Help Required Regarding Velocity Estimation

Hi every one,

I m using VG440 series Inertial Measurement Unit(IMU). This IMU is 6DOF ,3-axis Accelerometer, 3-axis Gyroscopes and no magnatometer. iI have logged a file by placing it in CG(Central Gravity) point of land vehicle. It gives measurements of accelerometer in "g" ,gyroscope in "radians/sec" and angles in degrees.

I want to estimate velocity from this data. I have taken gravity vector as [0 0 -1]. I calculated rotation matrix from "angle2dcm" function in Matlab and multiplied it with gravity vector. I have named this product as "Gravity_component". Then i have found the true vehicle acceleration by subtracting the "Gravity_comp" from measured accelerometer data. Then I multiplied the result with 9.8 to convert it into m/sec2. Next I have integrated this true acceleration like this:
vel_x(i) = vel_x(i-1) + dt * a_true(i);

Is any step missing in finding velocity? My results are not upto expectation. Velocity amplitude rise to 200 in amplitude that is not true if I consider it m/sec2.

Very Urgent help is required and thanks in anticipation.

Can you post your script?

Also have you examined the raw data, do the values look realistic? I've done this kind of measurement with inexpensive accelerometer and gyro and without filtering of the raw data I could never get any sensible results (ie. speed, distance and direction).

I couldn't post my script because it is on different computer that is not attached with internet.

My values are quite in range for accelerometer. In down direction these are around -1 g and in other two directions these are between +-0.2 g.

You suggested that i should filter my raw accelerometer data to get corrected value for velocity.

If you have any idea please share it.
Regards