AHRS500GA Series Operator’s Manual
Doc# 7430-0060-02 Rev. A
Page 19
9 Appendix C. Hard and Soft Iron Calibration
9.1
Hard/Soft Iron Calibration Requirements
The AHRS500GA will need to be calibrated for hard and soft iron
compensation before use with the aircraft. Refer to the AHRS500GA
installation manual for installation calibration.
The AHRS500GA will need recalibration whenever ferrous metal
components have been replaced or moved relative to the AHRS500GA
within a 24 inch radius of the unit.
9.2
Hard/Soft Iron Calibration Introduction
The AHRS500GA series use magnetic sensors to compute heading.
Ideally, the magnetic sensors would be measuring only earth's magnetic
field to comp ute the heading angle. In the real world, however, residual
magnetism in the AHRS500GA itself and in your system will add to the
magnetic field measured by the AHRS500GA.
The extra magnetic field can create errors in the heading measurement if
they are not compensated. These extra magnetic fields are called hard iron
magnetic fields. In addition, magnetic material can change the direction of
the magnetic field as a function of the input magnetic field. This
dependence of the local magnetic field on input direction is called the soft
iron effect. The AHRS500GA measures any extra constant magnetic field
that is associated with the AHRS500GA or your aircraft and corrects for it
during the calibration procedure. The AHRS500GA can also make a
correction for some soft iron effects. The process of measuring these non-
ideal effects and correcting for them is called hard iron and soft iron
calibration. Calibration will help correct for magnetic fields that are fixed
with respect to the AHRS500GA. It cannot compensate for time varying
fields, or fields created by parts that move with respect to the AHRS500GA.
The AHRS500GA accounts for the extra magnetic field by making a series
of measurements. The AHRS500GA uses these measurements to model the
hard iron and soft iron environment in your aircraft.
9.3
AHRS500GA Hard and Soft Iron Calibration Procedure
The hard and soft iron calibration procedure is performed in place on the
aircraft using the calibration/maintenance cable provided, a portable PC
running Windows, and Gyroview software provided by Crossbow
Technology, Inc. A switch on the cable provides a signal input to the
AHRS500GA commanding it to enter the hard iron calibration process.
The aircraft will then need to be rotated through a complete circle(s) while
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