Paper - the Department of Mechanical Engineering and Applied
Contents
1. for each test The pneumatic actuator concept which is a modification of the applied weights concept was ultimately chosen as a more elegant and neater solution with the ability to provide variable pressures for different TE devices and greater usability for the end user 4 DESIGN DESCRIPTION 4 1 __ Overall System Design In TECLA the TE device whose performance is being characterized is sandwiched between a heat source and a heat sink which have smooth and flat surfaces Sufficient and consistent contact pressure is applied to the TE device during the test Temperature and voltage are measured and processed on a PC Figure 3 shows the overall construction of TECLA MEAM 446 2012 11 Figure 3 Exploded View of the Main Parts of the TECLA Assembly Thermoelectric Device The remainder of this section is used to provide the analyses involved in the design decisions for different components of TECLA 4 2 Contact Pressure During preliminary testing of TE devices we learned that there is a strong correlation between output voltage and force exerted on the TE device The plot in Figure 4 provides testing data showing the effect of an applied pressure on the output voltage of a given TE device at a constant temperature difference Figure 4 shows the results of the test that was done to show the dependence of voltage on applied pressure This test was performed by heating the TE device to a steady state condition vary2. apply pressure The appropriate amount of weight would be determined by the size of the TE device and the desired pressure 3 1 3 Pneumatic Actuator This design is identical to the previous candidate design concept applied weights except for the mechanism ensuring uniform contact and sufficient heat transfer In this design a pneumatic actuator controlled by compressed air would be used to apply pressure to the TE device surfaces 3 2 _ Comparison and Downselection The liquid baths concept has two main advantages first perfect contact between heat source sink and TE surfaces second ability to control temperatures precisely and accurately However it was the least feasible design due to limitations in liquid temperatures extensive insulation of electronics from liquids sealing of liquid containers and perhaps most importantly ease of use This concept would likely be a apparatus for research use i e The user would not be able to switch in and out the TE device between tests easily The applied weights concept has the advantage of being much neater in its construction compared to the liquid baths concept It is also able to control and measure hot and cold side temperatures with proper placement of measurement devices However it has a critical disadvantage of not being able to continuously vary the pressure on TE devices and requires the user to manually place weights that would be quite cumbersome to handle for most users
3. efforts have created a need for a reliable and consistent lab apparatus to characterize TE devices Prior studies have explored novel testing methods for characterization of TE devices 3 identifying the variables that must be controlled to accurately characterize them i e MEAM 446 2012 11 contact pressure presence of thermal grease etc However to our knowledge there has been little effort to aggregate the different factors identified by past studies and consolidate the measurement techniques into a single laboratory apparatus This project aims to create a reliable apparatus by which TE devices can be characterized 2 REQUIREMENTS AND OBJECTIVES This project aimed for TECLA to achieve the following objectives e Simultaneous variation of hot and cold side temperatures e Continuous measurement of hot and cold side temperatures and voltage output from TE device e Uniform surface contact across TE device to ensure consistent heat transfer e ase of use for the operator e Development of PC interface to collect and process data e Ability to accommodate TE devices of various dimensions height width and thickness e Minimal manual adjustment from user during testing e Compact size 3 CANDIDATE CONCEPTS 3 1 Description of Design Concepts The two basic principles needed to test a TE device are temperature difference and uniform contact between the TE device surfaces and the heat source and heat sink These prin
4. heat is generated to reach temperatures as high as 250 degrees Celsius In order to make this hot environment safe for the user a transparent enclosing box was made The user would be able to observe the test without being directly exposed to this heat 5 PROTOTYPE REALIZATION 5 1___ Overall Prototype Description A commercially available scientific hot plate Cimarec was used to raise the temperature of the hot side of the TE device The hot plate is capable of achieving temperatures up to 450 degrees Celsius which is beyond 250 degrees Celsius the upper limit for most TE devices MEAM 446 2012 11 A copper CPU cooler with a gold plated conductive surface CPU 300 V10 Koolance was retrofitted to cool the cold side of the TE device An integrated liquid cooling system EXT 440CU Koolance was used with the copper cooler The cooling system is able to cool the TE device down to approximately 30 degrees Celsius over time a wide range of temperature difference can thus be created enabling complete characterization of the performance of the TE device The heat sink was retrofitted with custom machined parts for seamless integration into the TECLA The liquid cooling system circulates the coolant into the heat sink providing additional cooling capability The liquid cooling system shown in Figure 7 is a combination of a heat exchanger a pump and a reservoir The fan power and the coolant pump speed can be controlled to vary the
5. yet run successfully on 64 bit We advise running the current GUI on 32 bit In order to make this procedure easier on the user a video demonstration of how to use TECLA will be provided to the user MEAM 446 2012 11 page 12 Copyright 2012 by the authors
6. MEAM Senior Design Paper MEAM 446 201 2 11 Senior Design Project Final Report April 27 2012 Department of Mechanical Engineering and Applied Mechanics School of Engineering and Applied Science University of Pennsylvania Philadelphia Pennsylvania USA TECLA THERMOELECTRIC CHARACTERIZATION LAB APPARATUS Ellen Chang Anam Omar Jennifer Lukes Php Noah Granieri David Kim Shengxi Yuan Robert L Jeffcoat PhD faculty advisor instructor Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania ABSTRACT TECLA thermoelectric characterization lab apparatus was developed in order to characterize the performance of thermoelectric TE devices TE devices utilize temperature differentials to produce voltage TECLA 1s able to vary the hot and cold side temperatures of TE devices using a scientific hot plate and a liquid cooling system accurately measure hot and cold side temperatures using thermocouples accurately measure the voltage output using a precision voltage sensor apply uniform contact pressure across the surfaces of the TE device using a pneumatic actuator allow easy access to the TE device between tests and interface with the user via a MATLAB program to collect and process test data TECLA produces repeatable results consistent with known TE data Therefore TECLA is a reliable test apparatus for research in the field of thermoelectric power generation technolo
7. S O10 O O W OD 23 8 12 5 60 45 17 8 11 0 23 8 12 5 m e V ep o D Ui 0 8 1 1 V O N Ww 3 6 10 8 lt ji OIA U N 0 6 W U N CO W 1 cMaster cMaster cMaster cMaster Wm ion 35 7 18 2 12 2 14 9 35 2 1 3 35 7 9 1 6 1 7 4 17 6 YY OD gt Ww U gt a lt SS Surface Hinge cMaster Linear Bearing McMaster xternal Retaining Ring for Linear Bearing for 5 8 OD McMaster teel Draw Latch Pack of 5 McMaster ood block Red Oak School of Design w wW D N ADV S m O W D m a U 0 0 0 0 0 0 Eg EE E Ee v u E 00 00 Ti U gt l D Total qty Cost item_ Total Cost 2000 20 0 1500 0 06 90 0 0 21 9 6 1 Laptop Computer Noah Grane 1000 00 Total 1 252 29 N WIJO O vu g D 1000 0 1 137 90 O MEAM 446 2012 11 page ll Copyright 2012 by the authors APPENDIX B TECLA USER MANUAL 1 Make sure all components requiring power are plugged in hot plate cooling unit 2 Open box and place thermoelectric device on hot plate Make sure hot side of TE device is face down i e on conventional TE devices when hot side is faced down red lead is on right black lead is on left 3 Close heat sink unit on top of TE device 4 Plug leads of TE device into lead labeled Thermoelectric coming out of circuit box 5 Plug batteries po
8. ST SUMMARY The materials cost of the prototype TECLA was approximately 2 380 of which 1 338 was associated with items made available on loan or from MEAM supplies 1 252 of the 1500 MEAM authorized budget was spent leaving a surplus of 248 EMBEDDED EXPENDED and CONSUMED ITEMS Description Source Cost item Total Cost ooling System heat sink tubing pump heat exchanger coolant ower adapter Koolance cientific Hot Plate McQueen com BrandNewEngines Phidgets Inc Phidgets Inc Phidgets Inc Coolerguys com O 354 60 189 00 141 16 354 60 189 0 141 1 46 6 97 0 75 7 20 5 ao V JO Ov O ir Compressor O hermocouples emperature Phidget oltage Phidget and interface kit rtic Silver 5 Thermal Paste 12g wiftech HydrX Coolant Coolerguys com crylic Cement and Syringe Applicator Tap Plastics Steel Shaft 1 4 OD 7 Length McMaster Steel Shaft 1 8 OD 4 Length McMaster Anodized Aluminum Shaft 38 Diameter 18 Length McMaster SS Flat Head Machine Screw 8 32 Thread 1 25 Length McMaster Pneumatic Actuator McMaster Blue Polyurethane Tubing 1 4 OD 0 16 1D_ McMaster Clear Polyurethane TubingTubing 1 2 OD 3 8 ID McMaster 4 Tube Adapter 10 32 UNF McMaster A Tube Adapter 3 8 NPT cMaster 97 0 75 7 20 5 gt m is WO op uJ oOJNJIJOJU U vla WO OlLO IN O 25 3 14 0 V 25 30 4 6 y i m V N WO WO V N O WO i O JD HD on r I
9. Thermoelectric devices are flat modules typically with approximate dimensions of 1 x1 x0 1 that use temperature differences between two surfaces to generate an output voltage The voltage output page l Copyright 2012 by the authors of a TE device is proportional to the temperature differential across the TE device as well as its dimensions Figures 1 and 2 show the construction and operation of TE devices Figure 1 Construction of a TE Device 1 CERAMIC f SUBSTRATE A P TYPE SEMICONDUCTOR PELLETS NEGATIVE CONDUCTOR TABS N TYPE SEMICONDUCTOR POSITIVE PELLETS Figure2 Operation of a TE Device 2 Heat Source TEGPower com Direction of Heat Flow Heat Sink Heat Dissipation Electrical Current Produced Advantages of TE devices include compactness solid state operation and modularity Because a huge proportion of waste energy comes in the form of heat thermoelectric technology has garnered much attention both in academia and in industry as a promising technology for capturing waste heat 1 3 Need for Performance Characterization Despite the promises of TE devices their low efficiencies limit their use in practical applications This limitation has led to active research in the field Currently novel thermoelectric materials and internal constructions of TE devices are being researched and developed to improve their performances and efficiencies Furthermore such research
10. alues Data presented in MEAM 446 2012 11 Figure 17 show comparison between test results obtained from TECLA s measurement of a TE device and published values from Hi Z 5 for their similarly dimensioned product Figure 17 Comparisons between TECLA Results and Published Value Dab poe ati tallied Pee eine eek e ATOT iit aca lok ateger rS E E whee CEES TI a nenat esa nn rn wn Voltage Output V anood be oda ssp epo odece s asooo sio odo ooa a Gem clea ae oeoo ele eee dam see aisle d bee biele db 6 oha e gasae o ohe sie oo ddo oha oie oa b o ohor A TECLA Measurements ene cea e a E cen Hi Z 2 TE Device Data 30 35 40 45 50 55 60 65 70 75 Temperature Difference deg C It should be noted the TE device used for testing was a generic non brand module with similar dimensions to the Hi Z 2 1 15 x 1 15 x 0 2 the voltage outputs of currently available TE devices with identical operating conditions depend almost exclusively on the dimensions because the materials used and the internal construction are similar across manufacturers Thus the results which are expected to be similar although not necessarily identical prove the reliability and accuracy of TECLA T DISCUSSION Overall TECLA s current design satisfies the basic requirements of a TE device characterization apparatus Particularly successful aspects include guaranteed surface contact with variable pressures e
11. ciples are identified and discussed in subsequent sections and the following three candidate design concepts were proposed to achieve them 3 1 1 Liquid Baths In this design a liquid container would be physically separated into two compartments i e a wall between the two liquid baths The temperature of each compartment would be controlled separately using a heating element for the hot side and a heat exchanger and a pump for the cold side In addition a blade mixer would be installed on each side to maintain uniform temperature in each liquid bath The two compartments would be insulated from each other but there would be a small fitting opening in the middle of the compartment such that a TE device could be placed inside the hole This would require good sealing and thermal insulation around the TE device Thus with this construction one side of the TE device would be exposed to liquid at high temperature and the other side would be exposed to liquid at a lower temperature page 2 Copyright 2012 by the authors 3 1 2 Applied Weights In this design a heating element with a solid flat surface would be used as heat source and forced convection cooling would be used for best heat rejection rate Heat transfer between the TE device surfaces and heat source heat sink is achieved by conduction through solid to solid surface contact In order to ensure sufficient heat transfer through uniform contact weights would be placed to
12. e for the user an enclosing box made of acrylic was laser cut and attached to the wooden base with a steel hinge Figure 10 shows the assembly of these machined components page 6 Copyright 2012 by the authors Figure 10 Easy Access to TE Device 5 3 Thermal Grease for Heat Transfer During our prototype fabrication we learned the importance of thermal grease for effective heat transfer For instance the heat rejection rate of the heat sink is significantly improved by application of thermal grease within its assembly Figure 11 exemplifies the strong effect thermal grease had on TECLA s performance Figure 11 Effect of Thermal Grease on Heat Sink Performance Without Thermal Grease With Thermal Grease Cold Side Temperature deg C Time Without thermal grease the maximum temperature and rate of temperature increase of the cold side were significantly greater than analogous values with thermal grease applied Using thermal grease cold side temperature varied only 1 2 degrees Celsius during the length of a test even when hot side temperature exceeded 100 degrees Celsius Thus for effective heat transfer thermal grease was applied at every contact interface MEAM 446 2012 11 5 4 Contact Pressure For TECLA a pneumatic actuator was installed to apply a constant pressure on the TE device with a precisely machined flat aluminum piece that was mounted to the end of the actuator This ensures an even distrib
13. ently the reading on the pressure gauge is taken as the pressure applied on the TE device A direct measurement at the point of mechanical contact would provide a more accurate measurement of this pressure Second power output and efficiency in addition to voltage output may be measured by adding modular variable load resistances Both of these additions can be implemented with relative ease and simplicity and will make TECLA which is already fully functional in its current construction more comprehensive in its ability to characterize TE device performance 9 REFERENCES 1 Scansen Don Thermoelectric Energy Harvesting Digi Key Web 23 Apr 2012 lt http www digikey com us en techzone energy harvesting resources articles thermoelectric energy harvesting html gt 2 Thermoelectric Generator Thermoelectric Generator Web 23 Apr 2012 lt http www tegpower com gt 3 Ciylan B and S Yilmaz Design of a Thermoelectric Module Test System Using a Novel Test Method International Journal of Thermal Sciences 46 7 2007 717 25 Web 4 Zou Mingging Boming Yu Jianchao Cai and Peng Xu Fractal Model for Thermal Contact Conductance Journal of Heat Transfer 130 10 2008 101301 Web 5 Hi Z 2 Thermoelectric Module Hi Z Technology Inc Web lt http hi z com documents Hi Z_Module_Properties xls gt MEAM 446 2012 11 page 10 Copyright 2012 by the authors APPENDIX A MATERIALS AND CO
14. fficacy of heat sink and heat source to create large temperature differentials usability of entire device ease of swapping in out TE devices set up of test GUI etc and accuracy and reliability of measurements Although the fundamental mechanism behind the characterization is quite straightforward and not novel to both industry and academia there had been no testing instruments available for use in research It is in fact unclear how TE device performances are reported by manufacturers The testing procedure for TE device performances are largely unreported therefore many reports of TE device performances seem vague and to a certain extent quite arbitrary TECLA is a successful example of a custom built lab apparatus for TE device characterization In addition in this paper we have reported the construction of the machine measurement techniques and verifications of TECLA Therefore we believe TECLA is a successful example of design and implementation of an integrated system for researchers who need reliable and consistent characterization of TE devices page 9 Copyright 2012 by the authors 8 CONCLUSIONS AND RECOMMENDATIONS TECLA successfully fulfills the requirements laid out for this project However for more comprehensive performance characterization we suggest two additions modifications that can be made to the system First a precise measurement of the pressure load applied by the actuator may prove useful Curr
15. gy Compressed Controls Actuator Pneumatic Air Actuator Contact Pressure PC MATLAB Coolant Liquid Cooling System Heat Sink Thermocouple 2 amp 3 Temperature Measurement Microcontroller Thermocouple 1 Heat Source Voltage Measurement Microcontroller Vie generated aAT MEAM 446 2012 11 1 INTRODUCTION AND BACKGROUND 1 1 Motivation In today s energy intensive world reducing energy consumption is seen as a vitally important task Energy generation not only has economic implications but also impacts the environment In the U S 94 6 quads quadrillion BTUs of energy were used in 2009 Of this approximately 54 64 quads or 58 of the total energy use were lost as rejected energy Although some magnitude of energy loss due to machine inefficiencies is inevitable due to fundamental laws of thermodynamics there has been much research in reducing the magnitude of losses by improving machine efficiency Another way to reduce energy consumption is to capture and make use of the rejected energy which would otherwise be dissipated into the surroundings without being used for any useful purposes Thermoelectric generation is one emerging technology used to capture rejected energy 1 2 Thermoelectric Generators Thermoelectric generators use a phenomenon known as the thermoelectric effect to convert temperature differential i e heat into voltage
16. he op amp circuit revealed that it has an output range of OV to 30V and an accuracy of 0 2V The Phidget voltage sensor has a range of 30V to 30V with a maximum error of 0 6V The total accuracy of the voltage measurement is therefore 0 8V After scaling it down the accuracy is within 0 09V 5 7 _ Data Collection and Processing Both temperature and voltage data are collected by corresponding microcontrollers and sent to the MATLAB program When starting a test the Graphical User Interface GUI provides the user with two options 1 start test and stop when all readings stabilize 2 start test and stop manually as shown in Figure 15 During a test the GUI displays hot and cold temperatures temperature difference and voltage readings in real time At the end of each test the GUI produces plots that help the user visualize the performance of the TE device One of the plots produced is voltage output as a function of temperature difference which shows the direct relationship between temperature difference and voltage Another plot is temperatures and voltage as a function of time which allows the user to evaluate the transient behavior of the TE device In addition the GUI saves all temperature and voltage data as a out file for access in the future The GUI code is relatively simple and can be easily modified by experienced MATLAB users page amp Copyright 2012 by the authors Figure 15 TECLA s GUI e890 lt Stude
17. ing the pressure applied on the TE device and subsequently measuring the output voltage page 3 Copyright 2012 by the authors Figure 4 Dependence of Voltage Output on Applied Pressure Pressure Applied on TE Device psi The test of variable weights on the TE device displayed an asymptotic behavior suggesting a minimum pressure was required to achieve optimal results The optimal weight may vary depending on the TE device stressing the importance of a variable pressure supply Pressure dependence can be explained by the microscopic surface imperfections seen at the interface between the TE devices and heat sources Small voids filled with air create a high thermal resistance which decreases the heat transferred from the heat source to the heat sink through the TE device This phenomenon is illustrated in Figure 5 4 Figure 5 Schematic of Micro Scale Surface Roughness and Asperities Voids filled with air act as an insulator Blue arrows Peltier Module 4 3 __ Small Voltage Measurement Accuracy and high resolution are desirable characteristics for a lab apparatus This is especially important for voltage measurement for TECLA because of the small order of magnitude of the voltage that is produced by TE devices For accurate measurement the resolution of the measurement device must be finer than the change in voltage output between consecutive measurements This was initially deemed feasible with a commercia
18. lly available high precision voltage sensor and a corresponding microcontroller However during our prototype realization MEAM 446 2012 11 this turned out to be false in section 5 of this paper we discuss additional instrumentation that was implemented to meet this requirement 4 4 _ _Temperature Measurement In order to characterize TE devices accurately precise and accurate measurements of hot and cold side temperatures of the TE device must be obtained This goal was achieved by placing an aluminum block with thickness 0 25 above the hot plate and below the heat sink These aluminum conduction blocks transfer heat from the heat source across the TE device and into the heat sink They also allow easy temperature measurements at the surfaces of the TE device Temperatures at the surfaces of the TE device were measured by placing thermocouples inside slots on both conduction blocks Analytical calculations showed that temperature measurements inside the block are sufficiently accurate to measure the temperatures at the surfaces of the TE device The calculation done for the conduction block for the hot side is shown below 0 25 in TE module conduction block surface ii hot plate q Dimensions e Aluminum block thickness L 0 25in 0 00635m e Thermal conductivity k 237 W m K Assumptions e Perfect contact between the aluminum block and the hot plate due to application of thermal grease e Temperature of the h
19. movement of the heat sink unit The slider had two drilled out through holes that were fitted with linear bearings to enable smooth vertical movement along the aluminum shafts used as guide rods Diagrams of the machined parts shaded areas are shown in Figure 9 Figure9 Schematic Diagrams of Custom Machined Parts aluminum bar to secure heat sink acrylic plate machined heat sink copper plate aluminum mount MEAM 446 2012 11 hinge machined slider heat sink mount aluminum shaft holes fitted with linear bearings Aluminum conduction blocks were machined to allow for temperature measurements near the TE device surfaces These blocks were machined with the finest possible surface finish for optimal heat transfer capabilities Each conduction block had 1 deep 1 diameter holes drilled into the sides so that thermocouples could be inserted for temperature measurement All of TECLA s components were assembled and combined on a wooden base Wood was selected due to its low cost light weight high durability and aesthetic qualities The most challenging task at this stage was attaching the two aluminum shafts so that the heat sink unit would be able to slide seamlessly along these shafts After much consideration the shafts were tapped and screwed into the wooden base with wood insert screws This method was chosen to ensure that the shafts remained as vertical as possible In order to make TECLA saf
20. nt Version gt GUI MATLAB User Interface for TECLA Real Time Data Hot Side Temperature deg C T_H Cold Side Temperature deg C Measurement 1 T_C1 Measurement 2 T_C2 Temperature Difference deg C T_diff Voltage Output V V CONNECTING Run Until Stable T amp V Run Until Manual Stop Stop 6 EVALUATION AND TEST Multiple tests were conducted to ensure reliability and accuracy of TECLA Voltmeter measurements of output voltage to check consistency of TECLA measurements were used as a first order verification Additionally the TE device was connected to an oscilloscope to verify accuracy of previous TECLA measurement data Both tests verified the accuracy of TECLA voltage measurements Also important to the viability of any test apparatus is repeatability Multiple tests using the same TE device under identical conditions were conducted to check for similar results TECLA proved repeatable as measured values of voltage under identical operating conditions never deviated more than 20mV or 3 Results of successive tests are presented in Figure 16 Figure 16 Repeatability Tests Voltage Output v 40 20 30 40 50 60 70 Bo Temperature Difference deg C Finally results from published values for TE devices were compared to tests from TECLA High end suppliers of TE devices provide data for their products allowing direct comparison between test results of open circuit voltage from TECLA and known v
21. ot plate Tylate 250 C e Power input of the hot plate q 1000 Watts e Steady State e Heat only flows in the vertical direction e Slot for the thermocouple is very small compared to the aluminum block k q L WU aine Lian 237 1000 250 T 0 00635 TE hot x 0 0 00635m thickness of conduction block and when x 0 006357 T aapa 9I TPC Temperature distribution of the aluminum conduction block is shown as T x below page 4 Copyright 2012 by the authors T T plate TE hot POS ge late T x 250 4 72x x 0 0 00635m Note x 0 at the hot plate and x 0 00635m at the surface of the TE device Therefore the temperature difference between the hot plate surface and the TE device surface is negligible at only 0 03 degrees Celsius 4 5 __ User Friendliness and Safety A fundamental requirement for TECLA was the facility with which TE modules could be swapped in and out In order to achieve this goal a design that allowed the user to lift the heat sink unit and easily place a TE device below it was implemented The heat sink unit was retrofitted to a custom machined aluminum holder that allowed for a hinge to be attached to it such that the user would be able to open and close the unit to place and remove a TE device Figure 6 shows a diagram of this mechanism Figure6 Opening and Closing of Retrofitted Cooler Unit When testing a TE device using TECLA a significant amount of
22. rate of heat rejection Figure 7 Integrated Cooling Unit with Heat Exchanger and Pump A pneumatic actuator along with a set of valves is actuated by compressed air to apply uniform contact pressure on the TE device Thermocouples are used to measure the temperatures of both the hot and cold sides of the TE device A precision voltage sensor with appropriate circuits is used to measure the voltage Both temperature and voltage data are collected by corresponding microcontrollers and sent to the PC Finally a MATLAB program stores the data for further processing while providing a user friendly interface for the control of the apparatus page 5 Copyright 2012 by the authors Figure8 Final Assembly of TECLA 5 2 Manufacturing of Components A number of components were custom machined for TECLA First in order to integrate a commercially available heat sink unit into TECLA s assembly a multi part mount was machined The mount consisted of an aluminum tray 4 x 5 with a rectangular slot cut out to expose only the copper plate of the heat sink unit when placed on the TE device An aluminum fastener was machined to secure the top of the heat sink unit to the aluminum tray An acrylic plate 6 x 6 was designed and laser cut to accommodate the mount and heat sink assembly an aluminum counterweight handle and a steel hinge The other end of the hinge was attached to a slider machined to facilitate the vertical
23. the output voltage was amplified before being read by the voltage sensor The voltage was then scaled down in the MATLAB program The voltage outputted by the TE device was run through an operational amplifier op amp circuit shown in Figure 13 and amplified by a factor of R2 R1 Using an LM358 op amp and two 100k ohm and 15k ohm resistors the voltage was amplified by approximately 6 7 This gain was decided by the voltage range produced by TE device and the op amp voltage supply The op amp cannot amplify a voltage beyond its supply voltage Hence the amplified voltage could not exceed 30V The maximum recorded value of TE voltage output was approximately 2 2 volts With an amplification of 6 7 this provided a safety factor of 2 0 Figure 13 Op Amp Circuit Used for TECLA Ry out Ideally the amplification should be R2 R1 but in actuality the amplification includes a gain and an offset Data points were gathered by inputting known voltages into the circuit and measuring the output voltage The relationship is linear With a linear fit the gain slope of the line and the offset y intercept were found and accounted for in the MATLAB code The data used for this calibration is plotted in Figure 14 MEAM 446 2012 11 Figure 14 Calibration of Op Amp Amplified Voltage VV J 0 5 1 15 2 2 5 3 Input Voltage V The accuracy of voltage measurement is affected by the Op amp circuit and the voltage sensor Calibration of t
24. ution of pressure over the TE device surface area during tests Figure 12 shows the schematic diagram of the pressure system The 2 way pneumatic actuator has two inputs one of which extends the shaft while the other retracts it The three way valve directs compressed air from a single source into the appropriate input port to either extend or retract the actuator shaft Figure 12 Configuration Used for Contact Pressure Schematic and Picture 2 way pneumatic actuator 5 5 _ Temperature Measurement Hot and cold side temperatures are measured with K type Phidget thermocouples They have a range of 50 degrees Celsius to 450 degrees Celsius and an accuracy of 0 75 degrees Celsius Typical noise of 0 02 degrees Celsius found in the Phidget temperature sensor accounts for some of the error in the data 5 6 _ Small Voltage Measurement Output Voltage Amplification After the TECLA prototype was initially assembled the voltage measurement exhibited a stepping effect in which the voltage remained at a certain level for a length of time and then jumped to another level instantaneously Further page 7 Copyright 2012 by the authors investigation revealed that the precision voltage sensor used to measure the voltage had a resolution of 0 07 volts The change in voltage with each measurement was too small for the voltage sensor to detect In order to ensure that even the smallest changes in voltage could be recorded
25. wer supply into lead labeled Power in coming out of circuit box Be sure to plug appropriate power ground into the leads failing to do so will BREAK the OP AMP 6 Connect the 2 USBs coming out of circuit box into laptop desktop 7 Open MATLAB and change to appropriate directory where GUI and corresponding files are saved 8 Type GUI in command window to run the GUI and initialize all parameters 9 Close box of TECLA and secure latches 10 With compressed air supply connected to actuator turn 3 way valve to position labeled OUT This will extend the actuator Make sure to pull the release valve of whatever line you are NOT supplying air to this releases residual pressures from previous use of the actuator Amount of pressure can be controlled via the compressed air supply 11 Power on cooler to desired pump and fan speeds speeds vary from 1 10 and are controlled using buttons on the cooler 12 Power on hot plate to desired temperature 13 Start taking measurements using GUI Select desired option to manually stop or run until stable 14 Once test is complete power off all units 15 To retract the actuator turn the 3 way valve to position labeled IN Ifit does not retract pull release valve of OUT line to get rid of residual pressure in the tubing Note Current MATLAB code was run on 32 bit version There have been issues running the GUI on the 64 bit version of MATLAB The current code has not
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