Physics 434 Module 3

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Physics 434 Module 3

• Acoustic excitation of a physical system

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The theme of the next three weeks
Physical system(the tube)
Input signal
Output signal

• This week operate in the frequency domain
• For a given frequency, what is the response?
  (resonances, etc.)
• Next week time domain
• Excite with a pulse, measure response
• Following week fourrier transform
• Relate to frequency domain measurement

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First, a little pre-test
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Goals for this module

• Control and monitor an applied frequency
• Detect and measure a sound wave
• Generate set of RMS values vs. frequency
• Fit resonances to determine resonant frequencies
  and Q values
• Check speed of sound from resonance difference

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Step 1 just electronics
Signalgenerator
scope
Breakout box ach0/ach8dac0
Microphone, speakerAmplifiers
microphone
tube
speaker
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Step 1, cont

• Adjust amplifier gains for given input (1 V) so
  that output does not saturate between 500 and
  2000 Hz
• Note the resonant frequencies for later check

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Step 2 test the output

• Get SoundGenerator.llb from web
• Note that it contains several VIs
• SoundGenerator(select)
• Generate a continuous signal with selectable
  frequency
• SoundGenerator(sweep)
• Generate a sequence of discrete frequencies
• acquire_test
• Monitor and measure the signal acquired by the
  DAC
• Look at the output on the scope, verify the
  frequency, feed it to your microphone, verify
  that it does not saturate.

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The AT-E board
2048
512
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Step 3 check the data acquisition

• Another self-contained VI, acquire_test.vi,
  acquires a waveform, with adjustable sampling
  rate and sample size..
• The output is graphed and analyzed by a
  simple-minded RMS vi.
• Check that the RMS of the signal generator
  output, or the output from the DAQ card is stable
  and does not vary with input frequency (500-2000
  Hz). (We do not actually measure this, but assume
  that it does not change.

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Step 4 assemble your VI and run it

• Easy to cut and paste from the two test VIs
• Must create a table of (actual) frequencies and
  RMS response from the microphone, with constant
  input to the microphone.
• Display on an XY graph
• Write to an file with the Write To Spreadsheet
  File vi from the All Functions File I/O menu.

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Step 5 Analyze the resonance peaks

• This is a new VI that you must write, capable of
  reading data from the file and fitting it see
  test_resonance_fit.vi, with sub-vi
  resonance_fitter.vi for the fitting piece that
  you may use.

Note it must select a range over which the
resonance is valid. The formula
Watch for this guy!
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Submit your vis in an llb

• Save plots with current value
• Use documentation for descriptions.
• Analysis VI should have a table of the resonance
  parameters, and your estimate of the speed of
  sound