G900X/G950 Installation and Maintenance Manual – GRS 77 and GMU 44
Page 7-7
190-00719-00
Revision D
7.7.2 GMU 44 Magnetometer Mounting Guidelines
The GMU 44 is an extremely sensitive three-axis magnetic sensor. It is more sensitive to nearby
magnetic disturbances than a flux gate magnetometer. For this reason, observe the following distances
from objects or devices that can disturb the magnetic field. Table 7-7 specifies required distances from
magnetic disturbances for GMU 44 location.
Table 7-7. Required Distance from Magnetic Disturbances
Disturbance Source
Minimum Distance from GMU 44
Electric motors and relays, including servo motors
10 feet (3.0 meters)
Ferromagnetic structure greater than 1 kg total
(iron, steel, or cobalt materials, especially landing
gear structure)
8.2 feet (2.5 meters)
Ferromagnetic materials less than 1 kg total, such
as control cables
3 feet (1.0 meter)
Any electrical device drawing more than 100 mA
current
3 feet (1.0 meter)
Electrical conductors passing more than 100 mA
current [(must be twisted shielded pair if within 10
feet (3.0 meters)]
3 feet (1.0 meter)
Electrical devices drawing less than 100 mA current
2 feet (0.6 meter)
Magnetic measuring device (e.g. installed flux
gates, even if unpowered)
2 feet (0.6 meter)
Electrical conductors passing less than 100 mA
current [(must be twisted shielded pair if within 10
feet (3.0 meters)]
1.3 feet (0.4 meter)
Ensure that any electrical conductor that comes within 10 feet (3.0 meters) of the GMU 44 is installed as a
twisted shielded pair, not a single-wire conductor. (If possible, the shield should be grounded at both
ends.)
Use nonmagnetic materials to mount the GMU 44, and replace any magnetic fasteners within 0.5 meter
with nonmagnetic equivalents (e.g. replace zinc-plated steel screws used to mount wing covers or
wingtips with nonmagnetic stainless steel screws.)
Mechanical mounting fixtures for the GMU 44 must be rigidly connected to the aircraft structure. Use of
typical aircraft-grade materials and methods for rigid mounting of components is acceptable, so long as
adequate measures are taken to ensure a stiffened mounting structure.
Align the GMU 44 mounting rack to within 3.0° of the aircraft level reference in pitch and roll.