fast, modular wire simulation tools to better understand small wire faults
TRANSCRIPT
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Fast, Modular Wire Simulation Tools to Better Understand
Small Wire Faults
Dr. Cynthia Furse, Brian Jones, Dr.Chit Lo, Eric Lundquist, Dr. Kevin Wheeler, Shang Wu
University of Utah / LiveWire Test Labs / Utah State University/ NASA AMES Research Center
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The Problem
http://www.ksc.nasa.gov/shuttle/missions/sts-67/images/medium/KSC-95EC-0396.jpg
STS-93 Main Engine ControllSpace Shuttle ColumbiaProbable Cause: Mechanical Damage during
maintenance that went undetected until an arc event during launch.
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The Aging Wire Problem
The polymer, Polyimide (Poly-X, Kapton, Stilan, Tefzel) -- chosen because it was a light weight insulator --
breaks down with time
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What Causes Wiring Faults?
Insulation failure3%
Loose connection2%
Short circuit unspecified cause (includes arcing
incidents)3%
Chafed wire insulation leading to short
circuit and/or arcing31%
Other19%
Broken Wires11%
Unspecified Failure6%
Short due to corrosion
1%
Connector Failure9%
Failure due to corrosion
7%
Miswire8%
Source: Navy Safety Center Hazardous Incident Data
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Reflectometry Locates Faults
Time delay between Incident and Reflected Pulses tells distance to fault.
Incident Pulse sent down wire Reflected Pulse comes back
Time delay
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Types of Reflectometry
• Time Domain Reflectometry (TDR)• Frequency Domain Reflectometry (FDR)• Spectral Time Domain Reflectometry (STDR)• Spread Spectrum Time Domain
Reflectometry (SSTDR)• More …
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Correlation Tells Time Shift Between Two Signals
Incident Signal
Reflected SignalTime Shift
Correlation SHIFTS the signals. Multiplies ( x ) them. Integrates ( + ) them.
Distance to Fault (meters) = Time Shift (s) x Velocity (m/s)
STDR:Pseudo Noise (PN)Code
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×
∫PN Code knowntime shift
PN Code unknowntime shift
Spectral Time Domain Reflectometry: STDR
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×
∫Modulated PN codewith knowntime shift
Modulated PN code with unknowntime shift
Spread Spectrum TDR: SSTDR
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MilStd 1553 Plus SSTDR
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Peaks Show Fault
Location of Fault
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But What About Small Faults?
Radial Cracks and Chafes Produce Small Reflections
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Small Fault Small Reflection
Time delay between Incident and Reflected Pulses tells distance to fault.
Incident Pulse sent down wire Reflected Pulse comes back
Time delay
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Load impedances from 20 to 2k ohms
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Load impedances near 50 ohms
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Attenuation Reduces Reflection(frequency dependent)
SSTDR40 ft
Attenuation
How LOW Can You Go??
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Wire Fault Location
• Reflectometry Can Find Faults Dead or Live (Opens/Shorts)
• Finding Small Faults (environmental effects limit detectibility)
• Simulating the System • Damaged Shield Model (promising)
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Predict characteristic Impedance (FDFD, CST)
Forward Response
Experimental
Simulated
TwistedShielded
PairWire
TDR SSTDR FDR
GBD or ABCD?
Simulating Wire Faults
Inversion(Fault Detection
or Location)
Analytical
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Predict characteristic Impedance (FDFD, CST)
Forward Response
Experimental
Simulated
TwistedShielded
PairWire
TDR SSTDR FDR
GBD or ABCD?
Simulating Wire Faults
Inversion(Fault Detection
or Location)
Analytical
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Modular Simulation• Combinations of wire segments• Different Lengths and Impedances• Ideal for Combining ‘Good’ and ‘Bad’ Wires• Must be Frequency Dependent
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Simulate OR Measure Individually
S12
S21
S22S11
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Combine
S12
S21
S22S11
TΓ
TΓ
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Modular Methods Tested
• Time Domain (Generalized Bounce Diagram (GBD), FDTD)
• Frequency Domain (S-parameters, Signal Flow Diagrams, ABCD, modified ABCD)
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ABCD Network Model
S –Parameters ABCD
ABCD ABCD1
2 3
ABCD = ABCD1 x ABCD2 x ABCD3ABCD S-Parameters = (reflection and transmission coefficients)Repeat for All Frequencies IFFT to Time Domain
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Sample Results
0 5 10 15 20 25 30-0.5
0
0.5
1
1.5
Length(m)
Mag
nitu
deL=[3.68, 2.2, 2.77, 3], Z=[50,93,75,50], Load=47pF
MeasuredSimulated - Perfect Step SourceSimulated - Measured Step Source
Figure 52 – A Two-Section ExampleTDR RG58A/U RG59B/URG62/U
2.77m3.68m 2.2m
RG58A/U
3m
C=47pFTDR RG58A/U RG59B/URG62/U
2.77m3.68m 2.2m
RG58A/U
3m
C=47pF
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ABCD Network Model
S –Parameters ABCD
ABCD ABCD1
2 3
Can Be Adapted to Branched NetworksModified ABCD Very Fast and Efficient
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1 1
1 1
A BC D 1V
1I2 2
2 2
A BC D 2V
2I
3V
3In n
n n
A BC D nV
nI
1nV +
1nI +LL
A BC D 1V
1I
1nV +
1nI +1 1 2 2
1 1 2 2
where ... n n
n n
A BA B A BA BC DC D C DC D
=
3 3
3 3
A BC D
2 2
2 2
A BC D
1 1
1 1
A BC D 1V
1I
LZ
2V
2I3V
3I
1 1
1 1
A BC D 1V
1I
shunt
1 01/ 1Z 2V
2I
3V
3I3 3
3 3
A BC D
1 1
1 1
A BC D
1V
1I
2V
2I
2 2
2 2
A BC D
A BC D 1V
1I
2V
2I
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Generalized Bounce DiagramSimulate or Measure Single Sections
a1 b1
a2 b2 a3 b3
a4 b4
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Generalized Bounce DiagramCombine Transmissions and
Reflections
a1 b1
a2 b2 a3 b3
a4 b4
0 0 1 0 0 0 0 00 0 0 0 1 0 0 11 0 0 0 0 0 0 00 0 0 0 1 0 0 00 1 0 1 0 0 0 00 0 0 0 0 0 0 00 0 0 0 0 0 0 00 1 0 0 0 0 0 0
CA
=
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Module 1(10 feet)
Module 2(Fault)
Module 3(7 feet)
Module 4(3 feet)
Module 5(light bulb)
Module 6(5 feet)
Module 7(fan)
“1”“2”
“3”“4”
“5”“6”
“7”“8”
“9”“10”
“13”“14”
“11”“12”
R3 R4
R1 R2
R5 R6
R7 R8
R9 R10
R11 R12
R13 R14
PowerSource Fault
LightBulb
10 feet
fan
7 feet3 feet
5 feet
Can Do Branched Networks
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a1 b1
a2 b2 a3 b3
a4 b4
0 0 1 0 0 0 0 00 0 0 0 1 0 0 11 0 0 0 0 0 0 00 0 0 0 1 0 0 00 1 0 1 0 0 0 00 0 0 0 0 0 0 00 0 0 0 0 0 0 00 1 0 0 0 0 0 0
CA
=
2 1 row or column of 2 row or column of
n C
n C
a n Ab n A
= −=
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Predict characteristic Impedance (FDFD, CST)
Forward Response
Experimental
Simulated
TwistedShielded
PairWire
TDR SSTDR FDR
GBD or ABCD?
GBD or ABCD provide Fast Time Domain Model
Inversion(Fault Detection
or Location)
Analytical
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Predict characteristic Impedance (FDFD, CST)
Forward Response
Experimental
Simulated
TwistedShielded
PairWire
TDR SSTDR FDR
GBD or ABCD?
Simulating Wire Faults
Inversion(Fault Detection
or Location)
Analytical
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Simulating Small Faults2D FDFD 3D FDFD or FEM
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Calculating Impedance
►Cross-section of wire obeys Laplace’s equation
►Numerical equation obtained using central difference method.
This equation is iteratively solved for potential distribution.
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Reference Wire
Test Wire
Electric Potential Distribution
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Reference Wire
Test Wire
Electric Potential Distribution
The Insulation is electrically similar to “air”, and has Very LITTLE effect on Electric Fields
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Removing Insulation has LITTLE Effect on Fields
Insulation damaged on side Insulation damaged on top
Radial crack Insulation damaged on topConductor visible but not damaged
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Magnitude of Reflection
Open and Short Make Large Reflections
Damage to Insulation gives SMALL Reflection
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Magnitude of Reflection
Damaging the Conductor Doesn’t Even Make Much Difference(IF it isn’t touching other Metal)
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Magnitude of Reflection
Putting Water On/Near the Wire DOES matter
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Uncontrolled Impedance Wires
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Effect of Uncontrolled Impedance
Vop = 0.594-0.602c
Controlled Impedance
UnControlled Impedance
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Magnitude of Reflection
Moving the WireMatters Even More
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Magnitude of Reflection
To Prevent False Positives Hardware Must beSet BELOW Normal Variation
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Radial Crack: Why Such a Small Reflection
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What About Chafes?
For Practical Applications, Environment Limits DetectionChafe Detection False Positives
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What About Twisted Shielded Pair?
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Damaged Shield Model
Fields leak out of shield
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Can We Detect These Fields?
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3D CST Simulations
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Damaged Shield
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Field Pattern
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Potential Measurement SystemReceive fields on the outside of shield
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Measurement Example
H Probe
E Probe
Damaged Shield
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Example ResultsConsistent with expected distance. Remaining challenge: Inversion
-20 -15 -10 -5 0 5 10 15 20
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Total length 11.28m, Fault at 8.68m
Distance (m)
Relat
ive A
mplitu
de
Direct contactE-ProbeH-Probe
11.28m2.6m
2.6m
8.68m
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The Role of Bandwidth
• Higher bandwidth– Greater spatial resolution (see smaller length
faults, better resolution of the ones you do see)– Greater loss of high frequencies on the cable
(CABLE limits the possible bandwidth, longer cables have more loss)
– Bandwidth (and specific bands) must be chosen so as not to interfere / be interfered with existing signals
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Types of Reflectometry
• Time Domain Reflectometry (TDR)• Frequency Domain Reflectometry (FDR)• Spectral Time Domain Reflectometry (STDR)• Spread Spectrum Time Domain
Reflectometry (SSTDR)• More …
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Bandwidth: For TDR …
timefrequency
TDR Pulse
timefrequency
A 1/A
A 1/A
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Spread Spectrum
Time
Energy
Time
Energy
Narrow Time– Broader Band
Broad Time – ‘Spread’ over broad frequency band
TDR STDR
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Attenuation Reduces Reflection(frequency dependent)
SSTDR40 ft
Attenuation
Higher Frequency (Bandwidth) = Better Fault Resolution, Shorter Distance
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MilStd 1553 Plus SSTDR
Cannot Interfere With Existing Signals
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• Reflectometry Can Find Faults Dead or Live (Opens/Shorts)
• Finding Small Faults (environmental effects limit detectability)
• Simulating the System • Damaged Shield Model (promising)
Wire Fault Location
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What Next?
• Advanced Interpretation Algorithms• Alternative Reflectometry Methods• Acousto-Optical Correlation• …..
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×
∫Noisewith knowntime shift
Noise with unknowntime shift
Noise Domain Reflectometry (NDR)
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NDR:
• Advantages:• More flexible test method• May utilize existing signals (communication
over power line, etc.)• May provide multi-use of communication
system and testing of the wires in that communication system.
• Disadvantages:• SNR not as good as S/SSTDR (requires
longer test / averaging time)
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Electrical Correlation Today
Slow, one delayintegrated at a time
A B
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Acousto-Optical Correlation:Parallel Integration
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Acousto-Optic DeviceExample of AO Deflector (Courtesy of Crystal Technology)
Sound field inside
typical AO device
=
= −−
l
aaB nv
cK
kωω
θ2
sin2
sin 11
DetectLocation ofDiffractedBeam(lens/CCD)
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Acousto Optic Correlator
Acousto-optic Interaction
Light source
At Bragg angle
Transducer with PN code modulation
Principal diffracted beam
Detected with
An Imaging Lens and CCD
Undiffracted beam
Individual delays implemented in parallelτ1τ2τ3
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Example Measured CCD Output
CCD Pixel #
Magnitude
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Distance to Fault
0
50
100
150
200
250
300
350
400
450
500
0 100 200 300 400 500 600 700
length of the wire (ft)
peak
pos
ition
(pix
e
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• Reflectometry Can Find Faults Dead or Live (Opens/Shorts)
• Finding Small Faults (environmental effects limit detectibility)
• Simulating the System • Damaged Shield Model (promising)• In the Future ….
– Advanced Interpretive Algorithms (Inversion)– Acousto-Optic Correlator (speed and power)
Wire Fault Location
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Thank you to NASA AMES Research Center for
Sponsoring this Research