fast, modular wire simulation tools to better understand small wire faults

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

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.

http://www.ksc.nasa.gov/shuttle/missions/sts-67/�

The Aging Wire Problem

The polymer, Polyimide (Poly-X, Kapton, Stilan, Tefzel) -- chosen because it was a light weight insulator --

breaks down with time

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

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

Types of Reflectometry

• Time Domain Reflectometry (TDR)• Frequency Domain Reflectometry (FDR)• Spectral Time Domain Reflectometry (STDR)• Spread Spectrum Time Domain

Reflectometry (SSTDR)• More …

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

×

∫PN Code knowntime shift

PN Code unknowntime shift

Spectral Time Domain Reflectometry: STDR

×

∫Modulated PN codewith knowntime shift

Modulated PN code with unknowntime shift

Spread Spectrum TDR: SSTDR

MilStd 1553 Plus SSTDR

Peaks Show Fault

Location of Fault

But What About Small Faults?

Radial Cracks and Chafes Produce Small Reflections

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

Load impedances from 20 to 2k ohms

Load impedances near 50 ohms

Attenuation Reduces Reflection(frequency dependent)

SSTDR40 ft

Attenuation

How LOW Can You Go??

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)

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

Modular Simulation• Combinations of wire segments• Different Lengths and Impedances• Ideal for Combining ‘Good’ and ‘Bad’ Wires• Must be Frequency Dependent

Simulate OR Measure Individually

S12

S21

S22S11

Combine

S12

S21

S22S11

TΓ

TΓ

Modular Methods Tested

• Time Domain (Generalized Bounce Diagram (GBD), FDTD)

• Frequency Domain (S-parameters, Signal Flow Diagrams, ABCD, modified ABCD)

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

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

ABCD Network Model

S –Parameters ABCD

ABCD ABCD1

2 3

Can Be Adapted to Branched NetworksModified ABCD Very Fast and Efficient

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

Generalized Bounce DiagramSimulate or Measure Single Sections

a1 b1

a2 b2 a3 b3

a4 b4

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

=

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

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

= −=


Forward Response

Experimental

Simulated

TwistedShielded

PairWire

TDR SSTDR FDR

GBD or ABCD?

GBD or ABCD provide Fast Time Domain Model


or Location)

Analytical


Forward Response

Experimental

Simulated

TwistedShielded

PairWire

TDR SSTDR FDR

GBD or ABCD?

Simulating Wire Faults


or Location)

Analytical

Simulating Small Faults2D FDFD 3D FDFD or FEM

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.

Reference Wire

Test Wire

Electric Potential Distribution

Reference Wire

Test Wire

Electric Potential Distribution

The Insulation is electrically similar to “air”, and has Very LITTLE effect on Electric Fields

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

Magnitude of Reflection

Open and Short Make Large Reflections

Damage to Insulation gives SMALL Reflection


Damaging the Conductor Doesn’t Even Make Much Difference(IF it isn’t touching other Metal)


Putting Water On/Near the Wire DOES matter

Uncontrolled Impedance Wires

Effect of Uncontrolled Impedance

Vop = 0.594-0.602c

Controlled Impedance

UnControlled Impedance


Moving the WireMatters Even More


To Prevent False Positives Hardware Must beSet BELOW Normal Variation

Radial Crack: Why Such a Small Reflection

What About Chafes?

For Practical Applications, Environment Limits DetectionChafe Detection False Positives

What About Twisted Shielded Pair?

Damaged Shield Model

Fields leak out of shield

Can We Detect These Fields?

3D CST Simulations

Damaged Shield

Field Pattern

Potential Measurement SystemReceive fields on the outside of shield

Measurement Example

H Probe

E Probe

Damaged Shield

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

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

Types of Reflectometry

• Time Domain Reflectometry (TDR)• Frequency Domain Reflectometry (FDR)• Spectral Time Domain Reflectometry (STDR)• Spread Spectrum Time Domain

Reflectometry (SSTDR)• More …

Bandwidth: For TDR …

timefrequency

TDR Pulse

timefrequency

A 1/A

A 1/A

Spread Spectrum

Time

Energy

Time

Energy

Narrow Time– Broader Band

Broad Time – ‘Spread’ over broad frequency band

TDR STDR

Attenuation Reduces Reflection(frequency dependent)

SSTDR40 ft

Attenuation

Higher Frequency (Bandwidth) = Better Fault Resolution, Shorter Distance

MilStd 1553 Plus SSTDR

Cannot Interfere With Existing Signals


• Finding Small Faults (environmental effects limit detectability)

• Simulating the System • Damaged Shield Model (promising)

Wire Fault Location

What Next?

• Advanced Interpretation Algorithms• Alternative Reflectometry Methods• Acousto-Optical Correlation• …..

×

∫Noisewith knowntime shift

Noise with unknowntime shift

Noise Domain Reflectometry (NDR)

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)

Electrical Correlation Today

Slow, one delayintegrated at a time

A B

Acousto-Optical Correlation:Parallel Integration

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)

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

Example Measured CCD Output

CCD Pixel #

Magnitude

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


• 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

Thank you to NASA AMES Research Center for

Sponsoring this Research

Questions?

Dr. Cynthia [email protected]

fast, modular wire simulation tools to better understand small wire faults

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