Display Sensors; Table 4-5 Gmu Recommended Distance From Sources Of Magnetic Interference; Gmu 11/44B - Garmin GI 275 Installation Manual

4.6 Display Sensors

Display sensors consist of GMU 11/44B Magnetometers and GTP 59 OAT Probe. When installed in a
metallic aircraft, the display sensors must be electrically bonded to a nearby metallic structure, with the
exception of the GMU 11 when overbraid is not required. Resistance must be in accordance with
Section 4.3 with the connector disconnected. When installed in a non-metallic aircraft, the display sensors
and display sensor connectors must be separated from any electrically conductive components by a
minimum of 0.5 inches. Non-conductive doublers or barriers may be required to isolate the sensors.
4.6.1

GMU 11/44B

The GMU 11 and GMU 44B are very sensitive magnetic sensors. Before they are installed, their location
must be surveyed to verify that they pass a Magnetic Interference Test (refer to Section 4.6.1.1). Follow the
GMU separation guidelines presented in Table 4-5 when selecting an acceptable location. For aircraft
model-specific GMU 11/44B installation requirements, refer to Appendix D.
NOTE
For metal and tube-and-fabric aircraft, the GMU must be electrically bonded to the
aircraft metallic structure that forms the ground plane, with the exception of the GMU 11
when overbraid is not required.
NOTE
For composite aircraft, the GMU 11/44B must not be electrically bonded to the aircraft
ground plane. If the structure is conductive at the mounting location, provisions must be
made to electrically isolate the GMU from the conductive structure per instructions in this
section.
CAUTION
A Magnetic Interference Survey must be successfully accomplished for locations in which
a flux valve or flux gate was previously installed, as it may not be adequate for the GMU.

Table 4-5 GMU Recommended Distance from Sources of Magnetic Interference

1. Electric relays and motors, including servo motors
2. Ferromagnetic (i.e., iron, steel, or cobalt materials) mass heavier than 1 kg
(e.g. landing gear)
3. Ferromagnetic mass less than 1 kg total (e.g., control cables)
4. Electrical devices that draw a current of more than 100 mA
5. Electrical conductors that pass a current of more than 100 mA
6. Electrical devices that draw a current of less than 100 mA
7. Magnetic measuring device other than another GMU (e.g., existing flux gate, even
if not powered)
8. Electrical conductors passing less than 100 mA current
190-02246-10
Rev. 11
Source of Magnetic Interference
In Order of Importance
GI 275 Part 23 AML STC Installation Manual
Min. Distance
feet [meters]
10.0 [3.0]
8.2 [2.5]
3.0 [1.0]
3.0 [1.0]
3.0 [1.0]
2.0 [0.6]
2.0 [0.6]
1.3 [0.4]
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