29
Radian Motion Sensor
User Manual
Document Ref: UM-8041-C1
Issue: C - Rev 1
© Sonardyne International Limited 2007
Note
Note
6 Magnetic Calibration
In this section…
This section contains the following sub-sections:
6.1 “Introduction” beginning on page 29.
6.2 “Calibration” beginning on page 29.
6.3 “Troubleshooting” beginning on page 33.
6.1 Introduction
Radian uses an internal earth magnetic field sensor, called a magneto-resistive
thin film device, to detect the earth’s magnetic field so that it can deliver meas-
urements of magnetic heading.
Like any magnetic compass, Radian’s heading measurements will be affected by
the presence of any hard and soft iron on the supporting vehicle or platform on
which Radian is installed. Hard iron effects are permanent magnetisations; soft
iron effects are induced magnetic fields, induced for example by the earth’s fields.
Such effects will cause a local distortion in the earth’s magnetic field, and will de-
grade the accuracy of heading measurements if left uncorrected.
The simple self-calibration procedure described in this section of the manual al-
lows Radian to measure and compensate for ferromagnetic objects attached to Ra-
dian. The effects of any ferromagnetic objects not rigidly attached to Radian, or
any constant fields, cannot be compensated. These static effects are compensated
by the magnetic variation, which you enter through the Radian Tool
Settings
di-
alog.
The magneto-resistive devices used by Radian have a sensitivity from –100mT to
+100mT. Following a successful calibration, they will be able to respond clearly
to the earth’s magnetic field strength of 65mT without risk of saturation.
6.2 Calibration
Any calibration procedure that corrects for the effects of a local static dis-
tortion in the earth’s magnetic field must be repeated if that distortion
changes for any reason. Typically, this will be necessary if Radian is
moved, or if a large part of the vehicle moves.
Procedure
Follow the steps below to complete a magnetic calibration:
For optimum performance, perform the calibration procedure at the intend-
ed operating supply voltage.
1. Make sure Radian is connected to one of the PC’s COM ports and is working
correctly.
2. Use the Radian display program to set the baud rate to 115200 as described
on page 19, and then close the program.
3. Double-click the
MagField Mapper
icon on the desktop to start the Magfield
Mapper program.
