On 16 June 2012 09:10, Electron wrote: > > Hi, > > On a 3-axial accelerator I compute the magnitude by simple Pythagorean th= eorem > 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 measure= 1.0g > of course. > > But in the presence of strong vibrations, I measure a mean magnitude of m= ore 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 --=20 Brendan Gillatt http://www.brendangillatt.co.uk --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .