Download - Electronic systems and control 2012
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ELECTRONIC SYSTEMS AND CONTROL
LIEZEL OOSTHUIZEN200932201
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CURRENT
Current is the continuous movement of free electrons through the conductors of a circuit.
Ammeter - Measures the flow of electrons in a circuit, which is known as current - connected in series.
Symbol of current (I). The (I) unit of measurement
of electric current, the ampere, is named after André-Marie Ampère.
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VOLTAGE+ The ability of a cell to
produce current is called voltage.
+ Voltage is the electricalpotential energy.
+ Is measured in Volts.+ Voltmeter Measures the voltage
produced by a power supply – always connected in parallel.
+ Symbol for Volt (V) or (E).
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OHM’S LAW & RESISTANCE
Resistance - Free electrons move through conductors with some degree of friction.
Resistance is measured in Ohm (Ω).
Symbol of resistance (R).
A Resistor - Slows down the flow of electrons in a circuit.
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EQUATIONS Resistance = voltage/current R= V/I Voltage = current x resistance V= I x R Current = voltage/resistance I=V/R
Resistance in Serie: When resistors are connected in Series, the effect is to add more
resistance to the circuit. E.g. The value of resistors in series: RT(Total) =
R1+R2+R3[Resistor Values] *A resistor is a series circuit is called a voltage divider.
Resistance in Parallel: When resistors are connected in parallel, the effect is to reduce the
resistance in the circuit. E.g. The value of resistors in parallel: 1/Rt = 1/R1 + 1/R2 + 1/R3
*Resistors in a parallel circuit is called a current divider.
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CURRENT
VOLTAGE
RESISTANCE
V=
R=I=
Measuredin Volts (V).
Measured in Ohms(Ω).
Measured in Amps (A).
V
AΩ
I = V ÷ R
V = I x R
R = V ÷ I
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RESISTOR COLOUR CODESThe First three bands give the value of the resistor in ohm(Ω).
The fourth band indicates how accurate the given value is.Resistor value: 2% - RED
5% - GOLD 10% - SILVER
E.g.:
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RESISTIVE COMPONENTS
Variable Resistor Can be used to adjust
the flow of current in a circuit.
Thermistor Is a component whose
resistance varies with temperature.
Light Dependent resistor (LDR)
It’s a component whose resistance depends upon the amount of light falling on it – it reacts to light.
When the LDR in the circuit is covered up, the bulb gets dimmer and finally goes out.
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CONTROL ELECTRICS
The switch It’s the simplest
control unit form in an electrical circuit. The simplest type of switch is the single pole single throw switch (SPST).
It has 2 parts: a pole & a contact.
Single pole double throw switch (SPDT).
Double Pole single throw switch (DPST).
Double pole single throw switch(DPDT).
Push to Make & Push to break switches:
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MORE COMMON TYPE OF SWITCHES:
Toggle switch Push Switch
Slide switch Reed Switch
A Rotary Switch
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RELAYS The Relay - is a switch turned on and off by an
electromagnet.
Relay Latch - Fixes a circuit in “On” position. - A latch is like a lock.
Relay Buzzer -The relay switches “on” and “off” very rapidly, producing a buzzing sound.
-A relay can therefore be used to make a crude buzzer.
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CONTROL ELECTRONICS
THE DIODELIGHT EMITTING DIODES (LED)
Is a semiconductor device. It’s a component which allows
current to flow in one direction only. A Semiconductor diode consists of
a PN junction and has two terminals: [P] - Anode(+) [N] – Cathode(-) Current flows from the anode to the
cathode within the diode. When a forward voltage is applied,
the diode conducts. When a reverse voltage is applied,
their is no conduction.
A LED is a special form of diode that gives out light when connected the correct way around.
LED’s normally need to be connected in series with a resistor to prevent them drawing too much current and burning out.
LED’s are used mainly as visual indicators that a circuit is working or an appliance is “On”.
An LED converts electrical energy to light.
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TRANSISTORS
A Transistor is a semiconductor device. Made of three layers of N-Type & P-Type semiconductor material, Geranium
and Silicone. The three layers are called - Emitter, Base & Collector.
There are three types of transistors:
NPN PNP
The NPN Transistor has a small current flowing to the base of the
transistor enables a large current to flow between the collector and emitter. The PNP Transistor uses a small base current and negative base voltage
to control a much larger emitter-collector current. The FET transistor – Field Effect Transistor only needs a small field of
current.
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TIMING CIRCUITS CAPACITORS - A CAPACITOR IS A COMPONENT WHICH CAN STORE AND RELEASE ELECTRICAL ENERGY.
- CAPACITANCE IS MEASURED IN FARAD.
1. POLARIZED - CAPACITOR 2. NON – POLARIZED CAPACITOR
Polarized capacitors tend to be higher value types.
These have a positive(+) and negative(-) lead which must be connected the correct way round in a circuit (+ to + and - to -) .
Non-polarized capacitors which are low value types.
These can be connected either way round in a circuit.
Do not have a (+) or (-) lead.
Normally used to smooth a current in a circuit.
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THREE FACTORS THAT INFLUENCE THE CAPACITY OF A CAPACITOR:
1.) Lowering the surface area of plates.
2.) Increase distance between plates.
3.)The kind of material used for dielectric.
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REFERENCES:
Download.pptx. (n.d.). Retrieved from http://www.tes.co.uk/Download.aspx?storycode=6071059&type=X&id=6269844
explaining how Resistors work.ppt. (n.d.). Retrieved from http://teachersunderground.co.uk/Electronics/explaining%20how%20Resistors%20work.ppt
Garratt,J. (1996). Design and Technology. Cape Town: Cambridge University Press.
Ohm’s Law - Resources - TES. (n.d.). Retrieved April 30, 2012, from http://www.tes.co.uk/teaching-resource/Ohm-s-Law-6071059/addtofavourite/addtofavourite/
Resistor colour code wheel.ppt. (n.d.). Retrieved from http://teachersunderground.co.uk/Electronics/Resistor%20colour%20code%20wheel.ppt