PowerPoint ® Presentation Chapter 7 PLC and System Interfacing Systems Primary Systems System Interfacing Electrical Circuits Basic Electrical Circuits.

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.


Electrical systems use alternating current (AC) or direct current (DC) to produce power.


Electronic systems monitor and control electricity to send and/or receive information, produce sound or vision, store data, control circuits, or perform other work.


Fluid power systems produce work by transmitting fluid under pressure through pipework.


Mechanical systems transmit power using gears, belts, chains, shafts, couplings, and linkages.


Informational systems display electrical, electronic, fluid power, and mechanical quantities and conditions to indicate the status of a circuit, process, or application.


Interfacing systems interconnect primary systems of various types.


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.


System interfacing permits devices and components of various levels of voltage, current, and power to work together as a system.


Circuit conditioning is required any time the existing electrical power is not at the proper phase, voltage, or current level for the application.


Interface devices are required any time an input device or output component is not directly compatible with a PLC.


Interface devices change or condition a system in a variety of ways.


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.


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.


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.


PLCs and PCs are interconnected through communication lines to form various types and levels of networks.


Sensors and switches are typical input devices to a PLC, with lighting, motors and information displays being typical output components for a PLC.


Relays, contactors, and motor starters are the most common interface devices used to control high-power loads.


Electromechanical relays have sets of contacts that are closed by magnetic force.


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.


The type of relay used depends on the life expectancy, electrical requirements, and cost requirements of the application.


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.


The output side of a solid-state relay can be used to control high-voltage medium-power loads such as 3 heating elements.


Contactors are designed to control high-power, non-motor loads.


Contactors allow PLC output circuitry to be rated much lower than the loads that the PLC is controlling.


Magnetic motor starters use a small control current to energize a coil to send high power to a motor.


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.


Electric motor drives control motor speed by controlling the frequency of the electricity to a motor.


Any type of switch contacts (pushbutton, pressure switch, PLC output contacts) can be used to control an electric motor drive.

PowerPoint ® Presentation Chapter 7 PLC and System Interfacing Systems Primary Systems System Interfacing Electrical Circuits Basic Electrical Circuits.

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