Won't time come into the equation. If I throw something in the air it will have 1G accelleration beforehand, something greater than 1G while I'm throwing it, 0G until it hits the ground and possibly many 10's of G on contact. So over what period are you computing the mean? Something subject to vibration may have very different positive and negative peak G values, depending on mounting arrangements. And computation based on sum of squares will bias the results toward the higher values. RP On 16 June 2012 21:47, Brendan Gillatt wrote= : > On 16 June 2012 09:10, Electron wrote: >> >> Hi, >> >> On a 3-axial accelerator I compute the magnitude by simple Pythagorean t= heorem >> in 3D, i.e. Mag=3Dsqrt(AccX*AccX+AccY*AccY+AccZ*AccZ) >> >> It is an analogue accelerometer with significant RC filters between its = 3 analog >> outputs and the PIC ADC. >> >> Leaving the accelerometer stationary, whatever the inclination, I measur= e 1.0g >> of course. >> >> But in the presence of strong vibrations, I measure a mean magnitude of = more than >> 2.0g! >> >> Is this theoretically even possible, or should I bughunt it? If it's the= filters, >> then I thought that the vibration would cancel out thanks to them, was I= wrong? > > Are you taking the mean before or after finding the magnitude? If > after then you will always get a positive mean. Think about it: the > magnitude of a positive and a negative acceleration will both be > positive and hence will not cancel. > > If you take the mean beforehand I'm not sure what is going on to cause > such a large error. > > All the best, > Brendan > -- > Brendan Gillatt > http://www.brendangillatt.co.uk > -- > 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 .