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Identification of Aging Aircraft Electrical Wiring
Woolrich Engineering Consulting Firm
Midterm Report
Group Members: Robert Beremand – Project Manager Chad Hanak – Senior Engineer Melissa Straubel – Senior Engineer
Sponsors: Dr. R. O. Stearman Marcus Scott Kruger
March 7, 2003
Woolrich Engineering Consulting Firm Austin, TX 78705
March 7, 2003 Dr. R.O. Stearman Department of Aerospace Engineering and Engineering Mechanics College of Engineering, University of Texas at Austin Dear Sir: The attached report contains a description of Woolrich Engineering Consulting Firm’s efforts in evaluating wire aging experiments and the effect of aging on the triboelectric effect. Within the report are background information, theory, a description of the experimental setup and laboratory specimen, a list of work that WECF still needs to complete, and a description of the cost analysis. The background information discusses the history of the problem, recommended solutions to the problem, and also presents technical background including the types of wire failures. A description of the triboelectric effect and frequency response are presented in the theory portion of the report. In subsequent sections, descriptions of the wire to be used in our experiments, as well as an explanation of the test setup, are discussed. While we have yet to simulate the aging of the wires, WECF was successful in obtaining wire, an incubator and a freezer, and evaluating the test setup. The attached report contains the first half semester’s work; however, if you have any questions/comments, please feel free to contact us via email at [email protected]. Sincerely, Melissa Straubel Robert Beremand Chad Hanak Senior Engineer Project Manager Senior Engineer
i
Abstract
The analysis techniques and results developed in this paper were motivated by a need to find a viable method of determining the quality of aircraft electrical wiring. Deteriorating insulation on electrical wiring is considered a significant safety hazard in aviation. An aircraft’s wiring cannot be visually inspected without disassembling the craft, which is not a feasible option. Therefore, an indirect method of gauging the condition of a wire’s insulation is required. This study builds upon the research of previous studies by attempting to use the triboelectric effect in wiring to determine the condition of the wire. The authors hope to find that a wire excited by a vibration of know frequency and amplitude will produce a predictable triboelectric response that varies with the condition of the wire.
Wire specimen aging techniques from previous studies were evaluated and modified to yield better (faster) results. A freezer and an incubator have been acquired for this purpose, but are not yet operational. Consistency problems with the wire analysis test setup used by previous studies have also been addressed, and solutions proposed. Particular attention has been given to reducing the Electro-Magnetic Interference (EMI) between various testing components. The direction of future work has also been noted.
ii
Acknowledgements
WECF would like to thank our sponsors for this project, Dr. R.O. Stearman and
Marcus Kruger. Dr. Stearman, who is an aerospace engineering professor at the
University of Texas at Austin, has been instrumental in acquiring several major
components for this project. These components include an incubator in which we will
conduct our heat and humidity tests and a freezer in which we will conduct our cold tests.
He has also used personal contacts to assist us in obtaining actual aged wire from an
aviation scrap yard in Dallas. Marcus Kruger, an aerospace engineering graduate student,
has provided his knowledge and guidance in the setup of this project. WECF has met
with him during weekly consultation sessions in which we analyzed the experimental
setup and methods for testing.
WECF would also like to thank Frank Wise, the onsite electrician for the
Aerospace Engineering and Engineering Mechanics Department. He offered his
expertise to assist us in researching and obtaining the wire we will be using in our
experiments.
Without the contributions of these individuals, the work conducted by WECF
would have been incredibly difficult and time consuming.
iii
Table of Contents
Abstract............................................................................................................................... i Acknowledgements ........................................................................................................... ii List of Tables and Figures ............................................................................................... iv 1.0 Introduction........................................................................................................... 1
1.1 Previous Work................................................................................................... 1 1.2 Methodology ...................................................................................................... 2 1.3 Project Scope ..................................................................................................... 4 1.4 Report Overview ............................................................................................... 4 2.1 Types of Wire Failures ..................................................................................... 6 2.2 Current Methods Used to Detect Faulty Wiring............................................ 6
3.0 Theory .................................................................................................................... 7 3.1 Triboelectric Effect ........................................................................................... 7 3.2 Frequency Response ......................................................................................... 9
4.0 Laboratory Specimen ......................................................................................... 10 4.1 Wire Selection.................................................................................................. 10
5.0 Phase I: Laboratory Aging................................................................................. 12 5.1 Data Collection Cycle ..................................................................................... 12 5.2 Aging Processes ............................................................................................. 13 5.3 Aging Equipment ............................................................................................ 16 5.4 Anticipated Results ......................................................................................... 17
6.0 Age Analysis ........................................................................................................ 19 6.1 Experimental Setup ........................................................................................ 19
6.1.1 Signal Analyzer/Computer........................................................................ 19 6.1.2 Data Acquisition System........................................................................... 20 6.1.3 Amplifier................................................................................................... 20 6.1.4 Electromagnetic Shaker ............................................................................ 21 6.1.5 Electromagnetic Interference (EMI) Reduction........................................ 21
6.2 Anticipated Results ......................................................................................... 22 7.0 Work to be Completed........................................................................................ 26
7.1 Acquisitions ..................................................................................................... 26 7.2 Preparation of Experimental Setup .............................................................. 27 7.3 Verification and Testing ................................................................................. 27
8.0 Task Distributions............................................................................................... 28 9.0 Cost Analysis ....................................................................................................... 29 10.0 Conclusion ........................................................................................................... 30 11.0 Works Cited......................................................................................................... 31 12.0 Appendix – Timeline........................................................................................... 32
iv
List of Tables and Figures Figure 1: Wreckage from TWA Flight 800 [3]
Figure 2: Relative movement between insulating and conducting surfaces induces a
current [5]
Figure 3: Alpha Wire Spools
Figure 4: Data Collection Cycle Comparison
Figure 5: Aged Wire Samples [4]
Figure 6: Freezer Donated by UT-Austin Zoology Department
Figure 7: Signal Analyzer, Amplifier, and shaker [4] Figure 8: Wire/Electromagnetic Shaker System
Figure 9: Differences in Redox Reaction Rates Can Create an Electric Potential Between
Two Materials [7]
Figure 10: Diagram labeling the distribution of tasks
Table 1: Wire Specifications [8]
1
1.0 Introduction
Since the 1980s, the Navy and Air Force have documented problems with aircraft
electrical wires exposed to prolonged high heat, moisture, chemicals, and vibration
during aircraft operation. Faulty electrical wire insulation has caused in-flight fires and
electrical failures in addition to control connection failures. This has caused
malfunctions in aircraft spoilers, and has triggered inadvertent autopilot commands, or
disabled the autopilot completely [1].
Similar problems have occurred in the commercial airplane industry. More than
half of the world’s passenger jets contain potentially problematic wire insulation [2].
Two high profile crashes, TWA Flight 800 and Swiss Air Flight 111, were blamed on
faulty electrical wiring.
Figure 1: Wreckage from TWA Flight 800 [3]
1.1 Previous Work
The fall 2002 group performed laboratory aging tests on Alpha 1632 wire
specimens. From the laboratory aging results, the previous group concluded that heat and
humidity tests did not properly age the wire specimens. Visual and touch inspections of
wires aged over 7 ½ weeks showed no changes in the wire’s physical characteristics. The
2
group felt that this result was due its inability to increase the temperature imposed upon
the wire specimens above 120°F [4]. The group also felt that the laboratory aging
experiments would be more affective if conducted over a longer amount of time.
Another test was performed by the fall 2002 group in which they exposed the
Alpha wire to saltwater and Jet-A fuel. They concluded that the saltwater and Jet-A fuel
tests successfully simulated the aging of the wire. Visual inspection of wire subjected to
a saltwater solution showed corrosion that tarnished the wire and bonded the copper
strands together. Physically handling the wire revealed that was noticeably more brittle.
Visual inspection of wire submerged in Jet-A Fuel showed that the rubber insulation had
expanded in diameter and length [4].
In the age analysis portion of the group’s project, they were unsuccessful in
identifying a relationship between the aged wire and its triboelectric response. Single
frequency tests were performed on the aged wires, but no trend could be determined from
data points that were taken. The group suspected the inaccurate data were due to
electromagnetic interference attributed to the electromagnetic shaker because of its
proximity to the wire circuit [4].
1.2 Methodology
This study attempts to build on the work of previous design groups who have
examined this problem. In particular, three tasks are being given a great deal of attention:
• Redesigning and validating the age analysis laboratory setup
• Enhancing the thermal wire aging technique and setup
• Searching for qualitative evidence that the triboelectric response of a wire deteriorates
with age by analyzing documented wires collected from aviation scrap yards.
3
Previous design groups, notably BSS Engineering Inc. (the fall 2002 group), reported that
the current age analysis laboratory setup is not capable of consistently reproducing a
characteristic triboelectric response from a nominal piece of wire [4]. Without the
capability to reproduce nominal results in a controlled test setup, the testing of actual
aged wire specimens is of no real value. Thus, it is important for WECF to first modify
and validate the laboratory analysis setup before attempting to generate any triboelectric
response data.
Another difficulty encountered by previous design groups involved the thermal
aging technique employed to deteriorate the wires’ insulation. Past thermal aging
techniques involved placing wires in an environmental chamber in Ernest Cockrell, Jr.
Hall, which is under the administration of the Civil Engineering Department at the
University of Texas at Austin [4]. This technique proved to be ineffective, however,
because ongoing civil engineering experiments that also resided in the chamber required
a constant temperature of 120°F [4]. Such a temperature is well within the operating
range of the wire insulation, and, therefore, did little to deteriorate the insulation over the
7 ½ week duration of the study. In order to more effectively thermally age the wire
specimens, WECF decided it was necessary to obtain their own equipment. This will
remove the constraints that kept the previous design group from successfully thermally
aging their wire specimens.
The technique WECF plans to use to thermally age the wire was a thermal cycling
process. Wire specimens will be placed in the environmental chamber and subjected to a
temperature of 170°F. After 24 hours of heat, the specimens were removed from the
chamber and placed in a freezer for 24 hours. The cycle will then repeat for the duration
of the study. Other aging techniques employed by WECF will be identical to those
4
employed by BSS Engineering Inc. One set of wire specimens was soaked in salt water,
and another set was soaked in Jet-A fuel. These techniques were proven to be effective
by BSS Engineering Inc., and, therefore, will be repeated by WECF.
Finally, WECF decided to use wire that had seen years of service in actual
aircrafts to search for qualitative evidence that the triboelectric response of a wire
changes as the wire ages. The limited amount of time in which this study had to be
conducted meant that it would be possible to age wire specimens by only a small amount.
The controlled aging techniques, however, will allow WECF to search for a quantitative
trend that defines the change in the triboelectric response of a wire with time. Since this
result is not at all apparent at present, it was deemed prudent to collect documented wires
of various ages from an aviation scrap yard and analyze their triboelectric responses to
see if a qualitative trend could indeed be observed.
1.3 Project Scope
This report presents the theory behind the triboelectric effect that motivated this
study. The results of previous design groups, and their effects on current undertakings,
are also discussed. All modifications to the previous laboratory analysis setup and aging
techniques are noted in detail. The report culminates with the results and conclusions
arrived at by WECF. Finally, recommendations for further investigations into wire age
analysis are presented.
1.4 Report Overview
In the following sections of this report, WECF will explain the technical
background and theory behind this project, describe the wire we have chosen to use in
5
our experiments, and give technical details of the wire aging techniques and experimental
setup. We will also provide a list of the work we plan to complete in the second half of
the semester, as well as a description of the costs we have encountered thus far.
6
2.0 Technical Background
2.1 Types of Wire Failures
When wires deteriorate, the insulation can begin to chaff and crack. This may be
a result of prolonged exposure to harsh temperature, humidity, corrosion, and/or vibration.
Kapton wire appears to be particularly vulnerable to this. When the insulation chaffs and
cracks, the risk of electrical fires increases. Also, chaffed and cracked wire insulation
can cause control malfunctions. By far, the most dangerous wire failure is a phenomenon
called "arcing, in which and exposed wire comes in contact with [another] metal object,
[typically] the frame of [the] aircraft or another exposed wire, to create a short circuit" [4].
When this happens, it creates large amounts of heat, which can ignite the insulation. The
fire can then travel down the wire consuming more insulation and exposing more wire.
Obviously, any system in which this occurs will fail. Worse, the affect can potentially
spread to other systems causing them to fail as well [4]. "Other less significant electrical
system problems involve open circuits, bolted short circuits, intermittent open circuits,
and degraded shielding. Nevertheless, even these minor failures could prove to be
catastrophic, should they occur on critical systems" [4].
2.2 Current Methods Used to Detect Faulty Wiring
Unfortunately, there is currently no widely accepted, widely available method for
detecting faulty wiring. Some industry experts believe the triboelectric response may be
usable to determine the condition of a wire.
7
3.0 Theory
The theories utilized in this project are the theory of the triboelectric effect and
the theory behind signal response. Both are discussed in the following sections.
3.1 Triboelectric Effect
The triboelectric effect is more commonly known as static electricity. It occurs
when two materials slide against each other. In the case of electrical wiring, the two
materials are the insulating and conducting materials of a wire. As seen in the figure
below, a frictional force from the two materials sliding against each other causes
electrons from one material to separate and reattach themselves to the second material.
This creates a charge imbalance between the two surfaces, and the current induced from
this imbalance creates unwanted noise and interference. To a certain extent, this is
unavoidable in a signal.
Figure 2: Relative movement between insulating and conducting surfaces induces a
current [5]
8
The magnitude of the triboelectric effect is dependent upon numerous factors, such as:
• material composition
• the humidity to which the material is exposed
• the strength of the frictional forces
• the rate at which the electrons separate from one material and reattach themselves
to the other
A general equation for the current induced between two materials is [4]:
DMQC
DkMvi
n
+= (3.1)
Where
k = proportionality constant, which is unique to the material M = mass flow rate D = average particle diameter v = particle velocity n = exponent, which is unique to the material Q = charge on contacting particles i = triboelectric signal C = proportionality constant
The relationship given in this equation may be applicable to a straightforward situation,
such as a single particle running along a surface, but is difficult to apply to more
complicated problems, such as quantifying the aged state of a wire with electrical current.
Because these factors will change with the age of the wire, WECF did not find it
necessary to attempt to quantify each parameter. However, we still expect to find a
relationship between the state of the wire and its triboelectric response.
9
3.2 Frequency Response
Frequency response is a system’s response characteristics to a wide range of input
frequencies. Frequency response is usually discussed in terms of gain and phase. The
general transfer function of the system is expressed as [4]:
)()(
)( 0
fGfG
fHi
= (3.2)
Where
H(f) = system transfer function )(0 fG = frequency spectrum of the output signal )( fGi = frequency spectrum of the input signal
There are two methods for analyzing the frequency response of a system:
• A single frequency signal is applied to the system and the amplitude of the
resulting output is measured. To determine the gain of the system, which is the
ratio of output and input amplitudes, this process is repeated for a range of
frequencies [4].
• A random noise signal is applied to the system and its instantaneous response is
measured. This is performed in order to simultaneously test all frequencies in
question. For this method, the frequency response is the ratio of the cross
spectrum and the autospectrum of the input [4].
10
4.0 Laboratory Specimen
4.1 Wire Selection
To provide some constancy with the previous work done on this project, we have
decided to continue to work with ALPHA 1632 wire. This wire has rubber insulation and
was initially suggested to previous groups by Frank Wise, the department electrician, as a
type of wire that might deteriorate quickly. We have also decided to cut this wire into the
same size segments. We did purchase red wire to help immediately distinguish from the
black wire used last fall.
In addition, Dr. Stearman has suggested that we test a wire with Teflon insulation,
as Teflon is a more common insulator in industry. Teflon is tougher than rubber. It is
more resistant to corrosion and temperature extremes than rubber. Also, it has a much
lower coefficient of friction, and, therefore, presumably, has a less pronounced
triboelectric effect [8]. ALPHA 5852 was selected for its low price, Teflon coating, and
because its other characteristics seemed to be average. A smaller diameter, higher gauge,
was chosen for the Teflon wire, based on the fact that a narrower wire has a greater
surface area to volume ratio. WECF is confident that this will make it more susceptible
to corrosion than a similar, thicker wire. In addition, we predict that this high surface
area to volume ratio may cause it to have a more pronounced triboelectric effect than a
similar, thicker wire. We tried to find literature to either support or refute this theory, but
were unable to find any. Also, a narrow wire has the added benefit of being less
expensive. This allows us to make longer segments of wire, which we believe should be
beneficial. It stands to reason that shaking a long section of wire would generate more of
a current than shaking a small section of wire.
11
ALPHA 1632 ALPHA 5852
Figure 3: Alpha Wire Spools
Some additional specifications for the wires we are using are presented in Table 1.
Table 1: Wire Specifications [8]
Alpha Wire 1632 • Hook-Up wire, Test Lead wire • Copper wire with rubber insulation • 20 Gauge (thick) • Stranded, Tinned Copper • Rubber Insulation • -30o to 90o C
Alpha Wire 5852 • Hook-Up wire • 28 Gauge (thin) • Stranded, Silver-plated Copper • Teflon insulation • -60o to 105o C • Low Friction • High Chemical Resistances
12
5.0 Phase I: Laboratory Aging
5.1 Data Collection Cycle
In order to improve the size of our data sets, we deemed it necessary to restructure
the data collection procedures. The fall 2002 wiring group was limited to collecting one
point of data at any given time during the aging processes, because of their collection
methodology. They began aging all their wire segments at the same time. Then,
periodically, they would remove one sample at a time from each aging process, test it,
mark it, and not return it to the aging process afterwards [4]. In order to avoid such
limitations, we will, instead, remove every sample simultaneously at every collection
time. All the samples will be tested, and then returned to the aging process afterwards to
perpetuate the study. In this way, data yield at a given time will be increased ten fold as
there are ten wire samples for each aging process.
Figure 4: Data Collection Cycle Comparison
In addition to increasing the size, and thus the robustness, of the data sets, there
are other side affects of the new method. One positive side affect is that, because the
samples are always returned after testing, there does not need to be a set date for the end
13
of the aging process. Thus, the summer group will be able to continue further aging of
the same samples immediately should they choose to do so. A negative side effect will
be the loss of the ability to retest data at a later date. Because the samples are effectively
recycled, there will be no way to recheck the previous conditions of the samples once
they are returned to the aging process. Should a problem in the testing be discovered
later, it will be impossible to correct. Thus, great care must be taken to make sure that
the samples are evaluated correctly before aging is resumed. Also, due to the extra
burden of testing so many samples at once, we will probably be taking data every week
or every other week rather than every half week, as the fall 2002 group did. In addition,
Visual inspections will be impacted by the new procedures. The fall 2002 group would
strip the ends of the insulation off the wire samples when they were removed from aging
[4]. Stripping is necessary to allow the wire samples to be hooked up to electronics. It
also provided visual data of what had happened to the wire underneath the insulation. If
the samples are to be repeatedly used, they must be stripped from the beginning. The
exposed ends will have to be protected with removable covering of some sort, and will
not be a good representation of the rest of the wire. However, there is a simple solution
to this problem. A group of short wire segments, perhaps only two inches, cut from
surplus wire, can be added for the sole purpose of providing visual data. These mini-
samples will be removed one at a time, partially stripped, tagged, and preserved for side
by side comparison. After considering the possible ramifications, it was decided that the
benefits of the new data collection procedures outweighed trade offs.
5.2 Aging Processes
14
The aging processes we will be exploring this semester fall into two general
categories, temperature plus humidity, and corrosion. The fall 2002 group performed
temperature and humidity processes separately. They were unable to realize the desired
results from heat alone, but attributed this to an inability to achieve adequate heat due to
facility restrictions [4]. By acquiring our own equipment, we hope to reach higher
temperatures. We have also decided to examine the effects of cold temperatures. It may
be a coincidence, but both TWA 800 and Swiss Air 111, probably victims of wire failure,
flew in cold conditions [4]. Furthermore, we firmly believe in the potential of cycling
back and forth between temperature extremes. Although the fall 2002 group found only
minimal results from humidity alone, we believe the presence of moisture will be an
important component of the temperature plus humidity aging processes, especially when
cycling between hot and cold [4]. Adding water will generate periods of freezing and
thawing which will apply mechanical aging on a microscopic level. We are very
optimistic about this combination.
The corrosion aging processes will simply involve exposing the wire samples to
corrosive solutions by means of soaking. The two corrosives to be used are the same as
those used by the fall 2002 group, Jet-A fuel and Salt-water solution. Both corrosives
yielded some results. The saltwater solution had corroded the conductor, and fused the
strands together. Also, the wire exposed to saltwater became noticeably more brittle.
Figure 5: Aged Wire Samples [4]
15
The Jet-A fuel had a definite visible affect on the rubber alpha wire, particularly in
significant swelling of the insulation [4].
There is a disconcerting potential side affect from using corrosive soaks, and that
is how any residue that might be left behind might alter the triboelectric response. To
illustrate this concern, consider that, to reduce the triboelectric affect, some wires are sold
with graphite lubricant in between the insulator and the conductor. The graphite serves to
reduce friction and therefore reduce the triboelectric effect [9]. Thus, the presence of
another form of matter can alter the triboelectric effect without altering the age of
condition of the wire. Therefore, it may be possible that salt deposits, or residual Jet-A
fuel could upset the data. One solution would be to remove the foreign material before
testing. Salt could probably be partially removed by a brief, fresh water wash or soak.
Jet-A fuel residue might be more challenging to deal with. Fortunately, if residue does
have a significant effect, we believe it should affect the data consistently. Thus, if
residue is important, the initial application would result in a dramatic change, and then a
constant, unchanging affect.
In addition, we plan on having a group of wires that cycle through all the different
tests. We are also considering the possibility of having groups of wires that are under
tension while aging. In an email to the fall 2002 group, Ronald Galvez of the NASA
Integrated Wire group mentioned that wires under tension tend to age more quickly [10].
Though vibration was specifically mentioned as a potential cause of wire
deterioration, it is not being used in our age processes, because it was deemed to difficult
to accelerate the affects.
16
5.3 Aging Equipment
Certain Equipment is necessary to age the wires. The corrosive tests merely
require the corrosive agent, and a large enough bucket. Temperature and humidity,
however, require a more elaborate setup.
Several options were examined for a heating element. Commercial, kitchen ovens
were eliminated because one could not be found that was rated safe for continuous use.
Drying Ovens were quickly ruled out because they are designed to remove humidity.
After a good deal of searching, incubators were also ruled out initially, because one could
not be found with sufficient heating abilities. Thus, we began to consider environmental
chambers. The environmental chambers showed some promise. They were capable of
both hot and cold temperatures beyond our needs. Many could control humidity, and
several were programmable. Programmability would be particularly nice as it would
allow the temperature cycling to be automated and, thus, more frequent. Finding
adequate information on the specifications and prices of environmental chambers was
difficult, and could only be accomplished with calls to companies. Unfortunately, we
could not find a model within our reduced budget. Two units were found for about
$7,000, but these were refurbished, and only came with a three to four month warranty.
Even these were too expensive. The UT surplus on Pickle campus was contacted, but
they had had auctions a few weeks earlier, and did not have any useful equipment on
hand.
Fortunately, Dr. Stearman discovered that the Zoology department had and old
incubator and an old freezer that they no longer had a use for. He was able to secure this
equipment for us for free. Furthermore, it was his understanding that the incubator, a
Labline model, was capable of generating the levels of heat desired. Once the freezer,
17
formerly used to store dead animals, is cleaned by the university, and a Labline
technician can come out to inspect the incubator, we will be able to take possession of the
equipment.
Figure 6: Freezer Donated by UT-Austin Zoology Department
The freezer is not designed to control humidity, thus, something must be done to
retain moisture during the cold treatment. The most likely option is placing the wires in
small, sealed containers. Also, if wires are to be placed under tension during aging, some
type of apparatus, perhaps a rack, will be needed for that purpose. If we decide to
employ tension, we will seek the advice of Ronald Galvez.
5.4 Anticipated Results
It is expected that, as the wire deteriorates, its material properties will change. As
the insulation loses its elasticity and corrodes, its texture, friction characteristics,
18
impedance, and/or ability to retain or absorb charge my change. In addition, the
conductor may corrode or develop cracks, and it material properties could, therefore,
change as well.
Furthermore, it is expected that these changes will be reflected somehow in the
triboelectric response. The changes should exhibit definite trends that, hopefully, can be
eventually related to the condition of the wire.
19
6.0 Age Analysis
Once aged sections of wire have been acquired, either through laboratory aging or
from aviation scrap yards, their triboelectric response must be obtained. This is done by
exciting the wire with a known harmonic vibration and measuring its open-circuit
electrical output. This electrical output is the triboelectric response of the wire, and is
expected to vary with both the condition of the wire and the frequency of the excitation
vibration.
6.1 Experimental Setup
The experimental setup has four major components: signal analyzer/computer,
data acquisition system, signal amplifier, and electromagnetic shaker. The components
are connected in the manner utilized in a previous study by Steinbarger, et al [4].
6.1.1 Signal Analyzer/Computer
A Dell computer controls the entire experiment through the interface of IDEAS, a
laboratory measurement and analysis program. The IDEAS program is used to generate a
known harmonic signal that excited the wire. The electric response from the wire is then
acquired by the program, plotted, and analyzed. Two types of signals will be generated
by IDEAS, and the wire’s responses analyzed: a periodic function of known frequency
and amplitude, and a random noise vibration consisting of many periodic signals with a
range of frequencies. The former signal is useful to determine the effect of a wire’s
physical condition on its triboelectric response at a given frequency. That is, the manner
in which a wire’s triboelectric response varies as the wire deteriorates. The latter signal
20
is used to determine the frequency response of a wire. The purpose here is to determine
whether or not the frequency response of a wire varies with the wire’s physical condition.
6.1.2 Data Acquisition System
The Hewlett Packard 3566A/67A Data Acquisition System serves as the interface
between the computer and the wire/electromagnetic shaker setup. The device is
necessary to convert the digital signal that the computer generates to the analog signal
that is needed to operate the electromagnetic shaker. Additionally, the analog signal
generated by the triboelectric response of the wire must be converted into a digital format
before it can be sent to the computer.
Figure 7: Signal Analyzer, Amplifier, and shaker [4]
6.1.3 Amplifier
The analog signal output by the data acquisition system is not powerful enough to
operate the electromagnetic shaker. Thus, the signal has to travel through a MB
Electronics 125V Power Amplifier. Following the precedent set forth by Steinbarger, et
al, the amount of amplification is kept constant and all changes in the amplitude of the
excitation signal are made via the IDEAS interface [4].
21
6.1.4 Electromagnetic Shaker
The electromagnetic shaker is powered directly by the signal output from the
power amplifier. It vibrates in the axial direction according to the amplitude and
frequency specified in the IDEAS interface. A stinger is used to protect the shaker by
indirectly connecting it to the wire specimen under examination. Should the motion of
the system approach the safety limits of the shaker, the stinger will fail before the shaker
is harmed.
6.1.5 Electromagnetic Interference (EMI) Reduction
A previous study by Steinbarger, et al, has suggested that electromagnetic
interference (EMI) may have originated from and influenced the various components of
their test setup [4]. It is believed that this interference generated a large amount of noise
that was erroneously incorporated into the response signal from the wire. Such an effect
would help to explain why the group was not able to reproduce a response from a single
wire specimen with any acceptable degree of accuracy. Consequently, several methods
for reducing EMI in the laboratory area are utilized for this study.
First, the data acquisition system and the power amplifier were separated in
order to limit the effect an electromagnetic field generated by one unit might have on the
other. During the aforementioned study, these two units were located one on top of the
other. The data acquisition system, amplifier, and shaker will all be placed inside
grounded foil enclosures as a means of shielding them from EMI. This was suggested by
many sources, including the Alpha Company, which provided the wire that is being used
for this study [6]. Alpha also suggested shielding the wire itself with fully encompassing,
22
grounded foil. We are, therefore, considering placing the wire inside a section of PVC
pipe, which will be wrapped with grounded foil. The PVC also provides us with the
straight and rigid platform, desirable for shaking the wire. We are still researching
whether aluminum foil or copper foil would be the better option. An electromagnetic
field (EMF) meter will be purchased for the purpose of verifying the absence of EMI in
the vicinity of the testing equipment.
6.2 Anticipated Results
Exhaustive analysis of the mechanics behind the triboelectric effect in a wire have
led Woolrich Engineering to model the excited conductor/insulator interface in a wire as
an AC voltage source. The shaker transfers kinetic energy into the wire system, a portion
of which is transmitted to the conductor/insulator interface as friction. A rough
approximation of this friction energy can be derived from the analyzing the work done by
the insulation as it moves past the conductor a length dx , as illustrated in Fig. 3.
Figure 8: Wire/Electromagnetic Shaker System
dx
Shaker
Wire
V
L
R
23
The force normal to the surface of the conductor is equal to the hoop stress applied by the
insulation multiplied by the surface area of the conductor. The force of friction is then
given by multiplying the normal force by the coefficient of kinetic friction. Then the
energy imparted on the system by friction is given by the frictional force multiplied by
the relative axial displacement of the two objects, dx . This result is summarized by the
following equation:
6.1
This energy input causes electrons to be stripped from both the insulation and the
conductor. Much like a redox reaction, one of the materials loses electrons at a faster rate
than the other given the same rate of energy input [7]. This idea is illustrated by Fig. 4,
where the magnesium electrode is clearly more negative than the copper electrode.
Figure 9: Differences in Redox Reaction Rates Can Create an Electric Potential Between Two Materials [7]
( ) dxrLE khoop µπσ 2=
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Thus, there is a net movement of electrons from one material to the other. This will
either create a surplus or dearth of negative charge in a localized area of the conductor.
Since the charge has remained the same in the parts of the conductor that are not
experiencing vibration, an electric potential now exists along the conductor. This will in
turn induce a current. As the motion resulting from the shaker changes direction, the rate
of energy addition into the system decreases, and the potential between the insulation and
the conductor can no longer be maintained. The local equilibrium is reestablished,
creating an electric potential in the conductor that is opposite in polarity from the original
potential. This causes current to be induced in the opposite direction, thus creating
alternating current.
Based on the above discussion, and the friction energy equation derived earlier, it
is expected that the amplitude of the voltage induced as a result of the triboelectric effect
will vary with the coefficient of kinetic friction, and the rate at which each material loses
electrons, given a specified rate of energy addition ( insulationR and conductorR ). Thus,
6.2
Woolrich Engineering believes that the material constants in the above equation
will change in a predictable manner as a wire ages, and so the voltage should also vary
with the age of the wire. WECF hopes to find an empirical formula that describes this
variation in the voltage produced through the triboelectric effect as a function of a wires
age/physical condition.
( )
= conductorinsulation
k RRdt
dEVV ,,µ
25
WECF will also check to see whether or not the triboelectric effect-generated
frequency response of a wire varies with the age and physical condition of a wire. It is
not clear what to expect from this part of the study.
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7.0 Work to be Completed
In contrast to the first half of this study, which was focused on research and
design, the next month and a half will be oriented toward verifying the test setup and
generating results. There are also a few items that must be acquired.
7.1 Acquisitions
Woolrich Engineering Consulting Firm (WECF), with the assistance of Dr. R. O.
Stearman, has acquired a freezer and an incubator (capable of varying heat and humidity)
free of charge from the Zoology Department at the University of Texas at Austin.
However, these units are not yet ready to be used for the purpose of aging wire
specimens. The freezer was used to hold biological specimens, and so must be sterilized
and inspected by University authorities. The incubator must be inspected by a technician
from Labline (the incubator’s manufacturer) before it is put back into service.
Foil and cardboard boxes must be purchased for the construction of shielded
enclosures for the various laboratory devices used in the age analysis test setup. PVC
pipe will be needed for the enclosure for the wire. Additionally, an EMF meter must be
purchased in order to verify that EMI is not influencing the experimental results. WECF
was unable to find an EMF meter with the desired range in frequencies that could
interface with a computer, so real-time monitoring of EMI will be required during
triboelectric testing.
Finally, aged wire samples must be acquired from an aviation scrap yard in
Dallas. Dr. R. O. Stearman has arranged for WECF to obtain this wire free of charge,
along with the operational history of the specimens. The history of the wire will be used
27
in conjunction with lab tests performed at the University of Texas at Austin to look for
qualitative trends in the aged dependence of a wire’s triboelectric response. A member of
WECF will likely travel to Dallas to pick up the wire in mid-to-late March.
7.2 Preparation of Experimental Setup
This is probably the highest priority going into the second half of the study. The
wire to be used for controlled aging experiments by WECF has recently arrived on site,
and must be cut into sections and possibly twisted into pairs. The EMI shielding
enclosures must be constructed and properly grounded. Additionally, a testing stand
must be constructed to hold each wire specimen in a uniform fashion while the
electromagnetic shaker vibrates it.
7.3 Verification and Testing
Once everything is physically in place, a new wire specimen will be tested for its
triboelectric response to a harmonic input of known frequency and amplitude. After a
short time period, the wire specimen will be tested again to verify the previous results.
Assuming the results are identical, within a reasonable tolerance, the specimen will be
removed from the testing apparatus and the IDEAS program shutdown. Shortly
thereafter, the same specimen will be reinserted into the testing apparatus and the IDEAS
program restarted. The specimen will be tested with the same excitation signal as was
previously used, and the resulting response compared with the first two experiments.
Assuming the results agree with each other, a new specimen from the same wire spool as
the first, and possessing identical dimensions, will be subjected to the same test.
Assuming the response of this second wire specimen agrees with that of the first to a
reasonable degree of accuracy, the test setup will have been verified. At this point,
evaluation of actual aged wire specimens can begin.
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8.0 Task Distributions
At the start of our project, WECF elected Robert Beremand as our project
manager. His responsibility includes organizing the team and its work, making sure all
components of the project are being implemented. All three members of WECF
contribute equally to the project, though each specializes in one of two major segments –
wire aging and age analysis. These technical areas were divided so as to increase the
proficiency of the work performed by the team. Robert Beremand is responsible for
researching and designing the laboratory aging tests. The design of the test setup and
analysis of the process we will assume to acquire a signal response are the responsibility
of Chad Hanak and Melissa Straubel. All members of WECF contribute and participate
equally to the project, and all are present during each of these phases.
Project Manager: Robert Beremand
• Research of lab aging • Design of lab aging
processes
Senior Engineer: Melissa Straubel
• Design of test setup for age analysis
Senior Engineer: Chad Hanak
• Analysis of signal response method
Figure 10: Diagram labeling the distribution of tasks
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9.0 Cost Analysis
The laboratory experiments and tests to be conducted in the second half of the
semester will require a minimal budget. WECF was fortunate to obtain an incubator
from the Zoology Department at no cost. They have also donated a freezer which we will
use for cold tests. Obtaining these two pieces of equipment at no charge has greatly
reduced our cost. The Jet-A fuel and saltwater solutions to be used for lab aging have
been left over from previous teams. Also, the Aerospace Engineering Department at the
University of Texas at Austin already possesses the laboratory equipment necessary for
age analysis: a signal analyzer, a data acquisition system, a wave amplifier, and a shaker.
The only purchase WECF has made thus far is that of the wire itself. One 1000 ft
spool of Alpha Wire 5852 was purchased at $120.90. Also, five 100 ft spools of Alpha
Wire 1632 were purchased at $36.88 for each spool. Our cost purchases, therefore, total
$305.30.
WECF is still researching electromagnetic field detectors. We will need to
purchase one for the age analysis portion of our project, and we expect the cost of this to
be between $100 and $200. Finally, we will need to obtain, foil, card board and PVC
pipe to construct the shielding enclosures, but these are all relatively inexpensive items.
Therefore, the total cost to conduct this project is relatively inexpensive.
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10.0 Conclusion
Significant progress has been made in the area of test setup research and design,
as well as in the procurement of necessary materials. The only major item that has not
yet been acquired is the used airplane wire from the aviation scrap yard in Dallas. A
member of WECF, along with Dr. Stearman, will make the trip from Austin to Dallas to
pick up this wire sometime before the end of March. Now that the test setup has been
redesigned in order to provide more consistent testing results, it must be physically
assembled and its operation verified so that testing of the wire specimens can begin.
WECF is optimistic that the changes made to the test setup and wire aging procedures
will significantly augment the ability to generate a useful qualitative (and hopefully
quantitative) relationship between a wire’s age/physical condition and its triboelectric
response.
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11.0 Works Cited
[1] Furse, C. & Haupt, R. (2001). “Down to the Wire.” IEEE Spectrum Online. http://www.spectrum.ieee.org/WEBONLY/publicfeature/feb01/wire.html (25 January 2003).
[2] Stoller, G. “Wired For Trouble.” USA Today. 09 November 1998. pgs 1B-3B. [3] Barr, E. “TWA Flight 800: What Happened to the 747?” Free Republican.com. http://www.freerepublican.com/forum/a3873a5167f9b.htm (3 March 2003). [4] Steinbarger, S., Bryant, D., and Shinagawa, Y. “Identification of Aging Aircraft
Electrical Wiring.” ASE 463Q Final Report. 6 December 2002. pgs 33-38. [5] Stearman, R. (2003). “A Study on the Insitu Identification of the Aging of Aircraft
Electrical Wiring.” (Project Quad-Sheet) University of Texas at Austin. [6] “Technical Data: Shielding.” Alpha Wire Company.
http://www.alphawire.com/pages/342.cfm (6 March 2003). [7] Clark, J. (2002). “An Introduction to Redox Equilibria and Electrode Potentials.”
Chemguide. http://www.chemguide.co.uk/physical/redoxeqia/introduction.html#top (6 March 2003).
[8] "Hook-Up Wire" Alpha Wire Company. http://www.alphawire.com/pages/pdf/176.pdf (6 March 2003). http://www.alphawire.com/pages/pdf/173.pdf (6 March 2003). [9] "High Resistance Measurements" http://216.239.33.100/search?q=cache:KBNb-PoWQ8sC:www.keithley.com/kei_assets/downloads/6584.PDF+graphite+wire+triboelectric+friction&hl=en&start=8&ie=UTF-8 (cached in www.google.com, site presently down) [10] NASA email to wiring group of fall 2002. Located in WRW 202
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12.0 Appendix – Timeline
Date Jan. 13 - 31 Feb. 1 - 15 Feb. 16 - 30 Mar. 1 - 15 Mar. 16 - 31 April 1 - 15 April 16 - 30 May 1 - 14Objective Group Meetings Preliminary Presentation Research Write Introduction Introduction Due Continue Research Evaluate Progress Write Mid-semester Report Mid-Semester Presentation Edit Mid-Semester Report Mid-Semester Report Due Continue Research Lab and Age Analysis Setup Data Collection and Analysis Final Report & Presentation Preparation Final Presentation Write Final Report Final Report Due
Note: indicates important dates