Common Electrical Components in Oceanographic SystemsReviewing BasicsThe Op-AmpSerial CommunicationsPulse Width ModulationSome PWM UsesField Effect Transistor (FET)The Basic DC Brush MotorProperties of the DC Brush MotorIncremental EncodersStepper MotorsEmbedded MicroprocessorsMajor Issues with Embedded Microprocessor (EMB) ApplicationsDigital to Analog Conversion (D/A)Analog to Digital Conversion (A/D)What is the Onset TattleTale Model 8?Power Sources for Marine SystemsCharacteristics of Power Systems for Marine ApplicationsThis LectureOtto and Diesel CyclesLM2500 Specifications - QuotedBattery TechnologiesOverall Discharge Dependence on Current and TemperatureComparison of Battery Performance for Mobile ApplicationsFuel CellsSome Fuel Cell IssuesState of the Art 2005ReferencesMassachusetts Institute of Technology 12.097Common Electrical Components in Oceanographic SystemsMassachusetts Institute of Technology 12.097Reviewing Basics• Kirchoff’s Voltage rule: voltages V at a node are the same.• Kirchoff’s Current rule: sum of currents i flowing into and out of a node is zero.• Analogy: Voltage is like fluid pressure, current is like fluid volumetric flow rate. The wire is like a pipe.• Resistor R: V = IR, – Dissipation: Resistive Power P = I2R = V2/R– Analogy: viscous losses in pipe flow• Capacitor C: i = C dV/dt– Analogy: a hydraulic accumulator• Inductor H: V = L di/dt– Analogy: inertia of water in a pipeOhms, Ωfarads, fhenries, hMassachusetts Institute of Technology 12.097The Op-AmpTwo inputs (called inverting and non-inverting); one output.The output voltage is a HUGE gain multiplied by the difference between the inputs.Horiwitz’s & Hill’s golden rules: a. The op-amp enforces (in proper use) Vinv= Vnon-invb. No current flows into the device at either inputVinvVnon-invV+ (supply)V- (supply)VoutMassachusetts Institute of Technology 12.097Example Op-Amp: Adding a Voltage BiasR2(V-Vinv)/R1= (Vinv-Vout)/R2andVinv= Vnon-inv VR2= Vinv(R1+R2) – VoutR1Vout= Vnon-inv(R1+ R2)/R1–VR2/R1Letting R1 = R2, thenVout= 2Vnon-inv–VThe circuit inverts the input V and adds on 2Vnon-invIF Vnon_invis ground, then Voutis –V. This is just an inverting amplifier.VinvVnon-invV+V-R1VVoutVoltage bias useful for bringing signal levels into the range of sensors.The op-amp is discussed in detail by Horowitz and Hill, covering integrators, filters, etc.Massachusetts Institute of Technology 12.097Serial Communications• How to transmit digital information fast and reliably over a few wires?• Examples: RS-232, RS-485, etc. refer to pins & wires• A minimal case of RS-232 (DB25 connector is full case):– Asynchronous operation; both sides agree on BAUD rate– Three wires: send (TX), receive (RX), ground– No error checking! No flow control!EXAMPLE using CMOS components:64 + 32 + 1 = 97 = ‘a’Start bitnormally high11 100000Stop bitSuccessive bits read at midpoints, based on baud rate and on start bit leading edge5VGND32’s1’s(LSB)2’s 4’s 8’s 16’s 64’s 128’s(MSB)Massachusetts Institute of Technology 12.097EXAMPLE: A GPS String• Garmin GPS25 series – Smart embedded device!• Similar to TT8’s interface with you – I/O strings are passed through a serial port• Reconfigurable through special commands• Output at 1Hz• String maintains exactlythe same syntax: e.g., $GPRMC,hhmmss,V,ddmm.mmmm,N,dddmm.mmmm,E,000.0,000.0,ddmmyy,000.0,E,N,*XX<CR><LF>73 chars appear as one line:$GPRMC,hhmmss,V,ddmm.mmmm,N,dddmm.mmmm,E,000.0,000.0,ddmmyy,000.0,E,N,*XXMassachusetts Institute of Technology 12.097Pulse Width Modulation• A Regular WaveformVolts VpeakPWM periodPulsewidth• PWM frequency (Hz) = 1 / PWM period• Duty cycle = Pulsewidth / PWM period• PWM frequencies typically range from 100Hz into MHz• Duty cycles can be used from 0 – 100%, although some systems use much smaller ranges, e.g. 5-10% for hobby remote servos.• The waveform has two pieces of information: Period and Pulsewidth, although they are usually not changed simultaneously.Massachusetts Institute of Technology 12.097Some PWM Uses• The Allure: very fast, cheap switches and clocks to approximatecontinuous processes. Also, two-state signal resists noise corruption.• Sensors: PWM period is naturally related to rotation or update rate: Hall effect, anemometers, incremental encoders, tachometers, etc. • Communication: PWM duty cycle is continuously variable  like an D/A and an A/D.• Actuation: At very high frequencies, physical systems filter out all butthe mean; i.e., Veffective= duty_cycle * VpeakHigh frequency switching is the dominant mode for powering large motors!Image removed for copyright reasons.Massachusetts Institute of Technology 12.097Field Effect Transistor (FET)• Like a “valve”, that is very easy to open or close. When FET is open, resistance is low (milli-Ohms); when FET is closed, resistance is high (mega-Ohms or higher)• Typically three connections:– Gate: the signal; low current– Source: power in– Drain: power out• N- and P-type junctions are common, and involve the polarity of the device. (N is shown)• Extremely sensitive to static discharge! Handle with care.• MOSFET: modern FET’s capable of handling higher power levels  PWM power.gateLoadSupply_++drainsource_Massachusetts Institute of Technology 12.097The Basic DC Brush MotorVector relations:force = current x fluxfield = velocity x fluxTorque τ  (coils)(flux density)(current i), or, in a given motor,τ= kt* i where ktis the torque constantBut the motion of the coils also induces a voltage in the coil, the back-EMF:eb= kt* ω (YES, that’s the same kt!)And the windings have a resistance R:eR= R * iSumming voltages around the loop,Vsupply= eb+ eRS Niτ, ωMassachusetts Institute of Technology 12.097Properties of the DC Brush Motor• No-load speed:τ= 0 i = 0  ω= V / kt• Zero-speed torque (BURNS UP MOTOR IF SUSTAINED):ω= 0 eb= 0 i = V / R  τ = ktV / R• Power output:Pout= τ ω= i ebPout= i ( V – Ri )• Efficiency:η = Pout / Pin= τ ω / i V  η= 1 - i R / Vτωτ= ktV/RPoint of maximum power: τ= ktV / 2 Rω= V / ktPoutdω/dτ = - R / kt2Massachusetts Institute of Technology 12.097Incremental Encoders• What is the position of the shaft?• Take advantage of cheap, fast counters  make a large number of pulses per revolution, and count them!• Advantages of the incremental encoder:–