AHRS500GA Series Operator’s Manual
Doc# 7430-0060-02 Rev. A
Page 3
3 AHRS500GA Description
3.1
AHRS500GA Coordinate System
The AHRS500GA will have a label on one face illustrating the
AHRS500GA coordinate system. With the connector facing you, and the
mounting plate down, the axes are defined as:
X-axis
– from face with connector through the AHRS500GA
Y-axis
– along the face with connector from left to right
Z-axis
– along the face with the connector from top to bottom
This is the default configuration for the generic AHRS500GA model. Other
coordinate frame orientations are supported given the model type
purchased, and these will be reflected in the label as well as through the
model configuration number. The axes form an orthogonal right-handed
coordinate system. An acceleration is positive when it is oriented towards
the negative side of the coordinate axis. For exa mple, with the
AHRS500GA sitting on a level table, it will measure zero g along the x- and
y-axes and +1 g along the z-axis. Gravitational acceleration is directed
downward, and thus will be defined as positive for the AHRS500GA z-axis.
The angular rate sensors are aligned with these same axes. The rate sensors
measure angular rotation rate around a given axis. The rate measurements
are labeled by the appropriate axis. The direction of a positive rotation is
defined by the right-hand rule. With the thumb of your right hand pointing
along the axis in a positive direction, your fingers curl around in the
positive rotation direction. For example, if the AHRS500GA is sitting on a
level surface and you rotate it clockwise on that surface, this will be a
positive rotation around the z-axis. The x- and y -axis rate sensors would
measure zero angular rates, and the z-axis sensor would measure a positive
angular rate.
The magnetic sensors are aligned with the same axes definitions and sign as
the linear accelero meters.
Pitch is defined positive for a positive rotation around the y -axis (pitch up).
Roll is defined as positive for a positive rotation around the x-axis (roll
right). Yaw is defined as positive for a positive rotation around the z-axis
(turn right).
The angles are defined as standard Euler angles using a 3-2-1 system. To
rotate from the body frame to an earth-level frame, roll first, then pitch, and
then yaw.
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