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ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Differential-Capacitance Acceler

ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Differential-Capacitance Accelerometer. Prepared by: Vikranth Ceakala Dept. of Electrical and Computer Engineering Utah State University. 3/9/2007. Outline . Reference list To probe further

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ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Differential-Capacitance Acceler

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  1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Differential-Capacitance Accelerometer Prepared by: Vikranth Ceakala Dept. of Electrical and Computer Engineering Utah State University 3/9/2007

  2. Outline • Reference list • To probe further • Sensor – Differential-Capacitance Accelerometer • Major applications • Basic working principle illustrated • A sample configuration of an accelerometer • A typical application • Major specifications • Limitations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  3. Reference list • Bishop, Robert H; The Mechatronics Handbook, CRC Press 2002 • Senturia, Stephen D; Microsystem Design • http://www.ee.ucla.edu/~wu/ee250b/ • http://www.analog.com/ ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  4. To explore further (survival pointers of web references etc) • http://www.sensorland.com/ • http://www.howstuffworks.com/ ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  5. Major Applications • Measurement of Acceleration, Velocity and Position • Monitor the health of machinery by keeping track of the vibrations. • Measure the position of an object in space. - by making use of 3 accelerometers, to measure each of the x, y and z axes. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  6. Major Applications(continued.) • Computer input devices - Mouse. - Joysticks. • Crash detection devices in automobiles. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  7. Basic working principle • Change of Capacitance due to acceleration of an object. • Acceleration changes the width of dielectric material between capacitor plates. • The change in width causes the change in capacitance. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  8. Basic working principle Diagram showing the principle of a differential capacitance system ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  9. Basic working principle A differential capacitance accelerometer in steady state. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  10. Basic working principle A differential capacitance accelerometer in action. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  11. Basic working principle • Change in Capacitance due to motion. • C1 and C2 are equal when the accelerometer is steady. • C1 and C2 change when the object moves, thus changing V0 as a function of displacement. The relation between output Voltage V0 and the displacement dx is given as. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  12. Basic working principle • Change in output frequency due to motion. Capacitance can be expressed as k is the dielectric constant, ε is the permittivity of free space, S is the area of the electrode, and h is the variable gap. • The variable gap h is a function of acceleration “a”, mass “m” and spring constant “k”. Hence we have a variable capacitance. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  13. Basic working principle • Since Capacitance C is inversely proportional to the acceleration and Frequency is inversely proportional to capacitance. • The output frequency is directly proportional to the acceleration. which is given by Where f0 is the frequency at zero acceleration, and fa is the frequency due to the change in acceleration. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  14. A Sample configuration of accelerometer ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  15. A Typical Application • Sensing change in inertia in airbag crash detection systems in automobiles. • By the analysis of acceleration, velocity and position one can detect a crash. In the above figure the irregular spikes represent a crash. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  16. Major Specifications • Two basic design configurations • Compression type • Crystal is held in by compression • Vibration varies the stress • Shear-stress type • Vibration deforms the crystal • Transducer • Outside power source is not needed, provides all the power it needs ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  17. Major Specifications • Proof mass of 0.1ugrams. • Minimum detectable beam length 0.2 angstrom. • Resonant frequency of the beam 10 to 22 kHz. • Smallest detectable change in capacitance 20 amtoF. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  18. Limitations • External power supply needed. • Additional circuitry needed for signal conditioning of the sensor output. - amplifier, ocillator and low pass filter ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  19. Thank You Vikranth Ceakala ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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