done to adjust the phase readings of sensors pointing in opposite directions?

    <p>Add 180 degrees</p> Signup and view all the answers

    If the mass in a mass-spring system increases, what happens to the natural frequency?

    <p>It decreases</p> Signup and view all the answers

    What is the natural frequency formula related to stiffness and mass?

    <p>fn = 2π√(k/m)</p> Signup and view all the answers

    Study Notes

    Sensor Calibration

    • Use FFT algorithm to measure the time waveform and calculate the spectrum
    • The sample rate is 2.56 times the maximum frequency (Fmax)
    • Time between samples is 1/Fs
    • Number of lines of resolution (LOR) is 2.56 times the LOR
    • Time is LOR/Fmax
    • Convert Revolution Per Minute (RPM) to Hertz (Hz) by dividing by 60
    • The period is 1/frequency
    • Hanning window is used to solve leakage
    • Typical linear averaging uses 4 or 12 averages with a 67% or 50% overlap

    Time Waveform Analysis

    • Time waveform is measured in seconds
    • Frequency is 1/period
    • Modulating frequency has a period of 0.05 seconds, making the frequency 20 Hz
    • Period is 0.005 sec, making the frequency 200 Hz

    System Dynamics

    • Natural frequency (fn) is calculated by the formula fn = 1/2 pi * sqrt(k/m)
    • Increase in spring stiffness increases natural frequency
    • Decrease in spring stiffness decreases natural frequency
    • Increase in mass decreases natural frequency
    • Decrease in mass increases natural frequency
    • Viscous damping is caused by moving a piston through a fluid
    • Hysteresis is caused by internal molecular friction
    • Damping is proportional to velocity
    • Stiffness is proportional to displacement
    • Critically damped system returns to rest slowly
    • Over damped system bounces up and down forever
    • Under damped system bounces up and down a number of times before coming to rest
    • No damping system bounces up and down forever
    • Damping has a small effect on the natural frequency
    • Spring mass system has a single frequency it vibrates at
    • As you speed up the movement of your hand, the phase of the mass begins to lag that of your hand
    • Heavy spot is the angular location of the imbalance vector at a specific lateral location on a shaft
    • High spot is the angular location on the shaft directly under the vibration transducer of closest proximity
    • When balancing a rotor, place a trial weight opposite the heavy spot
    • Phase readings are relative to the high spot
    • The high spot lags the heavy spot
    • Single Degree of Freedom (SDOF) systems have one natural frequency
    • Multi Degree of Freedom (MDOF) systems have multiple natural frequencies
    • Each natural frequency of an MDOF is defined as an SDOF

    ODS, Modal Analysis and Resonance

    • An ODS simply animates the vibration of a structure
    • Each natural frequency of a complex structure coincides with a form of movement called a mode shape
    • Nodes do not move
    • Anti-nodes move the most

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    Description

    Test your knowledge on sensor calibration and time waveform analysis techniques. This quiz covers topics such as FFT algorithms, frequency calculations, and system dynamics related to natural frequency. Perfect for students studying dynamics and signal processing.

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