Introduction; Product Description; Operation; Installation - WATSON INDUSTRIES AHRS-S305 Owner's Manual

CAUTION!
Watson Sensors are rugged devices that have been used successfully in a number of harsh
environments. The components have been qualified to withstand a mechanical shock of 500g 's
or greater, and most enclosures provide an added level of protection. However, dropping a
sensor from waist height onto a hard floor can cause a shock level of 600g's. At this level,
damage is likely to occur.

Introduction

This manual is intended to help in understanding the installation and operation requirements of
the Watson Attitude and Heading Reference System.

Product Description

Attitude and heading gyros need frequent correction to compensate for the 15º per hour of earth
rotation. Watson Industries has produced a solid-state gyro system, which models these
functions for an attitude gyro and a slaved heading gyro. This system uses a microprocessor to
integrate angular rate sensor data and provides a closed loop system of error correction to adjust
biases from earth rotation and from instrument offsets. Interface to the microprocessor is done
through a 16-bit A/D and a 14-bit D/A converter. The solid state vibrating structure angular rate
gyros used in this system provide extremely high reliability, low power consumption, shock
resistance and low cost.

Operation

The angular rate sensor signals are coordinate transformed and then integrated to produce
attitude and heading outputs that reflect normal attitude coordinates. These attitude and heading
signals are compared against three accelerometers and a triaxial fluxgate magnetometer to derive
short-term absolute errors. These errors are filtered over a long time constant and are used to
adjust biases in the system so that the long-term convergence of the system is to the vertical
references and the magnetic heading. Compensations for centrifugal forces and velocity changes
on the accelerometers are used to improve overall stability and accuracy.

Installation

Orientation:

This device utilizes an earth's magnetic field orientation sensor, so orientation is important. The
base plate of the AHRS is intended to be mounted on top of a horizontal surface with the
connector toward the forward direction of the vehicle.

Mounting:

A mounting plate is provided for a flat surface mount. Use non-magnetic hardware. Ideally, the
unit should be installed at least 4 feet away from all significant magnetic materials. Some highly
magnetic materials require even greater separation from the AHRS unit. The unit may be
adhesively mounted at any of its surfaces. If high shock loads are expected (greater than 10G or
repeated shocks greater than 5G), the appropriate shock mounting should be used to prevent
damage. Vibration isolation should be used for use in 2.5G or greater vibration environments.
Symmetry is very important in such mount designs (consult Watson Industries for application
notes on this if needed).
Watson Industries, Inc AHRS-S305 Rev J 03/22/2018
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