Power MeterTeamProblem StatementDesign RequirementsDigital Power MeasurementVoltage-Sensing CircuitSlide 7Voltage-Sensing Circuit (cont.)Slide 9Current-Sensing CircuitPreliminary Hardware TestsPower Factor CalculationMilestone ChartConclusions/Future WorkPower MeterPower Meter ECE 4522 Senior Design IIDepartment of Electrical & Computer EngineeringMississippi State UniversityTeamTeamAdvisor:Professor Raymond S. WintonTeam Leader:Matthew HemphillContribution: Voltage-sensing circuit & DocumentationTeam Members:Wei-Keat QuekContribution: A/D Converter, LCD Display & DocumentationScott FredrickContribution: Current-sensing circuit & DocumentationJames NixonContribution: Microcontroller & DocumentationProblem 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.•To ensure our tolerance levels are met.•To construct the finished product within our cost estimates.Design RequirementsDesign Requirements• Power Factor Calculation (PIC16F877 Microcontroller)• Power (9V Battery) • Power Measurement Range (1 to 1800 W)• Energy Measurement Range (1 to 43.2 kWhrs)• Tolerance (± 3%)• Size & Packaging (Plastic enclosure – 4” x 8” x 1.5” (W x L x D))• Voltage-sensing circuit (0 to 120 Vrms)• Current-sensing circuit (0 to 15 Arms)Digital Power Digital Power MeasurementMeasurementComponentsBasic Functionality TestedNormal Working Conditions TestingDebuggingVoltage Sensing Circuit•Current sensing Circuit•A/D Converter• •Microcontroller• •LCD Display • •Voltage-Sensing CircuitVoltage-Sensing CircuitInput Simulated Output Circuit Output120 Vrms 0.8487 Vrms 0.8572 VrmsVoltage-Sensing CircuitVoltage-Sensing CircuitVoltage-Sensing Circuit (cont.)Voltage-Sensing Circuit (cont.)Voltage Input (Vp-p) Vo (Vp-p) Vo Scaled by 36 Percent error (%)180 1.2692 179.97 0.0152170 1.1981 169.89 0.0644160 1.1308 160.35 0.2172150 1.0611 150.46 0.3093140 0.9908 140.49 0.3539130 0.9200 130.45 0.3461120 0.8486 120.33 0.2750110 0.7763 110.08 0.0727100 0.7028 99.66 0.343090 0.6327 89.72 0.3144Voltage-Sensing Circuit (cont.)Voltage-Sensing Circuit (cont.)Current-Sensing CircuitCurrent-Sensing CircuitLoad Current Simulated Output Circuit Output3.452 A 3.417 V 3.41 VPreliminary Hardware Preliminary Hardware TestsTestsDeviceWall VoltageVoltage Circuit OutputScaled OutputLoad CurrentCurrent Circuit Output30 W Soldering Iron120.25 V 3.343 V 113.67 V 259 mA 250.6 V100 W Light Bulb119.91 V 3.328 V 113.15 V 0.856 A 0.829 V200 W Light Bulb119.25 V 3.304 V 112.34 V 1.700 A 1.657 V400 W Work Light118.70 V 3.251 V 110.53 V 3.452 A 3.41 VPower 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/s• P = Vrms*Irms*cos() = (127.6 V)/(68.714 mA)(0.8446) = 7.4 WSoftware• Continuously poll two inputs separate from A/D inputs• Test for first zero value of voltage and begin timer• Test for first zero value of current and stop timer• If Time = Period, then the signals are in phaseMilestone ChartMilestone ChartSenior Design I (Fall ’00) Week 2 Problem Statement & Requirements Document Week 5 Test Specification Document Week 7 Preliminary Design Review Week 11 Test Certification Document Week 13 Design Document Week 14 Design Review Week 16 Web SiteSenior Design II (Spring ’01) Week 5 Preliminary Hardware Review Week 6 Preliminary Design Review Week 12 Hardware Test Verification Week 13 Design Document Week 14 Design Review Week 16 Web SiteConclusions/Future WorkConclusions/Future WorkConclusions•The Power Meter measurement ranges had to be refined.•The hardware tests showed comparable results to the simulations.Future Work•Interface all the circuits to a single-board prototype.•Refine power factor calculation.•Implement user
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