Presentazione di PowerPoint hazards on... · 2014-03-13 · • La presenza del terreno •...
Transcript of Presentazione di PowerPoint hazards on... · 2014-03-13 · • La presenza del terreno •...
Rischi elettromagnetici a bordo
di aeromobili
Corso di Elettrotecnica V.O.
Corso di Laurea di Ingegneria Aerospaziale
a.a. 2001-2002
Prof. M.S. Sarto
• Interferenze con dispositivi elettronici
portatili
• Invecchiamento dei cablaggi
• Effetti indiretti della fulminazione
diretta ed indiretta di aeromobili
• Interferenze con campi elettromagnetici
di elevata intensità (HIRF)
Interferenze con dispositivi elettronici
portatili
Esempi di dispositivi elettronici portatili sono:
• Cell phones
• Laptop computers
• Portable AM/FM Radio Cassette Players
• Portable CD Players
• Electronic Games
• HF Radio
Prove di EMI prodotte da PEDs su aeromobili a terra
sono scarsamente significative:
Le condizioni di prova a terra e di volo sono
completamente diverse a causa di numerosi fattori:
• La presenza del terreno
• L’assenza delle persone
• La forte dipendenza del manifestarsi dell’EMI dai
fenomeni di risonanza elettromagnetica che si
presentano a bordo
• Non si riesce a ricreare le stesse condizioni di EMI a
terra
Posizionamento delle antenne su un AIRBUS 320
Possibili modalità di accoppiamento del disturbo
elettromagnetico prodotto da PEDs su un aeromobile
• US Federal Aviation Regulation 91.21 prohibits the
use of any portable electronic devices on board
aircraft, with the exception of voice recorders, hearing
aids, heart pacemakers, shavers, and any other device
that the operator of the aircraft has determined will not
cause interference with the navigation or
communication systems of its aircraft
• The regulation puts the responsibility firmly on an
individual airline to determine that there is no
interference.
• US airlines implement a general ban on using any
portable electronic devices (PEDs) below 10,000ft
Normative che regolano l’uso dei PEDs a bordo di
aeromobili
Interferenze elettromagnetiche prodotte
dall’uso di telefoni cellulari
Cellular phones are a particular source of problems
because, regardless of whether they may interfere with
aircraft systems, the technology on which cellular
telephones are based precludes their effective use on
aircraft.
This applies to all cellular phones, including the analogue
technology in the US and the digital GSM technology in
Europe.
The technology of cellular phones is based on small local ground-
based reception areas called `cells'. A cellphone user is served by just
one cell, and when reaching the boundary of a cell, will be `handed
over' to another cell which (s)he is about to enter. The topology of
coverage is based on the assumption that the user is on or near the
ground, and it is a technical assumption on which the entire system is
based that a user will be within `sight' of just one cell except when
nearing a cell boundary.
When in an aircraft, however, a user is within radio `sight' of many
cells, simply because (s)he is way off the ground. An attempted call or
reception from an aircraft would activate many if not all cells in the
local area, which `breaks' the technology -- it causes many
transmission problems and the system is disturbed. Therefore the
various communication authorities, such as the US Federal
Communications Commission (FCC), ban the attempted use of
cellular phones while on board aircraft.
Nordwall reports that the RTCA Committee 177 inquiry
found 137 `incidents' (pilot reports, anecdotes) reported
either to them, or to the FAA/NASA Aviation Safety
Reporting System (ASRS) program, or to the International
Air Transport Association (IATA).
VOR reception was affected in 111 incidents -- by far the
most common occurrence.
From the 33 reports direct to RTCA, 21 incidents related
to laptop computers and only 2 to cellular phones.
Navigation systems were affected in 26 of those
incidents; fuel systems, warning lights and propulsion
reported one incident each.
Rough correlation of suspect with effect by turning the
suspect device on and off was found in 14 cases, on-off-on
in 6 cases, and no correlation in 13 cases.
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Signal intensity [dB]
Numero di eventi di EMI prodotta da cellulari
nelle diverse fasi di volo
GSM filed signals drops
to 0 above 3.000 m
Frequenza del numero di eventi per volo
2
7%
3
10%
4
4%
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6% >5
0%
1
73%
Invecchiamento dei cablaggi
Wiring integrity and safety issues have emerged as a
major aerospace problem associated with the loss of
SwissAir 111 and TWA 800.
Wiring is the nervous system of every electronic system.
Wiring problems have been known to cause loss of
signals, system shutdowns, smoke, fires and
explosions.
In lesser forms, wiring problems cause millions of dollars in
troubleshooting and maintenance. Modern technology
provides a viable solution.
Electrical Wiring Problems
Electrical wiring is usually not a significant problem in new
aircraft, because designers specify a life of over eighteen
years (which is the expected life of the aircraft).
Wiring normally easily lasts the design service life, say 20
years. As systems near the design service life wiring
becomes a major cost driver. Many aircraft are refurbished
and overhauled to stay in service for thirty or more years.
At the Aging Aircraft Conference 2000 the Air Force stated
that it takes 18 months to rewire a C130 aircraft. Because of
the huge cost, and time, wiring is usually not replaced.
Some wiring problems are caused by build up of corrosion
on exposed metal wire surfaces and loosening of connector
pins due to repeated opening of connectors. Other problems
come from abuse during maintenance.
NASA experienced a shutdown of space shuttles due to
rubbing against a sharp screw.
The onboard network is constituted by nearly 12-17
thousands of wires, grouped in 300-500 bundles.
There are: single-core and multi-core shielded and
unshielded cables, data-bus and coaxial cables are.
Cables are classified according their EMC category:
E : emitting
S: susceptible
P: power
R: radio-audio
D: data-bus
Cable bundles of different category running along the same
route are collected to form complex harnesses enclosed or
not in overall screen or in dielectric sheath.
The cable bundle configurations are extremely variable, and
are installed inside the aircraft. Nearly 25 different installation
typologies are schematized.
Examples of complex bundles
Troubleshooting Wiring Problems
Trouble shooting Wiring is a maintainer’s worst nightmare.
It is not unusual to take several hours to find intermittent
shorts and opens in aircraft wiring.
The process usually requires a cart full of electronic
equipment, extensive traning and years of on the job
experience.
Records in 1988 show that Navy maintainers spent over
240,000 hours troubleshooting wiring problems for the
fleet of F14 aircraft.
Wiring problems are known to be a significant portion of
aircraft maintenance costs.
Safety Concerns
Shorts, arcing, opens circuits, or intermittent problems are
a real flight safety concern.
Sandia National Laboratory scientists have shown that
build up of sulfur on wiring from immersion in jet fuel could
have ignited the fuel tank vapors in the Trans World Airlines
800 disaster.
The Navy has a special team working on use of inert gases
to put out fires caused by wiring arc tracking. Open circuits
or arcing can result in inadvertent mid-air actuation of flaps
or retracted landing gear.
The spurious signals also present a major problem in
diagnosing whether a system is failed or the wiring is
deteriorated causing spurious signal conditions.
Sviluppo di tecniche di diagnostica
per individuare la presenza di
guasti e difetti sui cablaggi a
bordo di aeromobili
The FAA’s Aging Aircraft Systems responds to a February 1997
recommendation by the White House Commission on Aviation
Safety and Security, chared by Vice President Al Gore.
“The White House Commission specifically recommended that the
FAA work in cooperation with airlines and manufacturers to expand
the FAA’s aging aircraft program to include a variety of systems”,
e.g. “electrical wiring, connectors, wiring harnesses, and cables”.
(Washington D.C. 10.01.98)
FAA “Aging Transport Systems Rulemaking Advisory
Committee” (ATSRAC) - Wiring Group: wire diagnostics, smart
wire, arc fault circuit breakers.
IL TEMA DI RICERCA A LIVELLO
INTERNAZIONALE
Il National Transportation Safety Board (NTSB) degli
Stati Uniti raccomanda lo sviluppo di nuove
tecnologie che consentano la diagnostica continua
dello stato di “salute” del cablaggio e cioè durante il
volo e non solo come attualmente avviene nelle
operazioni di manutenzione.
Prove a bordo
dell’Airbus 321 Alitalia
Notes: O=Open; S=Short; D=Defect
Conductor AWG Cable Test
or Size Jacket/Sheath Impedance Application (*)
Basic Cores (ohm)
Nickel Plated Copper
Spiral Shield
Nickel Plated Copper
Spiral Shield
ShieldType
SJ 1 CF 22
SJ 20
/
/1 CF
Insulation
/
/
PI Tape+FEP
PI Tape+FEP
O/S
O/S
Airframe Wiring
Airframe Wiring
Only the use of the portable scalar analyser is possible
The choice of the central frequency and span is critical
Pannello
Cabina Vano Bagagli
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m
db
SJ22
(12,45 m)
Fmax=106 MHz
Fmax=164 MHz
-43 dB
-22 dB
Alitalia Airbus 321
Cable no.1
Cable no.2
Open ended cable no.1
-80
-60
-40
-20
0
0 5 10 15 20 25
Distance [m]
Refl
ecti
on
co
eff
. [d
B]
Effective distance from OE termination: 10 m
Measured distance from OE termination: 9.72 m
Central Frequency = 36.16 MHz
Span = 137.28 MHz
Open ended cable no.2
-80
-60
-40
-20
0
0 5 10 15 20 25 30 35
Distance [m]
Re
fle
cti
on
co
eff
. [d
B]
Effective distance from OE termination: 14.5 m
Measured distance from OE termination: 14.65 m
Central Frequency = 10 MHz
Span = 163.45 MHz
Alitalia Airbus 321
Cable no.3 Cable no.4
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-60
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Distance [m]
Refl
ecti
on
co
eff
. [d
B]
Open ended cable no.3
Effective distance from OE termination: 18 m
Measured distance from OE termination: 17.91 m
Central Frequency = 10 MHz
Span = 73.2 MHz
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Distance [m]
Refl
ecti
on
co
eff
. [d
B]
Open ended cable no.4
Effective distance from OE termination: 18.8 m
Measured distance from OE termination: 18.67 m
Central Frequency = 10 MHz
Span = 73.2 MHz
Critical aspects
• Testing of cable sections with interconnection connectors
• Testing of single core unshielded cables
• Effect of the bundle on the cable under test
• Use of the reference return cable
• Use of the reference measurement of the undamaged cable
• Post processing of the measured data for fault location
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m
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disconnessi connessi
R&S FSH3:
Frequenza Centrale= 58 MHz
Span = 96 MHz
SJ20(8,12m) SJ20(10,68m)
SET-UP VNA
Modalità Low Pass Step
Formato Real
CARATTERISTICHE DEL CAVO (tripolare non schermato)
Lunghezza totale 1,385 m
Distanza dal guasto 0,93 m
Vf 0,828
MISURE ESEGUITE
X0 Cavo integro
X1 2 mm di guaina
X2 2 mm di schermo
X3 4 mm di schermo
Coefficiente di Autocorrelazione
N° di punti dell’intervallo 80
Ritardo temporale τ 2
Coefficiente di Correlazione Statistica
N° di punti dell’intervallo 200
Prove di laboratorio su cavo JN1018 SK 004
Prove di laboratorio su cavo JN1018 SK 004
Misure Riflettometriche
Postprocessing delle misure riflettometriche
Prove di laboratorio su cavo JN1018 SK 004
Risultato delle elaborazioni statistiche in funzione degli obiettivi proposti
Prove di laboratorio su cavo JN1019 SK 004
SET-UP VNA
Modalità Low Pass Step
Formato Real
CARATTERISTICHE DEL CAVO (tripolare schermato)
Lunghezza totale 1,82 m
Distanza dal guasto 1 0,54 m
Distanza dal guasto 2 1,045 m
Vf 0,741
MISURE ESEGUITE
X0 Misura di riferimento
X1 Misura con i due guasti
Coefficiente di Autocorrelazione
N° di punti
dell’intervallo
100
Ritardo temporale τ 2
Coefficiente di Correlazione Statistica
N° di punti
dell’intervallo
250
Prove di laboratorio su cavo JN1019 SK 004
guasto 1 guasto 2
Misure RiflettometrichePostprocessing delle misure riflettometriche
Prove di laboratorio su cavo JN1019 SK 004
Risultato delle elaborazioni statistiche in funzione degli obiettivi proposti
Prove di laboratorio su cavo JN1018 SK 004
SET-UP VNA
Modalità Low Pass Impulse
Formato Log Mag
CARATTERISTICHE DEL CAVO (tripolare non schermato)
Lunghezza totale 1,385 m
Distanza dal guasto 0,93 m
Vf 0,828
MISURE ESEGUITE
X0 Cavo integro
X1 2 mm di guaina
X2 2 mm di schermo
X3 4 mm di schermo
Coefficiente di Autocorrelazione
N° di punti dell’intervallo 300
Ritardo temporale τ 4
Coefficiente di Correlazione Statistica
N° di punti dell’intervallo 250
Prove di laboratorio su cavo JN1018 SK 004
Misure Riflettometriche
Postprocessing delle misure riflettometriche
Prove di laboratorio su cavo JN1018 SK 004
Risultato delle elaborazioni statistiche in funzione degli obiettivi proposti
SET-UP VNA
Frequency range 30 kHz- 1000 MHz
CABLE CHARACTERISTICS
Total length 2,80 m
Distance from fault 1,2 m
Velcity factor 0,72
Propagation time to
fault
12 nS
Cable under test:
(M22759/3416)diametro int.:1,3 mm ; diametro est.:2 mm
;
Reference return cable:
(48T10C01G020)diametro int.:1mm ; diametro est.:1,4 mm
;
TESTS PERFORMED
x0 Undamaged cable
x1 30% of cable section broken
x2 50% of cable section broken
x3 80% of cable section broken
Single core unshielded cable inside a cable bundle with
reference return cable
0 5 10 15 20 25 30-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6Misure
tempo [nS]
coeff. riflessio
ne
x0x1x2x3
8 9 10 11 12 13 14 15 16
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
Misure
tempo [nS]
coeff. riflessio
ne
x0x1x2x3
cable end
Measurement
Difference with respect to the reference
measurement of the undamaged cable
0 5 10 15 20 25 30-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04Differenza tra le misure
tempo [nS]
coeff. corr
ela
zio
ne
(x1-x0)(x2-x0)(x3-x0)
fault
Post processing of the difference with respect to the reference measurement of
the undamaged cable
0 5 10 15 20 25 30-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8(Differenza*Correlazione) tra le misure
tempo [nS]
corr
ela
zio
ne m
odific
ata
(x1-x0)(x2-x0)(x3-x0)
Fault
localization
post
pro
cess
ed d
ata
fault localization at 12 ns !