Lecture #2 Basic Electricity

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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

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
• Many similarities with the flow of water
• Water flows

because of a

pressure

difference

• Bigger pipes

allow more

flow

A complete circuit is required for current to flow

• Also required:
• A source of “pressure” (voltage)
• Optional:
• Switch
• Something to do work
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)
• Resistance: the resistance to flow
• Friction in the pipe
• Units
• Ω – Ohm
• Symbol
• -WW-
Simple Equations
• Ohm\'s Law

E=IR

• E– Voltage (volts)
• I – Current (amps)
• R – Resistance (ohm)
• Power

P=IE

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

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
• Variable resistor: 2 terminals
• Examples
• Audio control
• Joysitck
• Rheostat
• Potentiometer: 3 terminals
• Voltage divider
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
Diodes
• Used to separate battery packs
• Also used to “idiot proof” connections
• Called “diode isolation”
• More later….
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
• 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……
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
• C1+C2+C3...=Ctotal
• Opposite that of Resistors

Using capacitors:

• Absorb voltage spikes
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
• 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 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

DC vs AC

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
• 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.
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
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
• 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
• 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
• Cars
• Horn
• Lights
• Starter
• Ocean:
• Sensor power
• Burn wires
• Controller power
• motors
Transistors
• 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)
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• Two main options
• Batteries
• Sea cable
• Power from ship or shore
• Usually allows data to be “Live Feed” as well
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 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