junior series- final report and analysis of lms

8/3/2019 Junior Series- Final Report and Analysis of LMS

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Application

Liquid Crystal Displays (LCDs) are rapidly progressing to become the dominant technology for both HDTV

displays and personal computer displays, amounting to a market of $27.4 Billion[1]

. As display technology

has evolved over the years, from Cathode Ray Tube (CRT), to filter utilizing LCD displays, and eventually

LED utilizing LCDs, the general population has grown accustomed to certain colors looking Blue orRed or Green, that is, having a certain spectral wavelength and range, as well as intensity. This has

presented a problem for engineers who must utilize the newest technologies while keeping consistencies

between spectral emissions from previous generations of displays. In order to verify the Blue seen is

actually the correct wavelength and intensity; engineers have been forced to develop Light Measurement

Systems, to quickly and easily display usable color values, for the various types of LCD display methods.

LCDs can employ several different methods for producing the different colors seen out of a display,

including; Dichroic, Absorption, and Narrow-Band filtering, or Light Emitting Diode (LEDs) technology[1]

.

The Dichroic, Absorption, and Narrow-Band filters all utilize backlighting, with a filter, to narrow the

bandwidth of the backlight in some way to a visible color value, whereas Light Emitting Diodes produce

their own narrow spectrum of colored light in a limited range of the visible spectrum.

The Light Measuring System (LMS) we developed is intended to be used to characterize color values for

various LEDs used in LCDs. This system is able to measure a specific pixel illumination scheme that

meets or exceeds the Client and Users needs as expressed in the following sections. This report also

analyzes and outlines the results obtained from primary testing of our prototype LMS, as well as an in-

depth cost analysis and recommendations for future prototypes.

Users Need

Our client has expressed several needs including both technical specifications, as well as social, and

financial requirements. Table 1. (Page 2 Top) shows a detailed list of the technical specifications and their

corresponding normalized weighting factors established during our preliminary research and experiences

with the client.


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Table 1. QFD MatrixNote: * Represent attributes or objectives that did not qualify for a weighting factor

Attribute Measurable Objective Weighting Factor

Operation Time 1-5 hrs Continuous 1.12

Stability

Repeatability +0.04 -0.04,

Reproducibility +0.1 - 0.1, 95%

confidence interval 1.83

Sample Cycle 5 Second ea.


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Figure 1. System Block Diagram. DisplaysThe breakdown of individual components

And their relation to the whole system.

The Power Source must be able to produce a minimum of 2.0 V at 20 mA, to power the red LED, and

produce no more than 2.5 V at 20 mA, in order to not burn out the red led[2]

. The Power source mustproduce 3.2 V at 20 mA, to power the blue LED, and no more than 4.0 V to avoid burning out the blue

LED[2]

.

The LED Filter Holderand base must be no larger than 5x5x5 and have a 2 inch s pread from input

LED light to the fiber optic cable. Additionally the Holder itself must be able to hold a round LED D=

0.23 and length 0.35 inches with 2 holes drilled for the power supply leads of .03 spaced .98 apart

centered on the LED[2]

. The holder should be stable, and not tip over, while maintaining structural integrity

and stiffness for the best possible values obtained. Tolerances should be as close as possible preferably

80% of received light from

the LED but some variability is allowable.

The Spectrometer should measure accurately within 10nm as Thorlab Specifies the LEDs are only

tolerable of 10nm individually[3]

. The spectrometer also must have a resolution approaching 5nm where

more resolution is better for more accurate chromaticity values. The spectrometer should be able to send

a digital readout of the collected data Via USB Cable to a computer with Ocean Optic SpectraSuite

installed. Ocean Optics Spectrometer was determined to have a resolution of ~1nm which is ideal

for our system.

Power SourceLED Filter

HolderFiber Optic

Cable

SpectrometerComputer


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The Computer used should meet the following basicsystem requirements[4]:

Microsoft Windows Windows 2000, XP

Apple Macintosh OS X version 10.0 or later

Linux Red Hat 9 or later, Fedora (any version), Debian 3.1 (Sarge), and SUSE (9.0 or later)

30+ MB of free hard disk space.1 USB Ports

The first step in accurately measuring the LEDs is to power them. The power source selected should

provide ample power to the specifications set above. The next step involves the placement of the LEDs

for optimal measuring and viewing output as they would be in an LCD Display. The Holders purpose is to

provide a stable environment, where the light emitted from the LEDs can be accurately collected from the

fiber optic cable. The fiber optic cable is utilized so a diagnosis of each LED, can be done a distance

away from the power source and loaded LED in the holder. This is useful in busy factory settings, in

which analysis should be independent of the factory work environment, on the factory floor. Thespectrometer uses a grating to break the colored light into much smaller individual wavelengths and

converts them into a digital signal. The computer subsequently takes that digital signal and using the

SpectraSuite software converts it into a usable format for us to analyze (Intensity vs. Wavelength), which

can subsequently be converted into chromaticity values, or compared to the manufacturers specifications.

By using our QFD Matrix and System Block Diagram our conceptual designs for the Holder portion of

solution were created, to optimize for the entire system and our attributes in the QFD Matrix.

Conceptual Design Solutions

Two conceptual designs were created in order to select the design that met the most performance goals

for our LMS. Figure 2. below shows each concept with basic dimensions.


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Figure 2. Conceptual Designs 1 and 2. The top middle partrepresents the LED holder Lego Piece that can be adjusted

for each of the 3 LEDS in either design case. The Lego piecefits into the three holes in each design.

Both concepts work on similar principles; however, Concept 2 (Turn-Dial) had more moving parts (Gear

shown above) and flexibility in modulating the distance between the LED and the fiber optic cable, to

optimize light entering the cable. Each design utilizes a Lego Piece , containing three pegs than fit into

three holes drilled into the base, to adjust for each of the three LEDs (R,G,and B). The Lego Piece

serves as the primary LED holding device, which should press flush with the inner tube that connects to

the fiber optic cable. This should minimize light lost from the LEDs and interference from outside light.

The two concepts were then ranked against each other in a Decision Matrix (Table 2).


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Table 2. Decision Matrix. Concept #1 (Stationary) Concept #2 (Turn-Dial)

Concept #1 Concept #2

Attribute/Criteria Score Weight Value Score Weight Value

Operation Time 9.83 1.12 11.0096 9.5 1.12 10.64

Stability 8.83 1.83 16.1589 8.5 1.83 15.555

Sample Cycle 9.17 0.73 6.6941 8.3 0.73 6.059

Maintenance 8.83 1.28 11.3024 6.83 1.28 8.7424

Size 10 1.38 13.8 10 1.38 13.8

Cost 8.5 0.73 6.205 6.33 0.73 4.6209

Usability 9.7 0.73 7.081 8.83 0.73 6.4459

Scheduling 9.17 1.83 16.7811 7.67 1.83 14.0361

Safety 9.83 0.37 3.6371 9.33 0.37 3.4521

TOTAL 92.6692 83.3514

In order to determine the Score value for each design, each design was ranked on a 1 to 10 scale to

whether or not it would meet the quantitative and qualitative parameter set in the QFD on page 2. A

design that scored a 10 meant it fully met the parameter, 1 meaning it had 0% probability of meeting the

parameter, and 5 meaning it had a 50% probability of meeting the parameter.

Concept #1 (Stationary), won in every category but safety, where it tied Concept #2 (Turn-Dial). This was

not surprising as Concept #1 remained the simplest making it the least high maintenance, and best at

maintaining optimal calibration. The only advantage offered by concept two was, increased flexibility in

calibrating, at the cost of a much more complex design, more maintenance, and calibration needed

before use.

Our final design was based almost explicitly on Concept #1; however, as a team we decided to opt for an

adjustable inner tube, in order to give us some minor flexibility within our design, without becoming

ultimately too complex. This allowed us all of the advantages of Concept #2 without providing the

disadvantages of the many moving parts and high maintenance.

Design Specifications

The Light Sources used in our project will be LEDs. The relevant specifications for each LED are listed in

Table 3 page 7.


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Table 3. LEDBasic Part Specifications for Optical and Electrical Properties[2][5][6]

Blue LED Green LED RED LED

Forward Voltage @ 20 mA

(V)

3.2,

4.0max

3.3, 4.3

max

2.0,

2.5Max

Center Wavelength

46510

nm 5255nm 63910nm

FWHM 25nm 35nm 17nm

Optical Power @ 20 mA 20.0mW 7.0mW -

Half Viewing Angle 8 9 -

Through the use of these specifications we determined the optimal fixed viewing distance for the LEDs to

the fiber optic cable was 2 ,by testing each LED individually in order to find a range in which accurate

measurements could be taken.

The filter holder or LED holder in our case must be able to hold the three different types of LEDs, and

maintain a 2 gap from the LED to the Fiber Optic Cable. It must also be cast in a 5x5x5 aluminum

mold, for its base and a 4x4x4 mold for its ABS part. Additionally, it must be under $500 in final cost

after completion. Team Purples filter holder is shown in Figure 3.

Figure 3. ExampleLED Two- Piece Holder. Properlytoleranced and specified designs can be

found in Appendix A

In order to sort the wavelengths, the spectrometer must be able to break the LED s light into at minimum

wavelength groups of 10nm, and at maximum 1nm in order to accurately meet the functional

requirements stated above.

The spectrometer should also be able to detect and transmit digitally the subsequently divided

wavelengths to a computer, which can read them and convert them into a graph of Wavelength vs.

Intensity, for comparison with CIE Chromaticity Functions, in order to determine the accuracy of the color

LED

Adjustable

Holding

Piece

Filter

Holder

LED Power

Wires

(to power

source

AdjustableAlignmentScrews

Through-Put

Tube

Fiber Optic

Connector

(To

Spectrometer)


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when observed from the human eye[7]

. Additionally the peak wavelengths and FWHM values can be

compared to the LED manufacturers specifications above, to see if the LEDs fall inside the tolerances

stated by the manufacturer.

Metallurgical Analysis of CastingIntroduction

Our LMS base/holder was cast from A356 Aluminum alloy. A356 is Aluminum with 7% Si .3% Mg and is a

very common alloy for casting. This alloy provided an ideal alloy for casting as it has a low density

~2.7g/cm3

and a relatively low melting temperature of around 615 C while also remaining heat treatable

to improve its strength. Sand casting with binder (ZCast501) was chosen as the appropriate method for

fabrication of the holder/base as it allows for intricate designs and molds to be created while maintaining

relatively low cost. Additionally, casting was chosen as a convenience method as it was readily available

for use. The Mg provides the ability to age harden the alloy for increased strength and hardness, while Si

improves castability. After casting the holder was then heat treated to T6 condition to improve hardness

and strength. As cast and T6 condition hardness measurements were then compared along with

microstructures to determine the success of the heat treating.

Casting Process

Mold Preparation

The casting temperature chosen was 720 C (Based on previous experience this temperature works well

with our specific suppliers alloy in casting) and general casting temperatures range from 677-788 C for

A356. Our mold (1256.1 cm3) was first designed in Solidworks with a single pour spout, six riser vents (to

allow for shrinkage during cooling), and a single parting dividing the mold in two pieces through the z-

plane (Figure 4.). The mold was then transferred to a Rapid Prototyping Machine and created using

ZCast501 sand and binding material. The mold was then placed in a catch tray and packed with

sand/clay to hold the two pieces in place (Figure 4. page 9).

Pouring & Machining

Following mold preparation approximately ~220 cm3of liquid A356 720 C alloy were poured from the

ceramic pour cup into the pour spout of the mold and allowed to cool for twelve hours (Figure 4 page 9.).


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Figure 4. Pouring of Casting of A356 Base. Noticethe six riser vents accounting for shrinkage, and the sandholding the two piece mold tightly in place during pouring.

After the casting was finished cooling a screwdriver was used to separate the mold from the casting

(Figure 5.)

Figure 5. Separating mold from casting.A screwdriver was used to separate theMold from the casting. The subsequent

Mold pieces were then discarded.

After mold separation the gating from the pour cup and risers was left behind (Figure 6. Page 10). It was

then machined off using a band saw leaving the nearly geometrically finished base part ready for

machining the screw holes for adjusting screws and the ABS Adjustable LED holder. Final weight was

562g. The casting was then heat treated to T6 condition.

Molten

A356

Riser

Vents

Catch Pan

Sand holding

two-piece

mold

2-Piece Mold


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Figure 6. Casting after mold separation.The gating from the pour spout and

riser vents was subsequently machined off.

Heat Treatment

Following casting a heating treating to the T6 condition was performed in order to analyze the effects of

age hardening on hardness of A356. Following the ASTM handbook for A356 sand casting heat treatment

the cast part was solutionized at 540 C for 12 hours to allow for the Mg particles to dissolve into the

aluminum matrix. The casting was then taken out and quenched into a water bath for ~5 seconds to

supersaturate the aluminum matrix. The casting was then placed into a furnace for 3 hours at 155 C

following the sand casting procedure. Following the heat treatment the casting was quenched again into

a water bath for ~3 seconds to stop the precipitation growth of Mg precipitates.

Hardness Values

Post heat treating samples of the A356 gating (As Cast) and A356 gating (T6) were compared using a

Rockwell hardness tester. Testing on the gating was initially done using the HRE scale, however, the T6

condition gating samples proved too hard to use the HRE scale so the HRB scale was used to

subsequently test all of the T6 sampled.

Results for the As Cast yielded a x= 31.31 and StDev= 16.21 HRE scale

Results for the T6 yielded a x= 20.84 and StDev= 5.96 HRB scale

The As Cast samples may appear to be harder, however, the HRB scale (1.6mm diameter ball used for

indenting) is used for far harder material testing than HRE scale (3.2mm diameter ball used for indenting )

and in reality the T6 is much harder than the as cast sample.

Gating from

pour spout

Gating from

riser vents


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Microstructure, Phase Diagram, and Hardness Connection

In order to validate that our heat treatment was successful in addition to hardness values metallographic

samples were prepared and analyzed to find evidence of a successful heat treatment. Samples were

compared at the 200x and 500x magnifications (Figures 7, 8, 9, 10).

Figure 7. (Left) As Cast Microstructure at 200x Figure 8. (Right) T6 Condition Microstructure at 200xNote the grains of silicon appear far more spheroidized in the T6 condition. Evidence of a eutectic type

structure is noticeable in both microstructures. Many of the tiny precipitates, formed during unequilibriumcooling, have spheroidized into larger grains in the T6 treated sample. The 200x magnification gives a

good view of the proportion of Silicon to Pro-eutectic Aluminum in the A356 alloy.

250 Micron

Bar

Unknown

Silicon

compound Lamellar

Eutectic

Structure

Tiny

Precipitates

Unknown

Silicon

compound

Spheroidized

Silicon

Grains

(Al) Matrix Si Grains


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Figure 9. (Right) As Cast Microstructure at 500x Figure 10. (Left) T6 Condtion Microstructure 500xThe unidentified silicon compound is visible in both microstructures, evidence it was not dissolved duringthe heat treatment. The Silicon grains are more spheroidized in the T6 condtion microstructure than the

As Cast. Note the lamellar structure in the As Cast sample of Silicon and Aluminum. The tiny precipitatesvisible in both microstructures do not appreciably contribute to the strengthening of either sample.

Lamellar Structure

The 200x magnification As Cast sample shows a nearly 50% eutectic structure, of Al and Si rich phases,

in a lamellar configuration. This corresponds with the phase diagram mass fractions for what equilibrium

an equilibrium cooled sample should have (Figure11.). The minor differences occur from some of the Si

that should be in the lamellar structure forms tiny precipitates due to non equilibrium cooling.

Tiny Particles

The tiny visible precipitate particles are formed due to the unequilibrium cooling rate after casting and thedecreasing solubility of Si in (Al) (Figure 11.). As the sample cools at non-equilibrium conditions most of

the Si in the sample has enough time to form the lamellar-like structure present in Figure 7, however,

some of the Si that is dissolved in the Al phase at 555C is no longer soluble as it cools and must

precipitate out into the tiny particles visible in the (Al) matrix phase and does not have ample time to

diffuse into large grains. Those precipitates are then once again almost completely dissolved during

solutionizing of the sample during heat treating as the solubility is once again raised at the higher

Unknown

Silicon

compoundUnknown

Silicon

compound

100 Micron

Bar

Lamellar

Eutectic

Structure

TinyPrecipitates

Tiny

Precipitates

Spheroidized

Silicon

Grains

Si Grains(Al) Matrix


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temperature. Solubility is then lowered again during quenching and more, tiny precipitates reform. During

the furnace treatment at 155C many of the smaller precipitates have enough energy to move either into

the spheroidizing lamellar grains or back into the (Al) rich matrix phase as solubility is once again

increased. When the final quench occurs fewer tiny particles are present as the solubility drop is less than

from solutionizing or As Cast cooling and particles have had more time to diffuse into the larger

spheroidized grains.

Figure 11. A356 position on Al-Si Phase diagram[9]

At nearly 50% of the distance between the eutecticComposition and maximum solubility of silicon in (Al)

A356 (7%) should have a nearly 50% eutectic lamellarmicrostructure as shown in Figure 7 with the rest being matrix

phase of Pro-eutectic Al.

Unidentified Silicon Compound

In all four samples an unidentified compound was found represented by the light grey grains in the (Al)matrix. Currently more research needs to be done in order to identify this unknown compound.

Hardness and Microstructure

The hardness of the sample is due to the formation of Mg 2Si precipitates during the T6 heat treatment.

These particles are much too small to be seen under the 200x or 500x magnifications available to use.

These particles form during the final step of the T6 treatment (Furnace t reat 155C as the heat from the

furnace allows the supersaturated atoms of Mg (formed during solutionizing) to move to lower energy

states, by spheroidizing tiny precipitates, that inhibit slip along slip planes. In order to actually observethese particles we would need to utilize a Transmission Electron Microscope. The tiny precipitates that

are visible are much too large to contribute to the strengthening or hardness of our alloy. As precipitates

grow to the micron or tens of micron scale they can no longer effectively interact with inhibiting the slip

along slip planes.


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Hardness vs. Strength

During our heat treatment we increased both strength and hardness. This is because both strength and

hardness rely on an increase in inhibition of movement along slip planes (proportional). Hardness is a

convenience measurement of resistance to plastic deformation while strength is a, much more difficult to

obtain measurement, is a reflection of resistance to slip along slip planes. Since strength measurements

were not used, CES gives maximum tensile strength of 174 MPa for As Cast A356 and yield strength of

114 MPa, while tensile strength increases to for 310 MPa for T6 and yield strength to 234 MPa[8]

. This

increase corresponds with our hardness increase found in our samples.

Conclusion

Although the precipitates were not visible under the microscope we know that the heat treatment was

successful based on the HRB scale being necessary for the T6 treated sample (as well as correctly

following the ASTM standards for sand casting A356). The spheroidization of Si being present in both the200x (Figure 8.) and 500x samples (Figure 10.) shows signs of some sort of heat treating and lowering of

energy within the grains of Si.

Fabrication and Assembly

Team Purples LMS utilized fiber optics to transmit light from the LED holder to the Ocean Optics

Spectrometer. The fiber optic cable utilized a 200 micron OD fused silica fiber that was fed into a

polyethylene tube, which was surrounded by Kevlar reinforcing fibers, and utilized an orange furcating

tube. An example fiber optic cable can be seen in Figure 12.

Figure 12. Fiber optic cable cutaway.[8]

the Kevlar reinforcing braided sheathas well as polyethylene inner tube

are both clearly visible.

Following the insertion of the core of the fiber, the ends of the fiber were then affixed using epoxy to an

SMA connector and a boot was placed over the connection to further protect the fragile fused silica fiber

(Step 4 of Calibration in the Standard Operating Procedures shows the boot and SMA connection). The


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cables chosen were one meter in length to show a proof of concept for the utilization of fiber optics to

allow analysis of samples to be done some distance away from the loading device.

The sample holder required minimal machining and manufacturing as most assembling is done at the end

client user level. A drill press was used to drill the three .250 inch diameter extruded holes for the LED

Adjustable Holding Piece in the cast base. Additionally a drill press was used to drill the four holes for the

four 6-32 hex head .138 adjustable screws in the base Step 1 of Set up Procedure in the Standard

Operating Procedures). A tap and die set was used to tap the holes for the screws to be loosened and

tightened from. All additional assembly and manufacturing is done by the final operator.

During assembly of the fiber optics problems arose with keeping the fused silica inner cable from sliding

out of the tube during the connection of the SMA Connector to the cable. This problem was magnified as

a result of the epoxy setting much more quickly than manufacturer claims. In the future it is recommended

to change epoxy manufacturers as setting the fiber on time proves difficult in the current time constraints.Additionally drilling of the three extruded holes in the base of the LMS provided difficult to align properly

by hand. In the future the holes should be cast into the base and then machined to spec to provide better

alignment and a more accurate position for the ABS LED adjustable holder to fit into.

Attenuation Causes by Constituent

In order to better pinpoint the location of the most attenuation in our system the System Block Diagram

was used (Figure 13.).

Figure 13. System Block Diagram. Displaysthe breakdown of individual constituentsand their relation to the whole system.

After creating the System Block Diagram, we ran through each constituent and tried to evaluate whether

the constituent contributed a significant amount to the total loss of attenuation, and if the constituent did

pose a significant loss, what individual component (I.E. fiber optic cable has multiple components, SMA

connector fiber, etc..) within the constituent lead to that significant loss.

Power SourceLED Filter

HolderFiber Optic

Cable

SpectrometerComputer


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Power Source The power source did not contribute a significant amount of attenuation as the light has

yet to have been produced at this point in the system.

LED Filter Holder The filter holder creates the most attenuation as there is light lost at multiple points in

the system (Leaving LEDs, passing through filter tubing, and passing into the fiber optic cable), however,

for our Light Measurement System calculating the loss is extremely difficult, as getting proper alignment

of the LEDs and the fiber optic cable, proves extremely difficult. Additionally the LEDs produce a radial

intensity distribution that is different for each LED, (color/wavelength) as well as each individually

manufactured LEDs. For the red LED, with maximum intensity at 8 off the normal in a conical shape, our

tube of 60.96mm decreases the intensity by a factor of 11.74 xs solely by placing the fiber optic cable

father away from the light source.

Fiber Optic Cable The fiber optic connection created minor attenuation. The SMA connections were not

perfectly aligned and the air to glass transitions also creates some minor refraction when entering the

spectrometer. Additionally the light also changed mediums three times before reaching the spectrometer.Each transition created minor refraction lowering signal quality. All of these factors helped contribute to

the light loss of the system.

Spectrometer The spectrometer itself did not directly affect the light entering it. Only the connections

between the fiber optic cable and spectrometer contributed significantly to attenuation.

Computer The computer did not contribute significantly to the attenuation of the light as it was only

processing the digital signal, and not helping the light flow in any way.

Total Attenuation & Recommendations

The total attenuation amounted to far less than 1% of radiated power actually entering the spectrometer

(Table 4.).

Table 4. Total Light Attenuation. Displays the system settings (left), Power in (mid),power measured out of fiber (mid), Resulting Attenuation (mid right), and corresponding spectrometer

settings for good readings (right).

Light Throughput Measurements

Voltage

(V)

Current

(A)

Power in

(watts)

Power transmitted through Fiber

Optic (watts)

Attenuation

total(dB)

Counts Integration

Time (ms)

Blue 3 0.01 20*10^-3 123*10^-9 52.11 60000 10

Green 4.1 0.06 7.0*10^-3 168*10^-9 46.19 60000 10

Red 1.8 0.01 7.2*10^-3 53.4*10^-9 47.67 48000 10


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Following the calculation of total attenuation, we then calculated the amount of photons of each LED

produced that were actually incident upon the photocathode. (Table 5.).

Table 5. Photons incident on the photocathode by wavelength.Magnitudes of x10^11 amount of photons are incident on the photocathode

each second.

Wavelength(m) Energy

(joules/photon)

Power received from spectrometer

(Watts)

Photons/Second

465*10^-9 4.27484E-19 123*10^-9 2.8773E+11

528*10^-9 3.76477E-19 168*10^-9 4.46242E+11

639*10^9 3.1108E-19 53.4*10^-9 1.7166E+11

After calculating the total attenuation we then calculated the attenuation lost by the fiber optic cables

specifically, so we could establish a general idea of what proportion of attenuation was lost prior to

entering the cables and then through the Fiber Optic Cable stage in our system Table 6..

Table 6. dB lost due to fiber optic connections.angular attenuation produces about twice as many dB

as Lateral

dB

Laterally

dB

Angular

0.3852dB 0.628

Although our dB values were high, indicating that minimal light from the LEDs was incident on the

photocathode through our LMS, upon initial trial testing all three LEDs (Red, Blue, Green) were able to be

tested at their corresponding integration times (Table 1.)

Although the data in Table 1. does not suggest a correlation between wavelength and attenuation (Due to

the lack of precision between measurements), as wavelength decreases diffraction increases, meaning

the alignment for blue light would be more difficult to obtain than red light, creating more attenuation do to

the extra misalignment of the fibers.


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In order to reduce our overall attenuation in the future, adding a lens to further column ate the light

entering the fiber optic cable may be used. By reducing the dB of the holder we will significantly reduce

the overall dB (Figure 14.)

Figure 14. Attenuation caused by holder vs. fiber optic cable.Attenuation caused by the holder makes up a large majority

of overall attenuation.

Testing Methodology

Standard Operating Procedure for LMS

Set Up Procedure

1. Take the aluminum baseplate and loosen the screws

to allow for future

adjustment

2. Obtain the adjustable lensholder and separate the

adjustable O ring so that the

piece resembles the picture

on the right

Attenuation Fiber optic

vs.

Holder

dB Lateral

dB Angular

Blue Led Holder dB


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3. Obtain the adjustable O ring

4. Attach the adjustable O ringto the adjustable lens

holder to the extruded area

as shown to the left. Twist

the O ring until it is flush

with the aluminum casting

5. Take out the 0.5 inchdiameter lens holder

6. Place the 0.5 inch diameterlens holder into the

extruded holder with the

screws as shown to the

right

7. Screw together the 0.5 inchdiameter lens holder and

the adjustable lens holder

so that it resembles the

picture to the right

8. Obtain another 0.5 inchdiameter lens holder, and

screw on to the end of the

lens holder, as shown on

the right.

Note: As of now, the model should

resemble the picture on the right

9. Take the pre-assembled

LED holder

10.Place the LED holder intothe extruded holes


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11.Adjust the adjustable lensholder until the front of the

0.5 inch diameter lens

holder is flush against the

LED holder

Calibration

1. Locate the end of the lensholder adapter

2. Look into the hole of thelens holder adapter to see if

the LED appears to be

straight

Note: If it is not straight, tighten

or loosen the screws on the casting

until the LED appears to be in a

straight line

3. Take the fiber optic cableand screw it to the end of

the lens holder adapter

until taught.

4. Screw the other end of thefiber optic cable into an

Ocean Optic USB4000

spectrometer

5. Spread the spectrometerand casting apart until the

fiber optic cable is straight

and taught

6. Plug in the USB adapterinto the Ocean Optics

USB4000 port


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7. Plug the other end of theUSB cable into a USB port

on a computer

Data Processing

1. Once the computer hasbeen turned on, open up

the Spectra Suite

application, which is

located in the Ocean

Optics folder from the

start menu.

2. Obtain a power source

3. Connect the LEDs to thepower source, the red

pin goes into the red

colored slot, and the

black pin goes into theblack slot.

4. Adjust the integrationtime to 10 milliseconds

5. Turn on the powersource, and adjust the

voltage and current for

each LED until a peak of

approximately 50000 to

60000 counts is

obtained.Approximate Values

Red- 1.9 Volts

0.1 Amps

Blue- 3.0 Volts

0.1 Amps

Green- 4.1 Volts


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0.6Amps

6. Copy the data obtainedby clicking on the copy

to clipboard button

7. Go to Microsoft Exceland copy the data into

column A, row 2.

8. Excel will calculate theexperimental

chromaticity values for x,

y and z and display them

9. Compare theexperimental

chromaticity values

against the acceptedvalues

Red: x=0.640, y=0.330

Green: x=0.300, y=0.600

Blue: x=0.150, y=0.060

10.Repeat steps 3 through 9three times for each LED

to obtain a statistically

significant amount of

data.

To enhance the performance of our LMS tighter tolerances between the LED Holder and the extruded

holes within the base would make alignment of the optical tube and LED much easier. Additionally

employment of specifically set power sources would eliminate the necessity for adjusting the power

source when powering LEDs and increase the ease of calibration and operation. Also possible

introduction of collimating lenses to better focus the light leaving the LED into the fiber optic cable may

improve light throughput and decrease attenuation when low intensity LEDs (ex. Red color) are used.

Results & Color AnalysisPost construction of our LMS samples were conducted on Thorlabs Red, Green, and Blue LEDs following

the SOPs outlined above. Five sample measurements were used to determine the amount of

measurements to be taken each day, however, the standard deviations of these measurements was so

small it revealed that a single measurement daily would yield significantly different results over the course

of the data collection. To yield more accurate data team Purple decided to take three measurements daily


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to yield a larger data pool to analyze. Measurements were taken within a one hour timeslot each day, by

separate operators daily, and consisted of three individual readings on each of the three different LEDs,

for a total of nine measurements daily. These measurements continued for five days providing 15

measurements for each LED. These values taken as wavelength vs. intensity were converted to

chromaticity values per client request through utilization of a Microsoft Excel Spreadsheet and

compared to those produced by CRT phosphors utilized in CRT displays (Table 7. page 23)

Table 7. CRT Chromaticity vs. LED Chromaticity. LEDs match upwell in the color red but deteriorate as the spectral wavelengths

get shorter.

CRT LED

Purple

Accuracy

Red Avg Offset 0.340

x 0.640 0.590 92.19 %

y 0.330 0.312 94.54 %

Green Avg Offset 0.074

x 0.300 0.205 68.33 %

y 0.600 0.653 91.17%

Blue Avg Offset 0.083

x 0.150 0.132 88.0 %

y 0.060 0.207 32.37 %

Based on the data collected above the LEDs tested from Thorlabs do not provide enough of a match,

based on chromaticity values taken, to completely replace the CRT Phosphors and maintain less than a

5% difference between chromaticity values. However, the human eye may not need a match to be within

5% and it may be possible to utilize LEDs without having a 95% match. We recommend additional studies

on the human eyes perception of the difference before drawing a final conclusion.

The results were also compared to group Brown to see if there were any variances between LEDsbetween different testing groups (Table 8. Page 24). A 2-Sample T-Test was used to determine if the

LEDs mean of the LEDs measured between the two groups were statistically similar or different.


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Table 8. Chromaticity Values (Team Purple vs. Team Brown). Only Red yand Blue x were determined to be significantly similar.

LED

Purple

LED

Purple

LED

Brown

LED

Brown

Statistically

Similar

Red Mean Std.Dev. Mean Std.Dev. P>alpha

x 0.5904 0.00963 0.60717 0.00275 No

y 0.3147 0.00279 0.31483 0.00066 Yes

Green

x 0.2182 0.00310 0.20956 0.01154 No

y 0.6558 0.00465 0.66902 0.00273 No

Blue

x 0.1342 0.01775 0.13707 0.00155 Yes

y 0.2226 0.00737 0.19402 0.00290 No

Only Blue x and Red y values were determined to be significantly similar. This is because the standard

deviations of both data sets were extremely small due to the precision of the two LMSs that were being

used to test.

Long term reproducibility for the 5 days tested was = 0.00193 < 0.1 Target for 2.

Short term repeatability was = 0.0075 < .04 Target for 2

The LMS fell within the target for both repeatability and reproducibility. The measurements would have

had an even lower standard deviation if we had used the same operator for all of the trials and not pulled

out the LED Adjustable Holder between each measurement. Additionally it is important to calibrate the

LMS the same way each day which was very operator dependent.

Conclusions

Our LMS met all of the clients original performance objectives and user needs. The LMS cost only ~$355

far less than the original budget of $500 dollars and provides stable repeatable measurements of LEDs.

The LMS is easy to operate and is safe to handle. No injuries were achieved during the 5 day trial with

multiple different operators. The LMS was completed within the 10 week timeline and can be operated

from 1-5 hours continuously. Samples can be loaded and tested within one minute. All previous

guidelines have been met.


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Project Plan

Table 4 (Attached Back) outlines a breakdown of both the timeline and work breakdown for completion of

our LMS. Initial goals that were provided during the conceptual design review can be found below.

During our timeline it is important for us to complete casting and fabrication of the LED holder and baseon time, as to allow sufficient time to test and calibrate our LMS for use. These two steps are the most

vital in completion time and represent the most crucial and strict deadlines to follow. After completion, it is

important for us to quickly fabricate and begin testing, so we may account for any potential problems or

delay towards completion of the overall project. Initial project estimates of total hours were ~380

hours.

Final hours actually amounted to only ~316 hours. Meetings originally intended for initial design and

fabrication time outside of class were eliminated as it was found they were not needed. The total cost

breakdown by task is shown in Figure 15.

Figure 15. Breakdown of Project Hours by task. All tasksrepresent major steps in the Gantt Chart. Over

half of the time spent on the project was on design

Overall hours could be reduced by eliminating drilling of holes in the base by casting them into the base.

Additionally automating the casting of the base and the creation of fiber optics could reduce total time.

Identify

Functional

Reqs.

16%Brainstorm

Solutions

9%

CDR

16%

Detailed

Design

13%

CAD Al Base

3%

CAD ABS Part

2%

BOM

3%

Fabricate

1%

Purchase Part

1%

Ca

st

Al

Ba

se

Drill Holes in Base

6%

RPT ABS

0%

Fab Fiber optics2%

Testing

4%

Analysis

6%

Communicate

11%

Final Design

Review

6%

Hours


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Identifying the functional requirements was the most important and thus should have the most hours in it

in order to ensure the client specifications are all met.

Cost Analysis

Throughout completion of the LMS a record of prototype material costs was kept through the use of a Billof Materials (Table 9.)

Table 9. Bill of Materials. Costs were calculateas quantity multiplied by cost per unit. Powder

binder represented the largest expenditurefollowed by the through-put tube hardware(Adjustable Lens Holder/Optical Tubes).

Bill of Materials Quantity Cost ($) Cost Total

($)

ABS Rapid Prototyping 1.68 10 16.8

Al A356 Casting Alloy 0.5559 4.1 2.27919

Powder binder 1256.06 0.15 188.409

Fiber Optic Cable 1 7 7

SMA Connector 4 9.95 39.8

Protective Coating 1 1.5 1.5

Epoxy 2 3.75 7.5

Epoxy Syringe 1 1.25 1.25

Polishing Pad 1 1 1

Screws 4 0.5 2

Adjustable Lens-holder 1 28.6 28.6

Optical Tube 2 15.3 30.6SMA to SMO Adapter 1 24 24

Retaining Ring 1 5.1 5.1

Total 355.83819

Total cost amounted to only ~$355 dollars much less than the target of $500 as discussed in the

functional requirements. More than half of the total cost (53%) was attributed to the powder binder for the

casting of the base for the LMS. In order to reduce costs in the future an alternative casting process or

binder should be used in addition to more optimization of CAD molding to reduce total binder used.

Additionally two fiber optic cables were fabricated while only one was needed for our design to work

which would have reduced total budget had only a single cable been utilized. Optical tubes and an

adjustable lens-holder were used to reduce interference from outside light. These pieces could have

easily been replaced with an ABS or similar polymer tube for the same function which could reduce total

overall cost.


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As stated in the Project Plan section total project hours amounted to 316 hrs. This time multiplied by

average engineering salary of 100$/hr gives a total project development cost of $31,600+355.83819

prototype cost. Recommendations for reducing these expenses are outlined in the Project Plan and

Cost Analysis sections.


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Appendix A


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Appendix A (Cont.)


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References

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