Vibration Experiments

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ME 3901 Engineering Experimentation

General information

Laboratory 5: Vibrational Measurements

Cell Phone Vibrations

via Analog Devices: Single and Dual Axis Automotive iMEMS

Note: These accelerometers were donated by Analog Devices

through the efforts of Professor Furlong.

he beam is deflected and then released, it will oscillate or vibrate, that is the deflection varies with time

a second-order system and can be described as periodic.

strain gage or accelerometer were attached to the beam it would generate a sinusoidal voltage output.

put amplitude would be proportional to the strain or acceleration and a period inversely proportional to

quency of vibration. Left to vibrate freely, without applied external forces, the beam will vibrate at its

ural frequency, , and its amplitude of the response will decrease with time, as energy in the system

t.


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e natural frequency can be quantified as:

ere ( ) is the mass per unit length of the beam and Cnis a constant.

Objective

e objective of this laboratory is to use a motion transducer (an accelerometer) to measure the frequency

des of your cell phone. Remember for this test, it is a forced vibration as opposed to a free vibration.

erefore, one should not see the exponential decay of the signal.

r each accelerometer test, vibration data will be analyzed to:

Determine the vibration amplitude, velocity, and acceleration in various units of measure

Determine the cell phone frequency harmonics

Compare measurement results as a function of transducer orientation (x vrs y frequency and magnitude

MEMS accelerometers

his laboratory, the state-of-the-art Analog Devices ADXL276dual-axes accelerometers will be utilize

e ADXL276 MEMS accelerometer is currently being used in a wide range of consumer, industrial, mil

d automotive applications.

e ADXL276 accelerometer has a measuring range of 35 g (g = 9.81 m/s2) and it provides analog outp

nals with sensitivity on the order of 55 mV/g (for full source voltages).
https://users.wpi.edu/~sullivan/ME3901/Laboratories/05-Vibrations/ADXL276.pdf


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e source voltage can range from 3 V to 5.25 V for operation and is capable of operating in a wide range

mperatures.

Tasks: MEMS accelerometers

ach a small strip of mounting tape onto your phone.

re (solder with safety glasses) the accelerometer tabs. (The prongs are facing INTO the paper on the

ematic below.)

ach the flat surface of the accelerometer to the mounting tape with the Y direction (Pins on right side to

left side) aligned (parallel) with the short axis of the phone.

nnect the 5 V DC source to an analog ouput channel on the USB6229BNC unit.

nnect Pin 10 and Pin 7 (X voltage output + and -) to an analog input channel.

nnect Pin 3 and Pin 7 (Y voltage output + and -) to an analog input channel.

eate a LabView VI schematic to record time-frequency data.

y several sampling rates (128, 256, 512, 1024 samples per second)

ep the number of samples the same as the sampling rate. In this mode there should be approximately th

ws of data written to file per second (A time row, another row for the x-axis information, the third row f

y-axis).


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A cantilever beam result (similar to a cell phone, but freely vibrating) is displayed below.


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ing the recorded data (and your VI), determine frequency modes of your phone.

hat are the acceleration peaks of your phone?

here a difference in frequency, amplitude, etc. between to two measured axes?

r future reference, recall our formulations:

Vibration Experiments

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