Table of Contents
Advertisement
HMR3000 User's Guide
Orientation—Forward direction of the compass can be oriented at any angle from that of the platform. Use Deviation
Angle parameter to convert the compasses magnetic heading to the true or magnetic heading of the vehicle/platform.
2.11 HMR3000 Hard-Iron Calibration
All magnetic compasses have to be calibrated in order to compensate for magnetic fields other than the earth's field
components to get accurate heading. These additional magnetic fields (hard-iron effects) are generated by the near
environment and therefore depend on the compass mounting location. By performing a simple procedure, the HMR3000
can compensate for these steady, static magnetic fields. Field components found after a calibration are only valid for the
particular orientation and location of the compass. A re-calibration is necessary after a relocation of the compass or if the
platform has changed its magnetic character.
Typically hard-iron calibration is performed by following a calibration procedure specified by the manufacturer. During this
procedure the compass collects data required for the compensation algorithms. The goal of the calibration procedure is to
sample the magnetic field components for many possible orientations of the host system. Rotating the host system
through 360 degrees or driving in a circle (in the case of a vehicle) will enable the compass to sample its magnetic
environment and derive the magnetic offset and scaling numbers to null out the hard-iron effects. The HMR3000 can be
calibrated by either using the built in calibration method or by using the PC Demo Interface software program. The
calibration procedure for both these methods is the same.
2.11.1 Built-in Calibration Method
This method uses an iterative procedure to calculate the hard iron offsets. In most situations 275 iterations would produce
good results. The calibration procedure has to continue until this iteration count is reached.
To put the HMR3000 into calibration mode issue the calibration command #F33.4=0*51<cr><lf>.
Slowly rotate the host system through a full circle in a gentle motion while changing roll and pitch as much as the host will
allow. Generally this procedure will take over two minutes.
You may check the iteration count periodically during the rotation by issuing #I26C?*31<cr><lf>. HMR3000 will reply with
a #nnnn*hh<cr><lf> message, where nnnn is the value of the iteration count. If this value is less than 275 continue with
the calibration procedure until that number reaches 275.
At the end of this procedure issue a command to save the results in the HMR3000's EEPROM (#F2FE.2=1*67<cr><lf>).
Put the compass back into operate mode by issuing a #F33.4=1*50<cr><lf> command.
This method works when the
hard iron field effects are small.
2.11.2 PC DEMO Calibration Method
This method is recommended when the hard iron field effects are large. The PC DEMO software interface will collect the
raw magnetic vector information and analyze the data to find the hard iron offsets.
1. In PC Demo, go to Diagnostics menu, and then to the Perform 3D Calibration selection.
2. On calibration page, activate Read Data button. You should see the Total Valid Readings number (# of data points
collected) go up with motion.
3. 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.
4. At the end of this procedure click the Stop button. The magnetic vector offsets will display as results. Click the Apply
button to put the Hard Iron offsets values into effect. In clean magnetic environments, the offsets will be only a few
hundred counts away from zero.
8
www.honeywell.com
Advertisement
Table of Contents
