- •Textbook Series
- •Contents
- •1 DC Electrics - Basic Principles
- •Introduction
- •Electromotive Force (EMF)
- •Current
- •Resistance
- •Factors Affecting the Resistance
- •Units of Resistance
- •Resistors
- •Power
- •Series and Parallel Circuits
- •Kirchoff’s Laws
- •Annex A
- •2 DC Electrics - Switches
- •Switches
- •Proximity Detectors
- •Time Switches
- •Centrifugal Switches
- •3 DC Electrics - Circuit Protection and Capacitors
- •Electrical Faults
- •Circuit Protection Devices
- •Fuses
- •The Cartridge Fuse
- •Spare Fuses
- •High Rupture Capacity (HRC) Fuses
- •Dummy Fuses
- •Current Limiters
- •Circuit Breakers
- •Reverse Current Circuit Breakers
- •Capacitors
- •Capacitance
- •Capacitor in a DC Circuit
- •Capacitor in an AC Circuit
- •Capacitors in Parallel
- •Capacitors in Series
- •4 DC Electrics - Batteries
- •Batteries
- •Secondary Cells
- •Lead Acid Battery
- •Alkaline Battery (Nickel Cadmium, NiCad)
- •Battery Checks
- •Battery Charging
- •Secondary Batteries Summary
- •5 DC Electrics - Magnetism
- •Magnetism
- •Temporary Magnets
- •Permanent Magnets
- •Permeability
- •Magnetism
- •The Molecular Structure of Magnets
- •The Magnetic Effect of a Current
- •The Corkscrew Rule
- •The Magnetic Field of a Solenoid
- •The Right Hand Grasp Rule
- •The Strength of the Field of a Solenoid
- •Solenoid and Relay
- •The Forces on a Conductor Which is Carrying a Current
- •Questions
- •Answers
- •6 DC Electrics - Generators and Alternators
- •Electromagnetic Induction
- •Fleming’s Right Hand Rule
- •Faraday’s Law
- •Lenz’s Law
- •Simple Generator
- •Simple DC Generator
- •Characteristics of the Series Wound DC Generator
- •Commutator Ripple
- •Characteristics of the Shunt Wound DC Generator
- •A Compound Wound DC Generator
- •Flashing the Generator Field
- •Alternators
- •Voltage Control
- •Voltage Regulator Operation
- •Layout of a Generator System
- •Load Sharing Circuits
- •Operation of Load Sharing Circuit
- •7 DC Electrics - DC Motors
- •Electric Motors
- •Fleming’s Left Hand Rule
- •Practical DC Motor
- •Back EMF
- •Slow Start Resistor
- •Commutation
- •Series Wound Motors
- •Shunt Wound Motors
- •Starter-generator Systems
- •Actuators
- •Solenoid Actuators
- •Motor Actuator Construction
- •The Split Field Series Actuator
- •The Split Field Series Actuator Operation
- •Motor Actuators
- •Rotary Actuators
- •Linear Actuators
- •Actuator Brakes
- •Actuator Clutches
- •Visual Indicators Used with Linear Actuators
- •Visual Indicators Used with Rotary Actuators
- •Indicator Lights
- •Electromagnetic Indicators
- •Questions
- •Answers
- •8 DC Electrics - Aircraft Electrical Power Systems
- •Aircraft Electrical Power Systems
- •Dipole or Two Wire System
- •Single Pole (Unipole or Earth Return) System
- •Generators and Alternators
- •Voltage Regulators
- •Overvoltage Protection Unit
- •Generator Cut-out or Reverse Current Relay
- •Rectifiers
- •Inverters
- •The Generator Differential Cut-out
- •Generator (or Alternator) Warning Light
- •Generator (or Alternator) Master Switch
- •Monitoring Instruments
- •Ammeters and Voltmeters
- •The Battery
- •Bus Bars
- •Bus Bar Systems
- •Parallel Bus Bar System
- •Load Shedding
- •Generator or Alternator Failure
- •9 DC Electrics - Bonding and Screening
- •Bonding
- •The Static Discharge System or Static Wicks
- •Discharge of Static on Touchdown
- •Screening
- •Questions
- •Answers
- •10 DC Electrics - Specimen Questions
- •Questions – General 1
- •Questions – General 2
- •Answers – General 1
- •Answers – General 2
- •11 AC Electrics - Introduction to AC
- •Introduction
- •The Nature of Alternating Current
- •Terms
- •The Relationship of Current and Voltage in an AC Circuit
- •Resistance in AC Circuits
- •Inductance in AC Circuits
- •Inductive Reactance
- •Capacitance in AC Circuits
- •Capacitive Reactance
- •Impedance
- •Resonant Circuits
- •Summary
- •Power in AC Circuits
- •Power in a Purely Resistive Circuit
- •Power in a Purely Inductive Circuit
- •Power in a Capacitive Circuit
- •Power in a Practical AC Circuit
- •Power Factor
- •Power Factor Resume
- •Questions
- •Answers
- •12 AC Electrics - Alternators
- •Introduction to Aircraft Power Supplies
- •Generators / Alternators
- •Rotating Armature Alternator
- •Rotating Field Alternator
- •Alternator Output Rating
- •A Single Phase Alternator
- •Polyphase Circuits
- •Three Phase Alternator Connections
- •The Four Wire Star Connection
- •Delta Connected Alternator
- •Practical AC Generators
- •Brushed Alternators
- •Brushless Alternators
- •Frequency Wild Alternators
- •Obtaining a Constant Frequency Supply from a Frequency Wild System
- •Constant Frequency Alternators
- •Constant Speed Generator Drive Systems
- •CSDU Fault Indications in the Cockpit
- •The Drive Disconnect Unit (Dog Clutch Disconnect)
- •Variable Speed Constant Frequency Power Systems (VSCF)
- •Self-excited Generators
- •Load Sharing or Paralleling of Constant Frequency Alternators
- •Real Load
- •Reactive Load
- •Parallel Connection
- •Before Connecting in Parallel
- •Layout of a Paralleled System
- •Real Load Sharing
- •Reactive Load Sharing
- •Load Sharing General
- •Alternator Cooling
- •Generator Fault Protection
- •Bus Tie Breakers (BTBs)
- •Discriminatory Circuits
- •Differential Fault Protection
- •Synchronizing Units
- •Generator Failure Warning Light
- •Load Meters
- •Voltage and Frequency Meters
- •Generator Control Unit (GCU)
- •Emergency Supplies
- •The Ram Air Turbine (RAT)
- •The Auxiliary Power Unit (APU)
- •The Static Inverter
- •Ground Power Constant Frequency Supply System
- •Typical Controls and Indications
- •Questions
- •Answers
- •13 AC Electrics - Practical Aircraft Systems
- •Power Distribution
- •The Split Bus System
- •Parallel Bus Bar System
- •Questions
- •Answers
- •14 AC Electrics - Transformers
- •Transformers
- •Transformation Ratio
- •Power in a Transformer
- •Three Phase Transformers
- •Autotransformers
- •Rectification of Alternating Current
- •Half Wave Rectification
- •Full Wave Rectification
- •Three Phase Rectifiers
- •Transformer Rectifier Units (TRUs)
- •Inverters
- •Questions
- •Answers
- •15 AC Electrics - AC Motors
- •Alternating Current Motors
- •The Principle of Operation of AC Motors
- •The Synchronous Motor
- •The Induction Motor
- •The Squirrel Cage Rotor
- •The Induction Motor Stator
- •Slip Speed
- •Starting Single Phase Induction Motors
- •Fault Operation
- •Questions
- •Answers
- •16 AC Electrics - Semiconductors
- •An Introduction to Semiconductors
- •Conductors and Insulators
- •Semiconductors
- •N-Type Material
- •P-Type Material
- •Current Flow
- •The P-N Junction
- •Reverse Bias
- •Forward Bias
- •The Junction Diode
- •The Bipolar or Junction Transistor
- •Summary
- •17 AC Electrics - Logic Gates
- •An Introduction to Logic Gates
- •Binary Logic
- •Truth Tables
- •Gate Symbols
- •Positive and Negative Logic
- •The ‘AND’ Gate
- •The ‘OR’ Gate
- •The ‘INVERT’ or ‘NOT’ Gate
- •The ‘NAND’ Gate
- •The ‘NOR’ Gate
- •The ‘EXCLUSIVE OR’ Gate
- •Questions
- •Answers
- •18 Index
Chapter
17
AC Electrics - Logic Gates
An Introduction to Logic Gates . . . . . . . . . . . . |
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Binary Logic . . . . . . . . . . . . . . . . . . . . |
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Truth Tables . . . . . . . . . . . . . . . . . . . . |
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Gate Symbols . . . . . . . . . . . . . . . . . . . |
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Positive and Negative Logic . . . . . . . . . . . . . . |
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The ‘AND’ Gate . . . . . . . . . . . . . . . . . . |
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The ‘OR’ Gate . . . . . . . . . . . . . . . . . . . |
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The ‘INVERT’ or ‘NOT’ Gate . . . . . . . . . . . . . . |
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The ‘NAND’ Gate . . . . . . . . . . . . . . . . . . |
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The ‘NOR’ Gate . . . . . . . . . . . . . . . . . . |
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The ‘EXCLUSIVE OR’ Gate . . . . . . . . . . . . . . |
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Questions . . . . . . . . . . . . . . . . . . . . |
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17 AC Electrics -Logic Gates
Gates Logic - Electrics AC 17
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AC Electrics - Logic Gates 17
An Introduction to Logic Gates
Logic gates, or gates, are a type of fundamental function performed by computers and related equipment. A single integrated circuit (IC) within a computer contains several gate circuits. Each gate may have several inputs and must have only one output.
There are six commonly used logic gates: the ‘AND’, the ‘OR’, the ‘INVERT’, the ‘NOR’, the ‘NAND’ and the ‘EXCLUSIVE OR’. The name of each gate represents the function it performs.
Binary Logic
Logic gates are of a binary nature, i.e. the inputs and the outputs are in one of two states expressed by the digital notation ‘1’ or ‘0’. Other corresponding expressions are also frequently used, they are:
•‘1’ - on; true; high (H); closed; engaged
•‘0’ - off; false; low (L); open; disengaged
Truth Tables
Truth Tables are a systematic means of displaying binary data. Truth tables illustrate the relationship between a logic gate’s inputs and outputs. This type of data display can be used to describe the operation of a gate. For troubleshooting purposes, the truth table data is often reviewed in order to determine the correct output signal for a given set of inputs.
Gate Symbols
Each logic gate has a symbol of a specific shape. The symbols are designated to “point” in a given direction, that is, the inputs are always listed on the left of the symbol and the outputs on the right.
Since logic gates operate using digital data, all input and output signals will be made up of ‘1’s or ‘0’s. Typically the symbol ‘1’ represents ‘ON’ or voltage positive, and the symbol ‘0’ represents ‘OFF’, or voltage negative. Voltage negative is often referred to as zero voltage or the circuit’s ground.
Positive and Negative Logic
As stated earlier, logic circuit input and output signals consist of two distinct levels. These levels are often referred to as ‘binary 1’ and ‘binary 0’. The actual voltage levels required to achieve a ‘binary 1’ or ‘binary 0’ may vary between circuits.
•If positive logic is used in the digital circuit, a ‘binary 1’ equals a high voltage level and a ‘binary 0’ equals a low voltage level. The actual voltage values may be either both positive or both negative, or one positive and one negative. The only stipulation for positive logic is that a ‘binary 1’ is created by a greater positive voltage than a ‘binary 0’ . Each signal represents the greater positive voltage value as a ‘binary 1’, and therefore the following examples employ the positive logic concept. Most digital systems employ positive logic throughout the entire computer and related component circuitry.
AC Electrics - Logic Gates 17
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17 AC Electrics -Logic Gates
•The negative logic concept defines ‘binary 1’ as the lower voltage value and ‘binary 0’ as the higher voltage value (more positive). Although less popular, negative logic is used in some systems in order to meet certain design parameters.
The ‘AND’ Gate
The ‘AND’ gate is used to represent a situation where all inputs to the gate must be ‘1’ (on) to produce a ‘1’ (on) output. To be an ‘AND’ gate, input No. 1 and input No. 2 and input No. 3 etc, must be ‘1’ to produce a ‘1’ output. If any input is a ‘0’ (off), the output will be ‘0’ (off). The symbol and the truth table for a two-input AND gate are illustrated in Figure 17.1.
Gates Logic - Electrics AC 17
Figure 17.1 The symbol and truth table for an ‘AND’ gate
A simple ‘AND’ circuit may also be represented by two switches in series used to turn on a light as shown in Figure 17.1. If both switches (inputs) are ‘1’ (on), the light will turn ‘1’ (on). If either switch is ‘0’ (off), the light will be ‘0’ (off).
The ‘AND’ gate is sometimes called an ‘ALL or NOTHING’ gate.
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