At 15.58 2012.06.16, you wrote: >Quoting Electron : > > >Hi, e:- > >Are you sure that your accelerometer is not clipping in any axis >under vibration + gravity conditions? It was at first (+/- 1.5g) but then I've configured it to +/- 6.0g and clipping wasn't a problem anymore, but the imbalance persisted. Low pass filtering it (either digitally via a FIR filter or electronically via RC network) only made things worse, i.e. the imbalance remained. I even tried with my Samsung Galaxy and an accelerometer graph plot app, the problem existed also there (and I assume they took care of aliasing too). Thinking of it, I realized that there's no guarantee that vibrations will cancel out. These vibrations ultimately originate from the piston, if you imagine it as a hammer, the peak they generate may well be e.g. mostly positive, like a sinc() not like a sin() hence the contribution to magnitude will not cancel out no matter how you filter it. Even using a FIR filter didn't really help. I'm guessing it's physics, i.e. to filter those vibrations out it would be necessary some complex adaptative filter or AI algorithm. Anyone else shares my thoughts? I never imagined it could end up like this, but experimentally it really seems so now. Cheers, Mario >--sp > > >> Hi, >> >> On a 3-axial accelerator I compute the magnitude by simple =20 >> Pythagorean theorem >> in 3D, i.e. Mag=3Dsqrt(AccX*AccX+AccY*AccY+AccZ*AccZ) >> >> It is an analogue accelerometer with significant RC filters between =20 >> its 3 analog >> outputs and the PIC ADC. >> >> Leaving the accelerometer stationary, whatever the inclination, I =20 >> measure 1.0g >> of course. >> >> But in the presence of strong vibrations, I measure a mean magnitude =20 >> of more than >> 2.0g! >> >> Is this theoretically even possible, or should I bughunt it? If it's =20 >> the filters, >> then I thought that the vibration would cancel out thanks to them, =20 >> was I wrong? >> >> Cheers, >> Mario >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > > >--=20 >http://www.piclist.com PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .