PNI TCM 2.6 - Manual (Page 17)

PNI Sensor Corporation DOC#1009269 r11
TCM2.5 & TCM2.6 User Manual Page 17 of 49
User Calibration
All compasses can perform well in a controlled environment, where the ambient magnetic field
consists solely of the earth’s field. In most practical applications, however, an electronic compass
module will be mounted in a host system such as a vehicle that can contain large sources of local
magnetic fields: ferrous metal chassis, transformer cores, electrical currents, and permanent
magnets in electric motors.
By performing the user calibration procedure, you allow the TCM2.5/2.6 to identify the major
sources of these local magnetic anomalies and subsequently cancel out their effects when
measuring the earth’s magnetic field for computing compass headings. When you perform the user
calibration procedure, the TCM2.5/2.6 takes a series of magnetic field measurements. It analyzes
these total field measurements in orde
r to identify the components that are created by the earth’s
field, which is the desired signal, from those components that are generated by the local
environment, which we wish to subtract out.
The end goal of the procedure for the TCM2.5/2.6 is to have an accurate measurement of the static
three-dimensional magnetic field vector generated by its host system at its mounting location. This
vector is subsequently subtracted out of run-
time field measurement to yield the resultant earth’s
field vector.
On e major benefit from the TCM2.5/2.6’s triaxial magnetometer/triaxial inclinometer system
configuration is its ability to compensate for distortion effects in all orientations throughout its usable
tilt range. As we have mentioned, a compass must measure the local field vector generated by the
host system at its current position within the system in order to accurately calibrate. Because the
TCM2.5/2.6’s magnetometer is strapped-down, or fixed with respect to its host system, this local
field vector does no
t change as the host system’s attitude changes, allowing the TCM2.5/2.6 to
accurately compensate in all pitch and roll orientations. Gimbaled fluxgates, for instance, are
unable to provide accurate calibration in non-level orientations because its magnetometers, being
gimbaled, change position with respect to the host system as attitude changes. This presents a
different local distortion field than that measured during calibration.