Lecture 2 basic electricity
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Lecture #2 Basic Electricity. 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!!!. Basics. Electricity is the flow of electrons

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Lecture #2 Basic Electricity

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Lecture 2 basic electricity

Lecture #2 Basic Electricity


Why learn electronics

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!!!


Basics

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


Lecture 2 basic electricity

  • A complete circuit is required for current to flow

  • Also required:

    • A source of “pressure” (voltage)

  • Optional:

    • Switch

    • Something to do work


Terms

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)


Terms cont

Terms (cont)

  • Resistance: the resistance to flow

  • Friction in the pipe

  • Units

    • Ω – Ohm

  • Symbol

  • -WW-


Simple equations

Simple Equations

  • Ohm's Law

    E=IR

    • E– Voltage (volts)

    • I – Current (amps)

    • R – Resistance (ohm)

  • Power

    P=IE

    • Watts


  • Components resistors

    Components: Resistors

    • Electronic component that provides resistance to the flow of electrons

    • Come in variety of sizes and ability to handle power


    Resistors

    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


    Using resistors

    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


    Special resistors

    Special resistors

    • Variable resistor: 2 terminals

    • Examples

      • Audio control

      • Joysitck

      • Rheostat

  • Potentiometer: 3 terminals

    • Voltage divider


  • Diodes

    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


    Diodes1

    Diodes

    • Used to separate battery packs

    • Also used to “idiot proof” connections

    • Called “diode isolation”

    • More later….


    Diodes2

    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


    Capacitors

    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……


    Capacitors1

    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


    Lecture 2 basic electricity

    • Using capacitors:

    • Absorb voltage spikes


    Multimeters

    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


    Dc vs ac

    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


    Dc vs ac1

    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/


    Dc vs ac2

    DC vs AC

    http://electronicsprojects.mediadir.in/category/hobby-circuits/page/84/


    What is electro magnetism

    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.


    All magnetism is related to electricity

    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.


    Lecture 2 basic electricity

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


    Lecture 2 basic electricity

    • Or, you can rotate a wire inside a magnetic field.

    • Generators and alternators


    Electromagnetism

    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


    Lecture 2 basic electricity

    • 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


    Switches

    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.


    Relays

    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)


    Relay applications

    Relay applications

    • Cars

      • Horn

      • Lights

      • Starter

    • Ocean:

      • Sensor power

      • Burn wires

      • Controller power

      • motors


    Transistors

    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


    How transistors work don t sweat the details

    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


    Typical transistor circuit

    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


    Analogue signal

    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


    Digital signal

    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


    Analog to digital conversion

    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”


    Communications types

    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


    Instruments require power

    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?


    Powering marine instrumentation

    Powering Marine Instrumentation

    • Two main options

      • Batteries

      • Sea cable

        • Power from ship or shore

        • Usually allows data to be “Live Feed” as well


    Sea cables

    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


    Sea cables1

    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


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