A PLC or programmable controller is a computer based solid state device that controls industrial equipment and processes.
Initially designed to perform the logic functions executed by relays, drum switches and mechanical timer/counters, it has
been extended to analog control as well.
A typical PLC system consists of a processor and an input/output system all mounted in a rack like system. The PLC system
is a cost effective solution for applications with a high ratio of digital to analog points in a system.
Integrated manufacturing uses computers to connect physically separated processes. When
integrated, the processes can share information and initiate actions. This allows decisions to be
made faster and with fewer errors.
Despite the great technological advancement experienced in recent years,
Programmable Logic Controllers (PLC) are still used in many applications from the real
world and still play a central role in infrastructure of industrial automation. PLC operate in
the factory-floor level and are responsible typically for implementing logical control,
regulatory control strategies, such as PID and fuzzy-based algorithms, and safety logics.
Usually PLC are interconnected with the supervision level through communication
network, such as Ethernet networks, in order to work in an integrated form....
Programmable Logic Controllers (PLCs), also referred to as
programmable controllers, are in the computer family. They are
used in commercial and industrial applications. A PLC monitors
inputs, makes decisions based on its program, and controls
outputs to automate a process or machine.
This practical book gives a comprehensive introduction to the concepts and languages of the new standard IEC 61131 used to program industrial control systems. A summary of the special requirements in programming industrial automation systems and the corresponding features in the IEC 61131-3 standard makes it suitable for students as well as PLC experts. The material is presented in an easy-to-understand form using numerous examples, illustrations and summary tables. There is also a purchaser's guide and a CD-ROM containing two reduced but functional versions of programming systems.
Control engineering has evolved over time. In the past humans were the main
method for controlling a system. More recently electricity has been used for control and
early electrical control was based on relays. These relays allow power to be switched on
and off without a mechanical switch. It is common to use relays to make simple logical
control decisions. The development of low cost computer has brought the most recent revolution,
the Programmable Logic Controller (PLC). The advent of the PLC began in the
1970s, and has become the most common choice for manufacturing controls....
In ladder logic there are multiple types of outputs, but these are not consistently available on all PLCs. Some of the outputs will be externally connected to devices outside the PLC, but it is also possible to use internal memory locations in the PLC. Six types of outputs are shown in Figure 2.12. The first is a normal output, when energized the output will turn on, and energize an output. The circle with a diagonal line through is a normally on output. When energized the output will turn off. This type of output is not available on all PLC types....
Ladder Logic Outputs
In ladder logic there are multiple types of outputs, but these are not consistently available on all PLCs. Some of the outputs will be externally connected to devices outside the PLC, but it is also possible to use internal memory locations in the PLC. Six types of outputs are shown in Figure 2.12. The first is a normal output, when energized the output will turn on, and energize an output. The circle with a diagonal line through is a normally on output. When energized the output will turn off. This type of output is not available on all...
A PLC (i.e. Programmable Logic Controller) is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs. The user enters a program, usually via software, that gives the desired results.
PLCs are used in many "real world" applications. If there is industry present, chances are good that there is a plc present.
.Click to edit Master title style Instructor
Truong Dinh Chau, Ph.D Department of Automation & Control, Automation Design Center, 109 B3 Ho Chi Minh City Univ. of Tech. Cell phone: +84 (0)91-543-74-40 Email: firstname.lastname@example.org Truong-Dinh.Chau@schneider-electric.com
The function blocks of IEC 61499 resp. the automation objects (functions) of PROFInet are the
“atomic” elements, i.e. the not more divisible base elements, which are used for the engineering view
and as the run time objects. They consists in a body containing the executable algorithms and they
have interconnectable external interfaces for input and output data. Furthermore the function blocks
resp. the automation objects obtain a new kind of interface which is not existing for the function blocks
of the PLC standard IEC 61131-3....