Lecture #2 Basic Electricity

1. Lecture #2 Basic Electricity

2. Why learn electronics? • Ability to understand information sensor is providing • Be able to read a wring diagram • Basic understanding of what some components are doing in the circuit • Troubleshooting!!!

3. Basics • Electricity is the flow of electrons • Many similarities with the flow of water • Water flows because of a pressure difference • Bigger pipes allow more flow

4. A complete circuit is required for current to flow • Also required: • A source of “pressure” (voltage) • Optional: • Switch • Something to do work

5. Terms • Voltage • Electrical potential difference • Electrical “pressure” • Units • Volts (v) • Current • Flow of electron charge (phenomenon) • Rate of Flow of Electron charge (quantity) • Units • Ampere (A)

6. Terms (cont) • Resistance: the resistance to flow • Friction in the pipe • Units • Ω – Ohm • Symbol • -WW-

7. Simple Equations • Ohm's Law E=IR • E– Voltage (volts) • I – Current (amps) • R – Resistance (ohm) • Power P=IE • Watts

8. Components: Resistors • Electronic component that provides resistance to the flow of electrons • Come in variety of sizes and ability to handle power

9. Resistors • In Series • Resistance values (Ohms) add up to give total resistance • R1+R2+R3...=Rtotal • In Parallel • Each have same potential difference • 1/R1+1/R2...=1/Rtotal

10. Using resistors A • Voltage divider • Use Ohm’s law to calculate: • Current • Voltage between A and B • Voltage Between B and C • Assume: • R1 is 1000 Ω and R2 is 1000 Ω • R1 is 2000 Ω and R2 is 3000 Ω B C

11. Special resistors • Variable resistor: 2 terminals • Examples • Audio control • Joysitck • Rheostat • Potentiometer: 3 terminals • Voltage divider

12. Diodes • One-way valves • Allow current to flow in one direction • There is a drop in voltage across a diode • Drop is ~ 0.7V • Two main types • Single diode • Up to 100mA • Rectifier diode • Large Currents • Symbol

13. Diodes • Used to separate battery packs • Also used to “idiot proof” connections • Called “diode isolation” • More later….

14. Diodes • Light Emitting Diodes (LED) • Color is determined by the semiconductor material used • Still need to be connected in the correct direction • Current flow long to short • Easy to blow up • Limit voltage/current

15. Capacitors • Passive Electronic component • A pair of conductor separated by a dielectric • When a voltage is applied a charge builds up • Acts like a little battery • Why when you shut off certain things the light stays lit for a little even with no power • Eg. Computer power supply • Units: F - Farad • Symbol: -||- • Be very careful of very big ones……

16. Capacitors • In Series • The energy stored is equal to that of the other capacitors in the series • 1/C1+1/C2...=1/Ceq • In Parallel • Add up the capacitance • C1+C2+C3...=Ctotal • Opposite that of Resistors

17. Using capacitors: • Absorb voltage spikes

18. Multimeters • Tool used to test electronics (Main tool) • Voltage • Straight forward touch ends to terminals • Current • Need to put in sequence • Be sure you won’t exceed rating!!!! • Validity of a cable • “Ohm out” • Used to Identify the same wire in a cable

19. DC vs AC • Alternating Current (AC) • Polarity changes over time • Basic form is a sine wave • Other wave forms exist • Better for long distance transmission of power • High voltages – Low current • Pl=I2R • If current is doubled then 4x greater loss • Easily generated by a generator/alternator • Polarity changes as magnet spins • Can be “stepped up” and down using a transformer (more later) • Not used in Oceanographic instrumentation* • AC to DC converter almost always needed *Not often, anyway

20. DC vs AC • Direct Current (DC) • Unidirectional flow of electric charge • Sources • Batteries • Solar Panels • Used in low voltage applications • More complicated then AC • AC can be converted to DC • using a rectifier http://electronicsprojects.mediadir.in/category/hobby-circuits/page/84/

21. DC vs AC http://electronicsprojects.mediadir.in/category/hobby-circuits/page/84/

22. What is Electro-Magnetism? • Until 1821, only one kind of magnetism was known, the one produced by iron magnets. • Then a Danish scientist, Hans Christian Oersted discovered electromagnetism: • He noticed that the flow of electrical current in a wire caused a nearby compass needle to move. • The new phenomenon was studied in France by Andre-Marie Ampere, • He concluded that the nature of magnetism was quite different from what everyone had believed.

23. All magnetism is related to electricity • There thus exists two kinds of forces associated with electricity: • electric • magnetic. • In 1864 James Clerk Maxwell demonstrated a subtle connection between the two types of force • The connection involves the velocity of light. • From this connection sprang the idea that light was an electric phenomenon, • This led to the discovery of radio waves, the theory of relativity and a great deal of present-day physics.

24. A Changing magnetic field will “induce” a voltage.

25. Or, you can rotate a wire inside a magnetic field. • Generators and alternators

26. Electromagnetism • If you use one wire to generate a changing field (AC), it will induce voltage in a nearby coil • You can isolate circuits this way • Works through plastic, glass, aluminum, water • But AC will also induce noise into adjacent wires • Shielding helps • Twisting wires helps

27. The voltage induced is determined by the ratio of the number of winds on the coil • So you can step up or step down • Only with AC

28. Switches • Used to turn things on and off (duh!) • But come in lots of flavors: • Momentary • Toggle • Rotary • poles • SPST: single pole single throw • SPDT: Single pole, double through • DPST: double pole, single throw • DPDT: double pole, double throw • Etc.

29. Relays • Electrically operated switches • Generally use an electromagnet to close a switch • End result: use a small switch (limited current capability) to operate a larger switch (with larger current capacity)

30. Relay applications • Cars • Horn • Lights • Starter • Ocean: • Sensor power • Burn wires • Controller power • motors

31. Transistors • “relays” made of semiconductors • Used to control circuits • Used to amplify signals • Replaced vacuum tubes • Gazillions of them in a computer • We’ll learn later how they are used in digital logic

32. How transistors work(Don’t sweat the details) • Like two diodes back to back • No current can flow • But if you apply voltage to the middle layer, it ionizes (semi-conducts), allowing current through • More voltage = more flow • Variable “switch” • more like a valve

33. Typical transistor circuit • Apply voltage to Vin to make current flow • Note resistor • Combines with transistor to create a voltage divider • Result is using Vin to control Vout • But Vin may have VERY small voltage fluctuations while Vout has large fluctuations

34. Analogue Signal • Continuous signal • As that current changes the signal changes • Usually 0-5v, but can vary • Important when using analogue that your datalogger can handle the voltage produced by the sensor • Advantages • Infinite signal resolution • Can be processed by analog components • Disadvantages • Noisy • Shielded cable can help diminish the noise • Subject to loss in cables and connectors

35. Digital Signal • Non-continuous signal • Two amplitude levels called nodes • Digital logic • 0 or 1 • True or false, yes or no, on or off • Fixed number of digits or bits • Sent as binary and needs a program to convert to “readable” values

36. Analog to Digital Conversion • All analogue signals are converted to digital for processing • Resolution of the data depends on the A/D converter used • Signal is placed into bits • Stored in binary • Example – 12bit A/D converter • Range 0-5v • A/D resolution 12bits: 212 =4096 quantization levels • Analog voltage resolution is: 5V/4096 • Meaning each “level” is equal to ~1.22mV/“level”

37. Communications types • Analogue • Direct signal • Digital • Serial • RS 232 • Most common • 15m max length • 20kbs max speed • RS 485 • 1200 max length • 100kbs @ 1200m • 35 Mbs @ 15m • Parallel: almost obsolete • Ethernet • Large data transfer

38. Instruments require Power • No Power No data • All sensors require power to operate, some more than others • How long with the sensor last? • How many sensors can I run off one datalogger? • Which batteries should I go with? • Rechargeable or primary (one time use) • How many batteries do I need?

39. Powering Marine Instrumentation • Two main options • Batteries • Sea cable • Power from ship or shore • Usually allows data to be “Live Feed” as well

40. Sea Cables • DC Power from ship • Usually 12-15 volts • Power limited due to: • Slip rings • Distance • Surface power supply • Usually not limited by voltage • Depends on what is at the other end of the cable for interfacing the sensor • Majority of ship deployment setups use Sea Cables

41. Sea Cables • What if your sensor requires more power or higher voltage • Use a battery • but data may still be able to be sent up the sea cable • What if the ship only has one sea cable? • (Usually hooked to the CTD) • Bring your own sea cable • Use a battery