Vibration Sensor

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Vibration Sensor

• Qualtech Team Members
• Ernesto Suarez
• Filmson Alexander
• Wellicor Sorsor

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Who is Qualtech?

• Founded in 1993, Qualtech Systems, Inc. (QSI) is
  a recognized leader in advanced diagnostics and
  health management software solutions
• Small company based out of Wethersfield, CT
• Found at www.teamqsi.com

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Why is Qualtech doing this?

• To understand what are vibrations and how to
  model and propose elimination solutions
• Many customers in the nearby area that would like
  to eliminate vibrations, (e.g. Pratt and Whitney,
  Sikorsky , GE)
• Vibrations can destroy engines, motors, and
  nearby components

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What Qualtech needs?

• Research project
• A model of motor vibration with respect to
  angular position
• Be able to understand vibrations and know when
  high cycle fatigue will stop a motor to fix the
  problem ahead of time

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What is high cycle fatigue?

• High Cycle Fatigue (HCF) is one of the leading
  causes of engine failure in aircraft
• HCF in turbine engines occurs when vibration
  modes of parts like fans, compressors or turbine
  rotors are excited under certain circumstances,
  sometimes leading to very sudden and catastrophic
  failure.

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What is vibration?

• Vibration is an acceleration that has simple
  harmonic motion
• A vibration could have many harmonics

Animation courtesy of Dr. Dan Russell, Kettering
University
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Project Outline

• Measure vibrations in two dimensions (x and y)
• Measure angular position on the fan (?)
• Have acquisition board to upload data from the
  boards onto a polar plot
• Analyze data and see vibrations how vibrations
  act over time
• Calibrate vibration with a known imbalance and
  balance motor

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Project Specification Requirements

• Construction Limitations
• Weight Device should have negligible weight.
• Size Device should be small enough to fit in
  the palm.
• Power Limitations
• Voltage 5V DC
• Vibration Range
• Must be able to measure 0 - 1 kHz
• Must be able to withstand 35g

• RPM Range
• Must be able to measure 1500 2000 RPM
• Operational Configuration
• Will be mounted on other machinery
• Operational Environment
• -20 to 550 C temperature
• Software Requirement
• Must be able to run under windows.
• Acquisition Hardware runs on Microsoft C

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Tasks

• Measuring vibrations
• Measuring angular position
• Acquiring Data and Analysis
• Calibrate and Balance Motor

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How do we detect Vibration?

• Since vibration is an acceleration, we measure
  vibration using accelerometers
• Accelerometers vary by number of axis,
  resolution, bandwidth, and amount of gs handled.
• Accelerometers can have either Pulse Width
  Modulation (PWM) or analog output.
• Qualtech doesnt have a feel for what the g range
  of vibrations we are gonna see.

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ADXL203 and ADXL321

• ADXL203
• Sensitivity 1000 mV/g
• Sensitivity accuracy 6
• Bandwidth 2.5 kHz
• g Range /- 1.7 g
• Cost 22.50

• ADXL321
• Sensitivity 57 mV/g
• Sensitivity accuracy 10
• Bandwidth 2.5 kHz
• g Range /- 18g
• Cost 8.33

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Circuit layout

• Capacitor decouples the accelerometer from noise
  on the power supply.
• Self test option
• Vs is 5V
• Capacitor output in series at powers of 2 to have
  a movable low pass filter at the output between
  161 Hz to 5 kHz.
• 3 pole two position switch to avoid signal
  reflection back into accelerometer not in use

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PCB of alternate design

• Corrupted PDF from www.analog.com for ADXL321

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Alternate Circuit layout

• Alternate Accelerometer Design
• If we use the ADXL32x chips they would be
  interchangeable in the circuit. We would lose
  resolution on the /- 2g chip

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Low pass filter

• The frequency of vibration we will be measuring
  is around 20- 200Hz, with harmonics.
• A safe guess of five harmonics will put our low
  pass filter at 1 kHz.
• Optimizing the low pass filter
• Having the low pass filter too high will fill our
  output with unneeded noise and lower resolution
• Having the low pass filter too low will cut out
  necessary harmonics

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PCB design

• Circuit will need to be drawn up in or PCB
  express
• Will only need a two layer PCB
• All components must be measured and laid out,
  using respective pdf files from manufacturer
• After circuit is designed it must be uploaded
  into PCB express.
• PCB can be printed at this time

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Tasks

• Measuring vibrations
• Measuring angular position
• Acquiring Data and Analysis
• Calibrate and Balance Motor

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Why do we need position?

• Since we are traveling in a circle, we have to
  measure location in a polar graph
• We need to know where along the rotation of the
  motor that the vibration has occurred
• The resolution of angular position will depend on
  the sensitivity of the output of the
  accelerometers.

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Measuring Rotation

• We will set up a magnet perpendicular to a piece
  of iron. Every time the magnet passes it will
  create an electric current. Connect this to a
  load and have a voltage drop across that load. We
  can measure the voltage spikes as a pulse.
• Since we know the time between pulses and the
  distance traveled we can find the angular
  velocity. With the angular velocity known and the
  vibration known with respect to time we can know
  where on the revolution the vibration occurs.

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Alternate Angular Design

• If they angular position is not precise enough,
  we could use two magnets and measure the time the
  fan takes to go around halfway.
• Also, this alternate design can be used if the
  fan has different speeds through one rotation.

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Tasks

• Measuring vibrations
• Measuring angular position
• Acquiring Data and Analysis
• Calibrate and Balance Motor

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Data Acquisition

• The output of the accelerometers will be voltage
  of around 2V. The output of the angular position
  hardware will be a voltage pulses. The angular
  position is the independent variable and the
  acceleration will be the dependent variable.
• This data will be read into a PXI-5122 digitizer
  card installed in a PXI chassis. The programming
  language is C.
• This data will be plotted on polar plot with
  angular position as the independent variable and
  vibration (in gs) as the dependent variable.

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Wavelets

• However, if the signals we get are discontinuous
  and if they have sharp edges, we will use a
  mathematical function called wavelets.
• Wavelets are mathematical functions that cut up
  data into different frequency components, and
  then look at each component with a resolution
  matched to its scale.
• Wavelets have advantages over traditional Fourier
  methods in analyzing physical situations where
  the signal contains discontinuities and sharp
  spikes.
• We can do this in MATLAB using the wavelet
  toolbox in MATLAB.

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Vibration output polar plot
Courtesy of http//www.spectraquest.com/
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Data analysis

• Vibrations in a fan would occur at around 20-200
  Hz, taking into consideration 5 harmonics of the
  original vibration we will set our low pass
  filter to 1 kHz.
• If 5 harmonics is an overshoot, we can adjust our
  cutoff frequency of the low pass filter here by
  moving around the jumpers on the accelerometer
  board.
• The Fourier transform or wavelets of the
  frequency measurement will also be taken to look
  at vibrations in the frequency domain. The
  harmonics will be seen here.

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Tasks

• Measuring vibrations
• Measuring angular position
• Acquiring Data and Analysis
• Calibrate and Balance Motor

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Calibrate Motor with a Known imbalance

• We need to calibrate the accelerometer by adding
  a known imbalance.
• By adding a know weight on a fan blade it will
  introduce new vibrations.
• Next, we compare the two polar plots and see what
  vibrations the imbalance has caused.

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Balance Motor

• First, we need to find a ratio between the weight
  added and the difference of vibrations caused.
• Knowing the counterweight needed for balancing we
  need to find out where to place the weight, this
  will come from the polar plot
• By placing the counterweight at the right angle
  and radius we will have a smooth running fan!

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Budget
Parts Quantity Unit Price Total Price
Accelerometers 2-4 15 60
Related Components varies 10 10
Motor/Fan 1 25 25
Angular Detection Hardware 1 25 25
Acquisition hardware 1 0 0
PCB 1 0 0
Total Estimated Cost Total Budget 200 Total Budget 200 120
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Time Line
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Limitations

• Budget
• 200
• Size of final PCB and weight
• Must be negligible to not affect natural
  vibrations
• Must have components that withstand g forces
• Limited vibrations from fan
• Can only model the vibration currently have

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Conclusions

• Be able to realize when a vibration is taking
  place and stop the motor or engine before HCF
  occurs
• Be able to derive an equation describing the
  relationship between imbalanced weight and radius
  and its vibration
• Be able to understand vibrations and its
  harmonics, and have a feel for frequencies that
  it occurs at and g forces in everyday applications

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Any Questions

• Any Questions?

Courtesy of http//www.google.com images
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