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# Lecture #2 Basic Electricity - PowerPoint PPT Presentation

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

• 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!!!

• 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

• 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)

• Resistance: the resistance to flow

• Friction in the pipe

• Units

• Ω – Ohm

• Symbol

• -WW-

• Ohm's Law

E=IR

• E– Voltage (volts)

• I – Current (amps)

• R – Resistance (ohm)

• Power

P=IE

• Watts

• Electronic component that provides resistance to the flow of electrons

• Come in variety of sizes and ability to handle power

• 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

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

• Variable resistor: 2 terminals

• Examples

• Audio control

• Joysitck

• Rheostat

• Potentiometer: 3 terminals

• Voltage divider

• 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

• Used to separate battery packs

• Also used to “idiot proof” connections

• Called “diode isolation”

• More later….

• 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

• 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

• Symbol: -||-

• Be very careful of very big ones……

• In Series

• The energy stored is equal to that of the other capacitors in the series

• 1/C1+1/C2...=1/Ceq

• In Parallel

• C1+C2+C3...=Ctotal

• Opposite that of Resistors

• 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

• 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

• 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

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.

• 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.

• 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

Switches of winds on the coil

• 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 of winds on the coil

• 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 of winds on the coil

• Cars

• Horn

• Lights

• Starter

• Ocean:

• Sensor power

• Burn wires

• Controller power

• motors

Transistors of winds on the coil

• 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 of winds on the coil(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 of winds on the coil

• 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 of winds on the coil

• 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

• Infinite signal resolution

• Can be processed by analog components

• Noisy

• Shielded cable can help diminish the noise

• Subject to loss in cables and connectors

Digital Signal of winds on the coil

• 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 of winds on the coil

• 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 of winds on the coil

• 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 of winds on the coil

• 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 of winds on the coil

• Two main options

• Batteries

• Sea cable

• Power from ship or shore

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

Sea Cables of winds on the coil

• 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 Cables of winds on the coil

• 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