Vibration
(http://www.dld-llc.com/Diffraction_Limited_Design_LLC/Vibration.html)
is a new vibration spectrum analyzer using the built-in
accelerometers inside the iPhone and iPod touch. It acquires and
displays time series data, optionally removes DC bias, applies a
Hamming window and performs an FFT on each channel to produce
frequency spectra.
The accelerometer has a sensitivity of approximately 0.02g and a
range of +-2g making the iPhone and iPod touch sensitive enough to
analyze the vibration of most moving machinery.
The software was written to simulate
the familiar oscilloscope based spectrum analyzer. Sample rate and
sample delay are easily adjustable using sliders and the user can
select the length of the data acquisition and the vertical scale used
for the display. Once the settings are configured to your preference,
press the sample button and the data is acquired.
The time series display also reports the rms amplitude of each of the
individual traces as well as the rms magnitude of all three axes
combined. To see the frequency data simply touch the frequency tab at
the bottom of the screen.
The frequency data can be viewed in linear-linear, log-linear,
linear-log and log-log format. You can turn and off the display of
each axis individually. You also have the option of applying a
Hamming window. All of these options can be modified after data
acquisition making it simple to view the data in a variety of
different ways.
All of the settings are persistent so the configuration remains
consistent between runs and when you quit and restart the program.
There are two options for documentation. If a screen capture of the
amplitude and frequency screens is sufficient just press the camera
icon and both images are saved to the iPhoto library and will be
sync’d with your computer the next time you connect. For access to
the actual time and frequency data, press the send button and
Vibration will create an email with the amplitude and frequency data
embedded in the body of the email in CSV format.