Post on 30-Mar-2015
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PowerPoint® Presentation
Chapter 7PLC and System Interfacing
Chapter 7PLC and System Interfacing
Systems • Primary Systems • System Interfacing • Electrical Circuits • Basic Electrical Circuits • Improving Basic Electrical Circuits • Complex
Electrical Circuits • Interfacing Circuits • Interface Devices • Electromechanical Relays • Solid-State
Relays • Contactor Interfaces • Motor Starter Interfaces • Electric Motor Drive Interfacing
Chapter 7 — PLC and System Interfacing
Primary systems transmit and control the movement of energy.
Chapter 7 — PLC and System Interfacing
Electrical systems use alternating current (AC) or direct current (DC) to produce power.
Chapter 7 — PLC and System Interfacing
Electronic systems monitor and control electricity to send and/or receive information, produce sound or vision, store data, control circuits, or perform other work.
Chapter 7 — PLC and System Interfacing
Fluid power systems produce work by transmitting fluid under pressure through pipework.
Chapter 7 — PLC and System Interfacing
Mechanical systems transmit power using gears, belts, chains, shafts, couplings, and linkages.
Chapter 7 — PLC and System Interfacing
Informational systems display electrical, electronic, fluid power, and mechanical quantities and conditions to indicate the status of a circuit, process, or application.
Chapter 7 — PLC and System Interfacing
Interfacing systems interconnect primary systems of various types.
Chapter 7 — PLC and System Interfacing
Combination systems such as industrial robots interconnect two or more primary systems (hydraulic, pneumatic, mechanical, electrical, electronic, digital, and welding), combining the individual advantages of each system to meet the requirements of a given application.
Chapter 7 — PLC and System Interfacing
System interfacing permits devices and components of various levels of voltage, current, and power to work together as a system.
Chapter 7 — PLC and System Interfacing
Circuit conditioning is required any time the existing electrical power is not at the proper phase, voltage, or current level for the application.
Chapter 7 — PLC and System Interfacing
Interface devices are required any time an input device or output component is not directly compatible with a PLC.
Chapter 7 — PLC and System Interfacing
Interface devices change or condition a system in a variety of ways.
Chapter 7 — PLC and System Interfacing
Basic electrical circuits must include a source of electricity, a method of controlling the flow of electricity, and a component that converts electrical energy into some other usable form of energy. A circuit must also include protection device(s) to ensure that the circuit operates safely and within designed electrical limits.
Chapter 7 — PLC and System Interfacing
Basic PLC-controlled circuits with multiple loads wired in parallel have the loads wired separately to the PLC output terminals and the output terminals programmed to be parallel.
Chapter 7 — PLC and System Interfacing
Basic circuits are improved by adding additional protection, instrumentation for monitoring circuit parameters, and finer controls, and by interconnecting all basic circuits into a system.
Chapter 7 — PLC and System Interfacing
PLCs and PCs are interconnected through communication lines to form various types and levels of networks.
Chapter 7 — PLC and System Interfacing
Sensors and switches are typical input devices to a PLC, with lighting, motors and information displays being typical output components for a PLC.
Chapter 7 — PLC and System Interfacing
Relays, contactors, and motor starters are the most common interface devices used to control high-power loads.
Chapter 7 — PLC and System Interfacing
Electromechanical relays have sets of contacts that are closed by magnetic force.
Chapter 7 — PLC and System Interfacing
Solid-state relays have an input voltage range, such as 3 VDC to 32 VDC, that allows a single solid-state relay to be used with most electronic circuits and PLC output modules.
Chapter 7 — PLC and System Interfacing
The type of relay used depends on the life expectancy, electrical requirements, and cost requirements of the application.
Chapter 7 — PLC and System Interfacing
Any load that can cause a problem to the output section or module of a PLC must include an interface device between the PLC and the load.
Chapter 7 — PLC and System Interfacing
The output side of a solid-state relay can be used to control high-voltage medium-power loads such as 3 heating elements.
Chapter 7 — PLC and System Interfacing
Contactors are designed to control high-power, non-motor loads.
Chapter 7 — PLC and System Interfacing
Contactors allow PLC output circuitry to be rated much lower than the loads that the PLC is controlling.
Chapter 7 — PLC and System Interfacing
Magnetic motor starters use a small control current to energize a coil to send high power to a motor.
Chapter 7 — PLC and System Interfacing
When the coil of a motor starter and the control circuit require lower voltage, a step-down transformer is used to reduce the high voltage to a low voltage.
Chapter 7 — PLC and System Interfacing
Electric motor drives control motor speed by controlling the frequency of the electricity to a motor.
Chapter 7 — PLC and System Interfacing
Any type of switch contacts (pushbutton, pressure switch, PLC output contacts) can be used to control an electric motor drive.