Experimental Methods in Structural Engineering

1. University of Illinois Urbana-Champaign Experimental Methods in Structural Engineering Devices Presentation: Accelerometers Instructor Prof. Dan Kuchma Students: Yumei Wang Cristiano Bilello 1

2. University of Illinois Urbana-Champaign Summary • Application • Types of accelerometers • Technical description • Device set-up • Other information 2

3. University of Illinois Urbana-Champaign • Dynamic loads: • Resonance phenomenon • Fatigue • Instability • Discomfort for human user Application 3

4. University of Illinois Urbana-Champaign Vibration Transducers • Displacements: LVDT,laser optical range sensors. • Velocity: Laser Vibrometer. • Acceleration: Piezoeletric, Piezoresistive and Capacitive Accelerometers. Advantage of using accelerometers • Range of application • Self generating (Piezoeletric) • Relative cheap • Easy to install • Long term stability 4

5. Model: 356B11 Miniature, 10 mV/g, 4 gm University of Illinois Urbana-Champaign Voltage Sensitivity (±10%) 10 mV/g (1,02 mV/[m/s2]) Measurement Range (for ±5V output) ±500 g pk (±4 905 m/s2 pk) Frequency Range (±5%) 2 to 10 000 Hz (Z), 2 to 7 000 Hz (X, Y) Mounted Resonant Frequency ³ 35 kHz Broadband Resolution (1 Hz to 10 kHz) 0.002 g rms (0,02 m/s2 rms) Operating Temperature Range -65 to +250 °F (-54 to +121 °C) Sensing Element Ceramic Shear Size (cubic envelope) 0.4 inch (10,2 mm) Weight 0.14 oz (4 gm) Electrical Connector 4-Pin/Side 5ft. integral cable terminating to 4 pin Mounting Thread 5-40 Female Types and Characteristics • Piezoelectric (AC, high frequencies, self generating) • Piezoresistive and Capacitive (DC, low frequencies) • Force balance (aircraft inertial navigation systems) 356B11 Miniature Triaxial ICP® Accelerometer 5

6. University of Illinois Urbana-Champaign The Piezoeletric Effect Piezoelectric material Accumulation of charged particles on the crystal. The electrical output is proportional (Sensitivity) to the applied acceleration Frequency response ao = output accelerationab = mounting base or reference acceleration 6

7. University of Illinois Urbana-Champaign VOLTAGE AMPLIFIER CHARGE AMPLIFIER High Frequency (1 MHz) Low Cost Typically used with Quartz Small Size Limited Frequency (~ kHz) More Costly Typically used with Ceramic Low Noise Signal Conditioning To properly analyze the signal from charge sensors, the output must normally be converted to a low impedance voltage signal. Voltage amplifier Charge amplifier 7

8. University of Illinois Urbana-Champaign Mounting Systems Screw mounting Stud mounting Adhesive mounting Magnetic mounting Selection criteria: test structure, frequency range, vibration level Installation time: structural dimension 8

9. University of Illinois Urbana-Champaign Device set-up Devices Location • High dynamic response (low external noise) • Full characterization of dynamic motion of the system • Minimization of the induced perturbation (small or large structure) Number of devices • data acquisition channel • human resources Economic cost Time cost 9

10. University of Illinois Urbana-Champaign Miscellaneous • Cost of accelerometers: 200$ to 1200$ (not including the set-up devices) • Not operating cost (just the poor Graduate student) • The durability depends on the quality of the accelerometers and of the users!! Accelerometers producer: • PCB Piezotronics • Brüel & Kjær • Silicon Design, Inc. • Vibra Metrics 10