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The T-HUMS uses condition indicators based on several transforms, in-cluding
DFTs,
Ceptrum
and
periodograms
from
non-averaged
signals
[21].
Indicators are then normalized against learnt baselines to representing the normal state aircraft speci.c vibration signature. The system then compen-sates for environmental changes using a polynomial approximation of the relationship between vibration signature and environmental conditions. It also applies trend analysis based on linear regression both on condition in-dicators, thus creating new indicators, and on classi.cation results. This is done using two frame sizes, detecting long and short term tendency. The indicators are then subject to further processing by classi.cation algorithms such as cluster systems, fuzzy logic, and arti.cial neural networks.

3.6 M’ARMS and EuroARMS
Eurocopter is currently supporting two HUMS; Modular Aircraft Recording and Monitoring System (M’ARMS), and its predecessor Eurocopter Aircraft Recording and Monitoring System (EuroARMS). Although EuroARMS and M’ARMS are two di.erent systems, they inhibit the same functions. Thus, these two systems are in this report jointly referred to as Aircraft Recording and Monitoring System (ARMS). Both systems collect data while in oper-ation, which are downloaded to a PCMCIA .ash memory card after each .ight
(Fig.
3.4).
The
content
of
the
.ash
card
is
analyzed
at
a
Windows
NT
or Server 2003 workstation using specialized software. This workstation is referred to as the ground station.
3.6.1 Airborne Segment
The ARMS airborne segment taps into the Arinc databus, which is used for transmitting data between di.erent system modules. This provides access to contextual information such as altitude, temperature and air speed. Contex-tual information is used for generating parameter threshold overshoot alarms and estimating component load cycles. Further, this information is used for determining if the aircraft is in a .ight stage when it is possible to perform vibration acquisitions.

In addition to using data acquired through the Arinc bus, the ARMS has its own set of sensors. This includes speed sensors mounted on the engine compressors, engine turbines, main rotor and tail rotor, as well as a number of accelerometers. The number of accelerometers is aircraft speci.c, but does generally cover engines, all gearboxes, oil cooler, rotors and the tail drive shaft.
During one acquisition cycle, the system acquires .nite length acquisitions from all monitored components, following a preset program. A total of six acquisition cycles are performed per .ight; one on the ground, and .ve in cruise
(Fig.
3.5).
To
save
space,
acquisitions
are
immediately
re-sampled
and
averaged with the shaft rotation speed. This shortens gear, shaft and rotor acquisitions from 200 rotations to simply 1. Vibration signals, parameter exceedance alarms and load cycle calculations are stored on a data cartridge at the end of the .ight. The cartridge is then analyzed at the ground station.
　
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