My signal's base line is around 1. When I apply Butterworth high pass filter with cut off frequency Fc = 2Hz signal's base line drops to 0. My data are from the accelerometer. Is this behavior normal ?
Also, an accelerometer has a very flat frequency response till its (high frequent) resonance point.
But as the name gives away; the sensor provides you with acceleration data. If you want to know velocity, you need to integrate the signal once, and if you want to know displacement, you need to integrate the signal twice.
Each integration step adds a pole at zero and gives a drop-off of 6 dB per octave.