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Limitations of earthquake detection with the E-puck's accelerometer. ?. Par Rodrigo De Pablo Peña et Fabian Baerenbold. Introduction. Theoretical part Functioning Measure limitations Earthquakes Experimental part Choose a test-frequency and design a filter
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Limitations of earthquake detection with the E-puck's accelerometer ? Par Rodrigo De Pablo Peña et Fabian Baerenbold
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
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
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]
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
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
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
“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.
“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.
Relative amplitude responseMobile experiment !!! MATCH !!!
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…