Honeywell hmr3000 TruePoint User Manual page 22

HMR3500 User's Guide
CompassHost's rate to match.
This does not command the compass to change its baud rate. It only changes the rate used by CompassHost itself.
Although the compass can be commanded to change its baud rate, CompassHost will not issue this command.
4.14 COMPASS COMPENSATION
This menu performs and controls the compass magnetic compensation process, using the MCAL/DMCAL messages.
(See page 15.)
Status
An MCAL message with no action request is sent. The status returned is shown only in the main scrolling display.
Start
This choice sends an MCAL command to initiate the compass compensation process and also brings up the
display of Figure 9, which shows the progress of the procedure. The purpose of the compass magnetic
compensation is to determine the magnetic properties of the environment and derive factors which can be used to
compensate the compass. Without this kind of correction, a magnetic compass mounted on a vehicle, for
example, may produce substantial azimuth errors.
When the compass is performing the magnetic compensation process, it sends regular DMCAL messages reporting on its
progress. These are shown graphically in the display. During the first part of the procedure, the compass collects 16 data
points from its sensors in each of eight azimuth sectors, and it is necessary to move it slowly in a horizontal circle while
this is done. If the compass is mounted on a vehicle, it is done by driving the vehicle slowly in a small uniform circle on a
level ground. The progress bars in the upper half of the display show the status of this operation. When all points have
been collected in each sector, the module moves into the computation phase.
The computation may take a few minutes, during which the computation progress bar shows its status. When finished, the
compass module returns a figure of merit indication which is shown below the computation progress bar in the box labeled
22
Figure 9: Compass Magnetic Compensation Process
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