AHRS500CA Series User’s Manual
Doc# 7430-0050-03 Rev. A
Page 21
7 Appendix C. Hard and Soft Iron Calibration
7.1
Hard/Soft Iron Calibration Introduction
The AHRS500CA will need to be calibrated for hard and soft iron
compensation before use with the aircraft. The AHRS500CA series use
magnetic sensors to compute heading. Ideally, the magnetic sensors would
be measuring only earth's magnetic field to compute the heading angle. In
the real world, however, residual magnetism in the AHRS500CA itself and
in your system will add to the magnetic field measured by the
AHRS500CA.
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 AHRS500CA measures any extra constant magnetic field
that is associated with the AHRS500CA or your aircraft and corrects for it
during the calibration procedure. The AHRS500CA 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 AHRS500CA. It cannot compensate for time vary ing
fields, or fields created by parts that move with respect to the AHRS500CA.
The AHRS500CA accounts for the extra magnetic field by making a series
of measurements. The AHRS500CA uses these measurements to model the
hard iron and soft iron environment in your aircraft.
7.2
AHRS500CA 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
AHRS500CA commanding it to enter the hard iron calibration process. The
aircraft will then need to be rotated through a complete circle(s) while
monitoring the BIT status using the Gyroview software. The calibration
software will determine when an adequate set of calibration data has been
acquired and notify the user through the BIT status. The entire procedure
may take several rotations of the aircraft to collect sufficient data.
For best accuracy, you should do the calibration process with the
AHRS500CA installed in your system. If you do the calibration process
with the AHRS500CA by itself, you will only correct for the magnetism
SUNSTAR传感与控制 http://www.sensor-ic.com/ TEL:0755-83376549 FAX:0755-83376182 E-MAIL:[email protected]
SUNSTAR自动化 http://www.sensor-ic.com/ TEL: 0755-83376489 FAX:0755-83376182 E-MAIL:[email protected]
