Automation, roboticization or industrial
automation or numerical control is the use of control systems
such as computers to control industrial machinery and processes,
replacing human operators. In the scope of industrialization,
it is a step beyond mechanization. Whereas mechanization
provided human operators with machinery to assist them
with the physical requirements of work, automation greatly
reduces the need for human sensory and mental requirements
as well. Processes and systems can also be automated.
Automation plays an increasingly important role in the
global economy and in daily experience. Engineers strive
to combine automated devices with mathematical and organizational
tools to create complex systems for a rapidly expanding
range of applications and human activities.
There are still many jobs which are in no immediate danger
of automation. No device has been invented which can match
the human eye for accuracy and precision in many tasks;
nor the human ear. Even the admittedly handicapped human
is able to identify and distinguish among far more scents
than any automated device. Human pattern recognition, language
recognition, and language production ability is well beyond
anything currently envisioned by automation engineers.
Specialised hardened computers, referred to as programmable
logic controllers (PLCs), are frequently used to synchronize
the flow of inputs from (physical) sensors and events with
the flow of outputs to actuators and events. This leads
to precisely controlled actions that permit a tight control
of almost any industrial process. (It was these devices
that were feared to be vulnerable to the "Y2K bug",
with such potentially dire consequences, since they are
now so ubiquitous throughout the industrial world.)
Human-machine interfaces (HMI) or computer human interfaces
(CHI), formerly known as man-machine interfaces, are usually
employed to communicate with PLCs and other computers,
such as entering and monitoring temperatures or pressures
for further automated control or emergency response. Service
personnel who monitor and control these interfaces are
often referred to as stationary engineers.
Programmable logic controller
A programmable logic controller (PLC), or programmable
controller is a digital computer used for automation of
industrial processes, such as control of machinery on factory
assembly lines. Unlike general-purpose computers, the PLC
is designed for multiple inputs and output arrangements,
extended temperature ranges, immunity to electrical noise,
and resistance to vibration and impact. Programs to control
machine operation are typically stored in battery-backed
or non-volatile memory. A PLC is an example of a real time
system since output results must be produced in response
to input conditions within a bounded time, otherwise unintended
operation will result.
The main difference from other computers is that PLCs are
armored for severe condition (dust, moisture, heat, cold,
etc) and have the facility for extensive input/output (I/O)
arrangements. These connect the PLC to sensors and actuators.
PLCs read limit switches, analog process variables (such
as temperature and pressure), and the positions of complex
positioning systems. Some even use machine vision. On the
actuator side, PLCs operate electric motors, pneumatic
or hydraulic cylinders, magnetic relays or solenoids, or
analog outputs. The input/output arrangements may be built
into a simple PLC, or the PLC may have external I/O modules
attached to a computer network that plugs into the PLC.
PLCs were invented as replacements for automated systems
that would use hundreds or thousands of relays, cam timers,
and drum sequencers. Often, a single PLC can be programmed
to replace thousands of relays. Programmable controllers
were initially adopted by the automotive manufacturing
industry, where software revision replaced the re-wiring
of hard-wired control panels when production models changed.
Many of the earliest PLCs expressed all decision making
logic in simple ladder logic which appeared similar to
electrical schematic diagrams. The electricians were quite
able to trace out circuit problems with schematic diagrams
using ladder logic. This program notation was chosen to
reduce training demands for the existing technicians. Other
early PLCs used a form of instruction list programming,
based on a stack-based logic solver. The functionality
of the PLC has evolved over the years to include sequential
relay control, motion control, process control, distributed
control systems and networking. The data handling, storage,
processing power and communication capabilities of some
modern PLCs are approximately equivalent to desktop computers.
PLC-like programming combined with remote I/O hardware,
allow a general-purpose desktop computer to overlap some
PLCs in certain applications. Under the IEC 61131-3 standard,
PLCs can be programmed using standards-based programming
languages. A graphical programming notation called Sequential
Function Charts is available on certain programmable controllers.
Programming:
Early PLCs, up to the mid-1980s, were programmed using
proprietary programming panels or special-purpose programming
terminals, which often had dedicated function keys representing
the various logical elements of PLC programs. Programs
were stored on cassette tape cartridges. Facilities for
printing and documentation were very minimal due to lack
of memory capacity. More recently, PLC programs are typically
written in a special application on a personal computer,
then downloaded by a direct-connection cable or over a
network to the PLC. The very oldest PLCs used non-volatile
magnetic core memory but now the program is stored in the
PLC either in battery-backed-up RAM or some other non-volatile
flash memory.
Early PLCs were designed to replace relay logic systems.
These PLCs were programmed in "ladder logic",
which strongly resembles a schematic diagram of relay logic.
Modern PLCs can be programmed in a variety of ways, from
ladder logic to more traditional programming languages
such as BASIC and C. Another method is State Logic, a Very
High Level Programming Language designed to program PLCs
based on State Transition Diagrams.
Recently, the International standard IEC 61131-3 has become
popular. IEC 61131-3 currently defines five programming
languages for programmable control systems: FBD (Function
block diagram), LD (Ladder diagram), ST (Structured text,
similar to the Pascal programming language), IL (Instruction
list, similar to assembly language) and SFC (Sequential
function chart). These techniques emphasize logical organization
of operations.
While the fundamental concepts of PLC programming are common
to all manufacturers, differences in I/O addressing, memory
organization and instruction sets mean that PLC programs
are never perfectly interchangeable between different makers.
Even within the same product line of a single manufacturer,
different models may not be directly compatible.
SCADA:
SCADA is
the abbreviation for Supervisory Control And Data Acquisition.
In Europe and Russia, SCADA refers
to a large-scale, distributed measurement and control
system, while in the rest of the world SCADA may describe
systems
of any size or geographical distribution. SCADA systems
are typically used to perform data collection and control
at the supervisory level. Some systems are called SCADA
despite only performing data acquisition and not control.
The supervisory control system is a system that is placed
on top of a real-time control system to control a process
that is external to the SCADA system (i.e. a computer,
by itself, is not a SCADA system even though it controls
its own power consumption and cooling). This implies
that the system is not critical to control the process
in real
time, as there is a separate or integrated real-time
automated control system that can respond quickly enough
to compensate
for process changes within the time constants of the
process. The process can be industrial, infrastructure
or facility
based as described below:
A) Industrial processes include those of manufacturing,
production, power generation, fabrication, and refining,
and may run in continuous, batch, repetitive, or discrete
modes.
B) Infrastructure processes may be public or private,
and include water treatment and distribution, wastewater
collection and treatment, oil and gas pipelines, electrical
power transmission and distribution, and large communication
systems.
C) Facility processes occur both in public facilities
and private ones, including buildings, airports, ships,
and space stations. They monitor and control HVAC, access,
and energy consumption.
SCADA systems, a branch of instrumentation engineering,
include input-output signal hardware, controllers, human-machine
interfacing ("HMI"), networks, communications,
databases, and software.The term SCADA usually refers to
centralized systems which monitor and control entire sites,
or complexes of systems spread out over large areas (on
the scale of kilometers or miles). Most site control is
performed automatically by remote terminal units ("RTUs")
or by programmable logic controllers ("PLCs").
Host control functions are usually restricted to basic
site overriding or supervisory level intervention. For
example, a PLC may control the flow of cooling water through
part of an industrial process, but the SCADA system may
allow operators to change the set points for the flow,
and enable alarm conditions, such as loss of flow and high
temperature, to be displayed and recorded. The feedback
control loop passes through the RTU or PLC, while the SCADA
system monitors the overall performance of the loop.
Data acquisition begins at the RTU or PLC level and includes
meter readings and equipment status reports that are
communicated to SCADA as required. Data is then compiled
and formatted
in such a way that a control room operator using the
HMI can make supervisory decisions to adjust or override
normal
RTU (PLC) controls. Data may also be fed to a Historian,
often built on a commodity Database Management System,
to allow trending and other analytical auditing.
SCADA systems typically implement a distributed database,
commonly referred to as a tag database, which contains
data elements called tags or points. A point represents
a single input or output value monitored or controlled
by the system. Points can be either "hard" or "soft".
A hard point represents an actual input or output within
the system, while a soft point results from logic and math
operations applied to other points. (Most implementations
conceptually remove the distinction by making every property
a "soft" point expression, which may, in the
simplest case, equal a single hard point.) Points are normally
stored as value-timestamp pairs: a value, and the timestamp
when it was recorded or calculated. A series of value-timestamp
pairs gives the history of that point. It's also common
to store additional metadata with tags, such as the path
to a field device or PLC register, design time comments,
and alarm information.
Complete SCADA systems or Distributed Control Systems
("DCS")
may be acquired from a single supplier, but they are more
often assembled from hardware and software components available
from ABB, Allen-Bradley, DirectLOGIC, GE Fanuc, Omron,
Schneider Electric, Schweitzer Engineering Laboratories,
and Siemens PLCs, along with related HMI packages from
Adroit, Citect, Control Microsystems, GE Fanuc,Honeywell,
ICONICS, Inductive Automation, Kongsberg Maritime, Rockwell
Automation, Schneider Electric, Siemens, Elgama Sistemos,
SUPCON, Telvent, COPS C-DAC open process Solution [C-DAC]
and Wonderware.
Human Machine Interface:
A Human-Machine
Interface or HMI is the apparatus which presents process
data to a
human
operator, and through which the human operator controls
the process. The HMI industry was essentially born
out of a need for a standardized way to monitor and to
control
multiple remote controllers, PLCs and other control
devices. While a PLC does provide automated, pre-programmed
control
over a process, they are usually distributed across
a plant, making it difficult to gather data from them
manually.
Historically PLCs had no standardized way to present
information
to an operator. The SCADA system gathers information
from the PLCs and other controllers via some form of
network,
and combines and formats the information. An HMI may
also be linked to a database, to provide trending,
diagnostic data, and management information such as scheduled
maintenance
procedures, logistic information, detailed schematics
for
a particular sensor or machine, and expert-system troubleshooting
guides. Since about 1998, virtually all major PLC manufacturers
have offered integrated HMI/SCADA systems, many of
them using open and non-proprietary communications protocols.
Numerous specialized third-party HMI/SCADA packages,
offering built-in compatibility with most major PLCs,
have also
entered the market, allowing mechanical engineers,
electrical
engineers and technicians to configure HMIs themselves,
without the need for a custom-made program written
by a software developer. SCADA is popular, due to its
compatibility
and reliability. It is used in small applications,
like controlling the temperature of a room, to large
applications,
such as the control of nuclear power plants.
VLSI:
Very-large-scale
integration (VLSI) is the process of creating integrated
circuits by combining thousands
of transistor-based circuits into a single chip.
VLSI began in the 1970s when complex semiconductor and
communication
technologies were being developed. The microprocessor
is
a VLSI device. The term is no longer as common as
it once was, as chips have increased in complexity into
the hundreds
of millions of transistors.
The first semiconductor chips held one transistor
each. Subsequent advances added more and more transistors,
and as a consequence more individual functions or
systems
were
integrated over time. The first integrated circuits
held only a few devices, perhaps as many as ten diodes,
transistors,
resistors and capacitors, making it possible to fabricate
one or more logic gates on a single device. Now known
retrospectively as "small-scale integration" (SSI), improvements
in technique led to devices with hundreds of logic gates,
known as large-scale integration (LSI), i.e. systems with
at least a thousand logic gates. Current technology has
moved far past this mark and today's microprocessors have
many millions of gates and hundreds of millions of individual
transistors.
As of early 2008, billion-transistor processors are
commercially available, an example of which is Intel's
Montecito Itanium
chip. This is expected to become more commonplace
as semiconductor fabrication moves from the current
generation
of 65 nm
processes to the next 45 nm generations. At one time,
there was an effort to name and calibrate various
levels of large-scale
integration above VLSI. Terms like Ultra-large-scale
Integration (ULSI) were used. But the huge number
of gates and transistors
available on common devices has rendered such fine
distinctions moot. Terms suggesting greater than
VLSI levels of integration
are no longer in widespread use. Even VLSI is now
somewhat quaint, given the common assumption that
all microprocessors
are VLSI or better.
Embedded Systems:
An embedded system is a special-purpose
system in which the computer is completely encapsulated
by the device it controls. Unlike a general-purpose computer,
such as a personal computer, an embedded system performs
pre-defined tasks, usually with very specific requirements.
Since the system is dedicated to a specific task, design
engineers can optimize it, reducing the size and cost
of the product. Embedded systems are often mass-produced,
so the cost savings may be multiplied by millions of
items.
An embedded system is a computer system designed to perform
one or a few dedicated functions. An embedded system
is housed on a single microprocessor board with the programs
stored in ROM. Some embedded systems include an operating
system, but many are so specialized that the entire logic
can be implemented as a single program.
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