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This method works when the hard iron field is small.
PC Demo Interface Software Method
3D Calibration—This method is recommended when the hard iron field is large. The PC demo interface will collect
magnetic vector information and analyze to find the hard iron offsets.
Launch PC Demo Interface (Ver. 2.02 or higher)
In PC Demo, go to Diagnostics menu and to Perform 3D Calibration menu
In Hard Iron page, activate Read Data
You should see the Total Valid Readings (# of data points collected) go up.
If not check the following
First quit the Cal page
Go to Diagnostics \ Options \ Calibration
Select Real Time Data from Unit by clicking that option
Slowly rotate the platform through a full circle in a gentle motion while changing roll and pitch as much as the
platform will allow. Generally this procedure will take over two minutes.
At the end of this procedure hit Stop.
Once the computation is complete hit Apply to put the Hard Iron offsets into the unit.
If sufficient tilt change were not encountered during the calibration procedure, then the calculated Zoffset value may not
be reliable. In such case the Z offset will appear in red, and the corresponding check box empty. User has the option to
accept this value by checking the box.
Z Reference Method—In applications which changing the tilt of the host is not possible, an approximate value of the
Zoffset can be found by using the Z Reference Method. This method directly compares the Z component of the earth's
magnetic field in an undisturbed location to that of the host.
This procedure involves two steps:
Step 1. Collect Z reference value near the calibration site, away from large metal objects that will distort the earth's
field by:
Activating Diagnostics \ Capture/Clear Z Reference
Hit Read Data
Hold the compass approximately level
Hit Stop after capturing 10-20 readings and hit 'Apply' to save the new Z Reference value in the EEPROM of
HMR3000.
Step 2. Install the compass on the host and follow the normal 3D Calibration described above. Mag Z offset will be computed
from the Z Reference method as well as the normal method, and the most appropriate value is indicated by a cross mark against
the value.
Goodness of Calibration—At the end of each calibration, PC Demo calculates and reports a variation number; the lower
the number the better the calibration. The compass should be relocated if the variation number is greater than 40.
3.0 OPERATION OF THE HMR3000 IN DETAIL
3.1
GENERAL
The HMR3000 consists of three magnetoresistive magnetic sensors and a liquid filled two-axis tilt sensor to produce tilt
compensated heading data. A microprocessor controls the measurement sequence of the sensors, and all the parameters
that control the operation are stored in an EEPROM. The output sentences of the HMR3000 conform to the NMEA 0813
standard for Marine communication.
900240 Rev. B
3/01
page 6
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