Accelerometer sensor

Accelerometer introduction, working, types, advantages and diadvantages are well explained for all the types of accelerometer focusing on automobile applications

1. Accelerometer sensor By Intakhab Khan (VTP2984) Under the guidance of Prof. A . Muthrasan

2. Table of contents Introduction Types Working Applications Advantages and disadvantages Manufacturers 18/05/2021 2

3. Accelerometer sensor Accelerometers are electronic sensor which are used to measure the acceleration of the vehicle in all the three axis. It converts acceleration into electrical signals and sends it to electronic control unit after amplification by which the acceleration value is interpreted. In vehicle these accelerometers helps in finding acceleration in all thee axis for vehicle control, measurement of vibration and shocks for engine control or suspension control and also used to deploy air bag during accidents. 18/05/2021 3

4. Types of Accelerometers 18/05/2021 4

5. Working A. Capacitive Accelerometer It consists of mass attached with the springs, when the vehicle accelerates the mass moves the opposite direction due to pseudo force which changes the distance of separation between plates and as we know capacitance of the capacitor is inversely proportional to the distance of separation the capacitance changes with the acceleration. This leads to change in voltage and this signal is sent to ECU which is manipulated and converted into acceleration value.   18/05/2021 5

6. 18/05/2021 6

7. 3 axis accelerometer 18/05/2021 7

8. Working B . Piezo resistive Accelerometer A piezo-resistive accelerometer has a stable structure composed on a silicon chip created by the micromachining and semiconductor production technology. A mass and a beam on which a set of the piezo-resisters are created on a silicon chip. A set of electrical bridged is formed by such piezo-resistive resisters to generate signals proportional to the applied acceleration A piezoresistive accelerometer is based on changes in electrical resistance in a strain gauge. sensors with conventional glued-on strain gauges or opt for microelectromechanical systems (MEMS) technology instead. 18/05/2021 8

9. 18/05/2021 9

10. Working C . Piezoelectric Accelerometer It works under the principle of piezoelectric effect which is piezoelectric materials produce electricity when put under physical stress. When the vehicle accelerates the force acts on the mass (Pseudo force) which leads to deformation of piezoelectric crystal structure creating the voltage across the material as per the given equation. 18/05/2021 10 g = voltage sensitivity a = acceleration A and t is area and thickness of crystal m is seismic mass  

11. 18/05/2021 11

12. Application   Automobile collision safety systems uses accelerometer. When a car is acted on by a powerful dynamic force, the accelerometer (sensing a rapid deceleration) sends an electronic signal to an  ECU, which in turn deploys the airbags.   Electronic stability control in vehicles uses Accelerometer along with gyroscope to measure the vehicle orientation and dynamic condition Vibration and shock measurement (piezoelectric) 18/05/2021 12

13. Advantages Disadvantages ➨It is simple to interface. ➨It has high impedance. ➨It offers higher sensitivity. ➨It has high frequency response. ➨It is available at lower cost due to advancement in MEMS technology ➨It uses built-in signal conditioning circuit to measure capacitance. ➨An Accelerometer measures change in velocity only. It does not measure a constant velocity. ➨An Accelerometer can not measure rotation around its own axis of movement. Due to this, it is used in conjunction with gyroscope to measure angular velocity. ➨It is sensitive to temperature and operates over limited temperature range. ➨Its efficiency degrades over time. ➨It requires external power for its operation. ➨The other disadvantages are less longevity and hysteresis error. 18/05/2021 13

14. Manufacturers BOSCH NXP MEMSIC Kionix STMicrocontrollers 18/05/2021 14

15. Thank You 18/05/2021 15