Power MeterTeamMotivationProblem StatementDesign RequirementsSlide 6Digital Power MeasurementVoltage-Sensing CircuitSimulationSimulation ResultsMonte Carlo SimulationCurrent-Sensing CircuitSlide 13Slide 14Slide 15A/D ConversionPower Factor CalculationC Program FlowUMPS SimulationSlide 20Conclusions/Future WorkReferencesReferences (cont.)Slide 24Power MeterPower Meter ECE 4512 Senior Design IDepartment of Electrical & Computer EngineeringMississippi State UniversityTeamTeamAdvisor:Professor Raymond S. WintonTeam Leader:Wei-Keat QuekContribution: A/D Converter, LCD Display, & DocumentationTeam Members:Matthew HemphillContribution: Voltage-sensing circuit & DocumentationScott FredrickContribution: Current-sensing circuit & DocumentationJames NixonContribution: Microcontroller & DocumentationMotivationMotivationTo provide average American householders with a portable & accurate digital power meter•Importance–Can educate consumers, save them money, & aid in purchase decisions–Can aid in troubleshooting problem circuits & in making decisions to conserve energy •Relevance–Allows for concrete, practical design experience based on curriculum–Allows for group collaboration and division of tasks based on each member’s specialtyProblem StatementProblem Statement•To accurately sense the voltage and current used over a range of typical household devices.•To achieve reliable power measurements by taking phase differences between the voltage and current, i.e. the power factor, into account.Design RequirementsDesign Requirements• Voltage-sensing circuit (0 to 120 Vrms)• Current-sensing circuit (0 to 30 A)• Power Factor Calculation (DS87Cx20 Microcontroller)• Power (9 V Battery)Design RequirementsDesign Requirements• Display (4-digit LCD)• Power Measurement Range (0 to 3600 W)• Energy Measurement Range (0 to 86.4 kWhrs)• Tolerance (+/- 3%)• Size & Packaging (Plastic enclosure –4” x 8” x 1.5” (W x L x D))Digital Power Digital Power MeasurementMeasurementVoltage-Sensing CircuitVoltage-Sensing Circuitvo = (1 + 2*R4/R3)(v2 – v1)where = R2/R1SimulationSimulationSimulation ResultsSimulation ResultsVoltage Input (Vp-p) Vo (Vp-p) Vo Scaled by 36 Percent error (%)180 5.0110 180.396 0.2200170 4.7227 170.017 0.0101160 4.4322 159.559 0.2755150 4.1637 149.893 0.0712140 3.9022 140.479 0.3423130 3.6260 130.536 0.4123120 3.3447 120.409 0.3410110 3.0547 109.409 0.0280100 2.7774 99.9864 0.013690 2.5067 90.2412 0.2680Monte Carlo SimulationMonte Carlo SimulationCurrent-Sensing CircuitCurrent-Sensing CircuitSimulationSimulationSimulation ResultsSimulation ResultsVoltage Input (Vp-p) Vo (mVp-p) I (mA) I (Rsense) (mA) Percent error (%)180 68.743 68.743 68.714 0.0422170 64.775 64.775 64.803 0.0432160 61.459 61.459 61.433 0.0423150 57.585 57.585 57.587 0.0035140 52.740 52.740 52.717 0.0436130 48.959 48.959 48.935 0.0491120 46.029 46.029 46.001 0.0608110 42.131 42.131 42.092 0.0927100 37.895 37.895 37.872 0.060790 34.303 34.303 34.280 0.0671Monte Carlo SimulationMonte Carlo SimulationA/D ConversionA/D ConversionPower Factor CalculationPower Factor CalculationSampling & Displacement • Sampling rate >= 1/(8*fo) where fo = 60 Hz• Displacement = -/ where = 2fExample• = * displacement = 2(60 Hz)*1.5 ms = 0.565 rad/sPower• P = Vrms*Irms*cos() = (127.6 V)/(68.714 mA)(0.8446) = 7.4 WMaclaurin Series• cos() = 1 - ^2/2! + ^4/4! - ^6/6! + … + (-1)^k ^2k/2k! + …C Code•After the first three harmonics, cos () = cos(0.565) = 0.8446.C Program FlowC Program FlowStartSelect functionReceive digital voltage value(Reference)Receive digital current valueHas first zero-crossing been reached?Calculate displacement between current and voltageCalculate real powerTime out or disconnect?Display outputEndInput timePinstantaneousPavgNoYesNoYesUMPS SimulationUMPS SimulationP1.6P1.7 P3.0-P3.7EA P2.1P2.2Vcc XTAL1GND XTAL2LCDDS87Cx20VccVcc0.1 F30 pF30 pF4 MHzSW2SW13110 K204023722191810-1785/17-146432UMPS SimulationUMPS SimulationCPU RegistersSW2SW17SP07ResourcesP10000003FP300000007org 0 ajmp Main org 020h ; Program MainMain: mov CKCON,#%00001000 ; Use Internal /4 Clock for Timer0 mov TMOD,#%00000001 ; Timer0 - Uses Internal Clock ; - Run in Mode 1 mov TCON,#%00010000 ; Start Timer0 running mov IE,#%10000010 ; Enable the Timer 0 Interrupt; LCD Display mov P1,#03Fh ; Make sure all LCD lines are Low acall Dlay5 ; Wait 15 ms for the Display to Power Up acall Dlay5 acall Dlay5 mov P3,#$7 ; Output a 7 on the Display Line clr P1.6 ; Clear the RS Line setb P1.7 ; Toggle the LCD "E" Clock clr P1.7 acall Dlay5 ; Wait 5 ms for the instruction to execute :c:\temp\lcd.asmConclusions/Future WorkConclusions/Future WorkConclusions•Ensure our tolerance levels are met•Meet challenge of accuracyFuture Improvements•Expand functions for both AC & DC measurements•Expand measuring range•Improve tolerance levels•Allow PC connectivity•Improve internal power consumptionReferencesReferences[1] “ADC 0801/ADC 0802 ADC 0803 ADC 0804 ADC 0805 8 bit µP Compatible A/D Converters”, National Semiconductor Corporation, U.S.A., 2000. [2] “EDC190 4-Digit 7-Segment Liquid Crystal Display”, Microelectronic Company, U.S.A., June 1987.[3] Fisher, G. J., “An Enhanced Power Meter for SPICE2 Circuit Simulation,” IEEE Transactions On Computer-Aided Design, Harris Semiconductor, Melbourne, FL, May, 1998.[4] Garverick, S. L., McGrath, D. T., Baetsch, R. D., and Fujino, K., “A Programmable Mixed-Signal ASIC for Power Metering,” IEEE International Solid-State Circuits Conference, GE Corporate Research and Development, Schenectady, NY, January, 1991.[5] Graf, Rudolf F., Encyclopedia of Electronic Circuits, Vol. 3, TAB Books Inc., 1991.[6] Hanselman, Duane, and Littlefield, Bruce, Mastering MATLAB: A Comprehensive Tutorial and Reference, The MATLAB Curriculum Series, Upper Saddle River, NJ: Prentice Hall, 1996.[7] Hayes, Thomas C., and Horowitz, Paul,
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