CEE511 Structural Dynamics
University of Michigan October 5, 2007
Prof. J. P. Lynch
Accelerometers
CEE511 Structural Dynamics:
October 6, 2008
Prof. Jerry Lynch
University of Michigan
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Accelerometer - Structural Dynamics - Lecture Slides | CEE 511, Study notes of Dynamics
Material Type: Notes; Professor: Lynch; Class: Structural Dynamics; Subject: Civil And Environmental Engineering; University: University of Michigan - Ann Arbor; Term: Fall 2008;
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CEE511 Structural DynamicsUniversity of Michigan
October 5, 2007^ Prof. J. P. Lynch
Accelerometers
CEE511 Structural Dynamics:
October 6, 2008
Prof. Jerry Lynch
University of Michigan
CEE511 Structural DynamicsUniversity of Michigan
Accelerometers
•^
3 accelerometer types used in civil structures:^9
Force balance accelerometers (FBA)
-^
Greatest market share
-^
Expensive at approximately $1000 per FBA
9
Piezoelectric accelerometers
-^
Popular in dynamic settings
-^
Moderate pricing at approximately $400 per accelerometer
9
Microelectromechanical system (MEMS)
-^
Represents the future
-^
Demand driven by car manufacturer
-^
Small and accurate
-^
Inexpensive $5-50 per accelerometer
CEE511 Structural DynamicsUniversity of Michigan
Piezoelectric Accelerometer
•^
Piezoelectrics are a crystalline material that:^9
Generate current when strained 9
Strain when voltage is applied
-^
Can be used with a proof mass to generate an electrical currentproportional to acceleration^9
Can not sense static (DC) acceleration fields (gravity)
2.5cm
CEE511 Structural DynamicsUniversity of Michigan
MEMS-Based Accelerometers
•^
M
icro
e lectro
m
echanical
s
ystem (MEMS) accelerometers
•^
Creation of mechanical structures only micrometers in size on siliconwafers (same process as CMOS integrated circuits)
-^
Cost advantage derived from using well developed CMOS fabricationprocess
-^
MEMS - more accurate and sensitive sensors in form factors andunit costs not previously possible
-^
Cost advantage of MEMS - integration of sensors and digitalcircuitry (like A/D conversion) all on one die
-^
Car industry (accelerometers for air bag deployment) has drivenmarket demand^9
GM will only buy sensor when they are less than $5!
CEE511 Structural DynamicsUniversity of Michigan
Analog Devices ADXL
•^
Low cost, low power 2-axis accelerometer – 10 g
•^
Balanced differential capacitors measure acceleration ofsilicon proof mass
•^
Variable bandwidth and resolution^9
Frequency range 0 - 50 Hz (Bandwidth)
Noise floor 4 mg (Resolution)
Range of linearity (+/- 10g)
Dynamic Range (in dB):
- DR(dB) = 20log(Max/Min) = 20log(10/4E-3) = 68 dB