Limitations of earthquake detection with the E-puck's accelerometer

# Limitations of earthquake detection with the E-puck's accelerometer

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## Limitations of earthquake detection with the E-puck's accelerometer

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1. Limitations of earthquake detection with the E-puck's accelerometer ? Par Rodrigo De Pablo Peña et Fabian Baerenbold

2. Introduction • Theoretical part • Functioning • Measure limitations • Earthquakes • Experimental part • Choose a test-frequency and design a filter • Try to make the E-puck find a source of vibrations

3. Accelerometer – How it works • Accelerometer consists of 3 beams in series where the middle one is attached to a movable mass. The 3 beams form 2 capacitors in series. • An applied force changes position of the mass and therefore the value of the capacitors. • The capacitors values are linked to an output voltage between 0 and 3300[mV], which on the E-puck is a binary code between 0 and 4096 • The range of the E-puck's accelerometer is set to +/- 2[g], g=gravity

4. Measure limitations and noise • Resolution: • Noise RMS in data sheet : 4.7 [mV] • Noise RMS calculated : • Minimum detectable amplitude: • Maximum detectable amplitude : 2[g], (up to 2.75[g], but lessaccurateabove 2[g]) • Samplingfrequency: Up to 11[kHz]

5. Earthquakes • E-puck can recognize frequencies up to 11/2[kHz] • Frequencies of an earthquake between 0.1 and 20[Hz] => E-puck is able to measure this • E-puck detects earthquakes having amplitudes bigger than 0.02[g] (=0.2[m2/s]) if it is right by the epicenter • 0.2[m2/s] corresponds to an earthquake where “dishes in a cupboard rattle”! => E-puck is not very useful in this case

6. Experimental part

7. Signal of the razor

8. Frequency Detection - FIR Filter • Razor frequencies: 12-14[Hz] • FIR equiripple bandpass filter • Sampling frequency : 200[Hz] (to minimize the filter order) Band: 10 -16 [Hz], Filter order: 143

9. Unfiltred vs. Filtred Signal Shaking by hand (2-3[Hz]) --- Razor (13[Hz]) --- Cell phone (25[Hz]) Filter with attenuation of low frequencies of 40dB Filter with attenuation of low frequencies of 20dB

10. Unfiltred vs. Filtred Signal

11. “Bacteria” AlgorithmMobile experiment I • Goal: E-puck finds the source of vibrations • Assumption: There is a continuous drop of amplitude with distance to the source. • How: E-puck moves with constant speed. As long as the amplitude measured by the E-puck increases, it continues to move forward. If not, it changes direction. • Amplitude computation: Take the sum of the filtered signal elements squared and divide by an appropriate constant to avoid overflow. • Random term: A random term is added to the constant speed to make the E-puck able to move randomly in any direction.

12. “Bacteria” AlgorithmMobile experiment I But: Although the E-puck sometimes finds the source, it often gets stuck far away from it…. Why ? =>>> Idea: Scan the whole surface with the E-puck to have an idea of the vibration pattern of it. Then repeat the experiment.

13. Material for experiments

14. Relative amplitude responseStatic experiment

15. Relative amplitude responseMobile experiment II

16. Relative amplitude responseMobile experiment !!! MATCH !!!

17. References • http://www.naun.org/journals/geology/20-052.pdf • http://en.wikipedia.org/wiki/Japan_Meteorological_Agency_seismic_intensity_scale • http://pdf1.alldatasheet.com/datasheet-pdf/view/103487/MOTOROLA/MMA7260Q.html The end…