Patent ID: 8589015

Claim:
A method of calibrating a tri-axial accelerometer that provides uncalibrated outputs for X, Y and Z Cartesian axes resident in a locator that is installed on a mobile asset, comprising the steps of: a) obtaining the uncalibrated X, V, and Z axes accelerometer output data; b) determining, via a processor, in two phases and in at least one of auto and self calibration modes a coordinate transform T that is appropriate for the tri-axial orientation of the accelerometer relative to the frame of reference of the mobile asset, wherein: the transform T is a Euler transform comprising a yaw correction angle φ, a roll correction angle θ, and a pitch correction angle ψ; the mobile asset is static on a plumbed surface in a first of said two phases, in which the roll correction angle θ and the pitch correction angle ψ are calculated; and the mobile asset is moving in a second of said two phases, in which the yaw correction angle φ is calculated; c) applying said transform T to said uncalibrated X, Y, and Z axes accelerometer output data to obtain calibrated X, Y, and Z axes accelerometer data; and d) removing from acceleration data, an offset created by gravity when the mobile asset is moving on a sloped terrain, comprising the steps of: low pass filtering the Z axis acceleration data to obtain âz; calculating the terrain pitch: p=arc cos(âz/G); determining the sign (negative or positive) of the slope; and correcting said calibrated X axis acceleration data by subtracting therefrom G·sin(ρ).