190-01115-01
G3X/G3X Touch Installation Manual - GMU 22 Installation
Rev. AC
Page 15-3
Ensure that any electrical conductor that comes within 10 feet (3.0 meters) of the GMU 22 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 22, 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 wing tips
with nonmagnetic stainless steel screws).
In general, wing mounting of the GMU 22 magnetometer is preferred (unless as noted in
Fuselage mounting is less desirable because of numerous potential disturbances that interfere with accurate
operation. For installations with dual GMU 22 magnetometers, co-locating the two magnetometers close
to each other in the tail or in one wing is recommended as this reduces the likelihood of heading splits or
miscompares when operating on the ground in the vicinity of local magnetic anomalies.
Mechanical mounting fixtures for the GMU 22 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.
Level the GMU 22 mounting rack to within 3.0° of the in-flight level cruise attitude.
Align the GMU 22 mounting rack’s forward direction to within 0.5° of the longitudinal axis of the aircraft.
In a system with more than one ADAHRS (GSU 25/73), ADAHRS 1 must be connected to a GMU22, but
installing additional GMU 22 units for other GSU 25 ADAHRS units is optional. An ADAHRS without a
GMU 22 connected will use magnetometer data supplied by other ADAHRS as long as they are both
communicating via CAN.
Table 15-4 Recommended Distance from Magnetic Disturbances
Disturbance Source*
Minimum Distance
from GMU 22
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 [(should 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 other than another GMU 22 (e.g. installed flux
gates, even if unpowered)
2 feet (0.6 meter)
Electrical conductors passing less than 100 mA current [(should be twisted
shielded pair if within 10 feet (3.0 meters)]
1.3 feet (0.4 meter)
*Disturbance sources listed in table do not apply to a second installed GMU 22
