BY:

SAYED QAISAR SHAH

BS TELECOM,CCNA,CWNA
REG# A1DE-109004
DATE: 01-08-12
DCS (Distributed Control System)
INTRODUCTION

 Digital Control Systems(DCS) also known as Distributed Control System is

the brain of the control system.
 It is generally, since the 1970s, digital, and normally consists of field
instruments, connected via wiring to computer buses or electrical buses to
multiplexer/de multiplexers and A/D's or analog to digital and finally the
Human-Machine Interface (HMI) or control consoles. A DCS is a process
control system that uses a network to interconnect sensors, controllers,
operator terminals and actuators. A DCS typically contains one or more
computers for control and mostly use both proprietary interconnections and
protocols for communications.
 Control Systems are collectively named as "ICSS" Integrated Control and Safety
System. Distinctly identified as "BPCS" Basic Process Control System. "SIS"
Safety Instrumentation System. "F&G" Fire and Gas System.
 DCS is employed in BPCS as well as used and prevalent control system.
DCS (Cont..)
 The DCS is a control system which collects the data from
the field and decides what to do with them. Data from the
field can either be stored for future reference, used for
simple process control, use in conjunction with data from
another part of the plant for advanced control strategies.
 A distributed control system (DCS) is part of a
manufacturing system.
 Distributed control systems (DCS) are used in industrial
and civil engineering applications to monitor and control
distributed equipment with remote human intervention.
What must be in the DCS for it to
be able to do so much?
 Operator Console
These are like the monitors of our computers. They provide us with the
feedback of what they are doing in the plant as well as the command we issue
to the control system. These are also the places where operators issue
commands to the field instruments.

 Engineering Station
These are stations for engineers to configure the system and also to implement
control algorithms.

 History Module
This is like the hard disk of our PCs. They store the configurations of the DCS
as well as the configurations of all the points in the plant. They also store the
graphic files that are shown in the console and in most systems these days they
are able to store some plant operating data.
Cont..
 Data Historian
These are usually extra pieces of software that are dedicated to store process
variables, set points and output values. They are usually of higher scanning
rates than that available in the history module.
Control Modules
These are like the brains of the DCS. Specially customized blocks are found
here. These are customized to do control functions like PID control, ratio
control, simple arithmetic and dynamic compensation. These days, advanced
control features can also be found in them.
I/O
These manage the input and output of the DCS. Input and output can be
digital or analogues. Digital I/Os are those like on/off, start/stop signals. Most
of the process measurements and controller outputs are considered
analogue. These are the points where the field instruments are hard-wired to.
 All above mentioned elements are connected by using a network, nowadays
very often used is Ethernet.
How does a DCS work?
 In the field you have sensors and gauges that give and
receive information. They convert this information into a
electric signal that is sent to a control room somewhere in
the field. This control room has programmed logic that is
able to converts the signal into a pressure, flow rate,
concentration, temperature, or level. This logic also
contains the information that controls the process and
takes the signal compares it with the set point sent from
the operator may or may not be in the field and sends a
signal to the manipulated variables in the field. The DCS
covers all of the computer logic from the operator screen to
the field box that contain the logic.
Shutdown systems
 Shutdown system are the emergency setting of the
logic to make sure the process can be contained and is
environmentally safe. These setting are important for
emergency response of the system. It is the job of the
DCS to contain the logic for the shutdown system and
be able to operate when a process exceed a certain
limit.
DCS APPLICATIONS
 DCS is a very broad term that describes solutions
across a large variety of industries, including:

* Electrical power grids and electrical generation

plants
* Environmental control systems
* Traffic signals
* Water management systems
* Refining and chemical plants
* Pharmaceutical manufacturing.
Distributed Control System
SCADA (Supervisory Control And Data
Acquisition)
INTRODUCTION
 As the name indicates, it is not a full control system, but rather focuses
on the supervisory level. As such, it is a purely software package that is
positioned on top of hardware to which it is interfaced, in general via
Programmable Logic Controllers (PLC's), or other commercial
hardware modules.
 In reality, the primary purpose of SCADA is to monitor, control and
alarm plant or regional operating systems from a central location.
While override control is possible, it is infrequently utilized; however
control set points are quite regularly changed by SCADA.
 SCADA systems have made substantial progress over the recent years in
terms of functionality, scalability, performance and openness such that
they are an alternative to in house development even for very
demanding and complex control systems.
Cont..
A SCADA application has two elements:
 The process/system/machinery you want to monitor a
control - this can be a power plant, a water system, a
network, a system of traffic lights, or anything else.
 A network of intelligent devices that interfaces with the
first system through sensors and control outputs. This
network, which is the SCADA system, gives you the ability
to measure and control specific elements of the first
system.
 You can build a SCADA system using several different kinds
of technologies and protocols. This white paper will help
you evaluate your options and decide what kind
of SCADA system is best for your needs.
Where is SCADA Used?
 You can use SCADA to manage any kind of equipment. Typically,
SCADA systems are used to automate complex industrial processes
where human control is impractical - systems where there are more
control factors, and more fast-moving control factors, than human
beings can comfortably manage.
 Around the world, SCADA systems control:
 • Electric power generation, transmission and
distribution: Electric utilities use SCADA systems to detect current
flow and line voltage, to monitor the operation of circuit breakers, and
to take sections of the power grid online or offline.
 • Water and sewage: State and municipal water utilities use SCADA to
monitor and regulate water flow, reservoir levels, pipe pressure and
other factors.
 • Buildings, facilities and environments: Facility managers use
SCADA to control HVAC, refrigeration units, lighting and entry
systems.
Cont..
 • Manufacturing: SCADA systems manage parts inventories for just-in-time
manufacturing, regulate industrial automation and robots, and monitor
process and quality control.
 • Mass transit: Transit authorities use SCADA to regulate electricity to
subways, trams and trolley buses; to automate traffic signals for rail systems; to
track and locate trains and buses; and to control railroad crossing gates.
 • Traffic signals: SCADA regulates traffic lights, controls traffic flow and
detects out-of-order signals.

 As I'm sure you can imagine, this very short list barely hints at all the potential
applications for SCADA systems. SCADA is used in nearly every industry and
public infrastructure project - anywhere where automation increases efficiency.
 What's more, these examples don't show how deep and complex SCADA data
can be. In every industry, managers need to control multiple factors and the
interactions between those factors. SCADA systems provide the sensing
capabilities and the computational power to track everything that's relevant to
your operations.
Cont..
 SCADA systems are used not only in industrial processes:
e.g. steel making, power generation (conventional and
nuclear) and distribution, chemistry, but also in some
experimental facilities such as nuclear fusion. The size of
such plants range from a few 1000 to several 10 thousands
input/output (I/O) channels. However, SCADA systems
evolve rapidly and are now penetrating the market of
plants with a number of I/O channels of several 100
thousands I/O's.

 SCADA systems used to run on DOS, VMS and UNIX; in

recent years all SCADA vendors have moved to NT,
Windows XP, Windows Server 2003 and some also to
Linux.
Hardware Architecture
Cont…
Hardware Architecture
One distinguishes two basic layers in a SCADA system: the
"client layer" which caters for the man machine interaction
and the "data server layer" which handles most of the
process data control activities. The data servers
communicate with devices in the field through process
controllers. Process controllers, e.g. PLC's, are connected to
the data servers either directly or via networks or field
buses that are proprietary (e.g. Siemens H1), or non-
proprietary (e.g. Profibus). Data servers are connected to
each other and to client stations via an Ethernet LAN.
Software Architecture
Cont…
 The products are multi-tasking and are based upon a
real-time database (RTDB) located in one or more
servers. Servers are responsible for data acquisition
and handling (e.g. polling controllers, alarm checking,
calculations, logging and archiving) on a set of
parameters, typically those they are connected to.
 However, it is possible to have dedicated servers for
particular tasks, e.g. historian, data logger, alarm
handler. The figure above shows a generic SCADA
software architecture.
How SCADA Systems Work?
A SCADA system performs four functions:
 Data acquisition
 Networked data communication
 Data presentation
 Control
These functions are performed by four kinds of SCADA components:
 Sensors (either digital or analog) and control relays that directly
interface with the managed system.
 Remote telemetry units (RTUs). These are small computerized units
deployed in the field at specific sites and locations. RTUs (Remote
Telemetry Units) serve as local collection points for gathering reports
from sensors and delivering commands to control relays.
Cont…
 SCADA master units. These are larger computer
consoles that serve as the central processor for the
SCADA system. Master units provide a human
interface to the system and automatically regulate the
managed system in response to sensor inputs.
 The communications network that connects the
SCADA master unit to the RTUs in the field.
The World's Simplest SCADA
System
Cont…
 The simplest possible SCADA system would be a single
circuit that notifies you of one event. Imagine a
fabrication machine that produces widgets. Every time
the machine finishes a widget, it activates a switch.
The switch turns on a light on a panel, which tells a
human operator that a widget has been completed.
 Obviously, a real SCADA system does more than this
simple model. But the principle is the same. A full-
scale SCADA system just monitors more stuff over
greater distances.
Data Acquisition
 First, the systems you need to monitor are much more complex than just one
machine with one output. So a real-life SCADA system needs to monitor
hundreds or thousands of sensors. Some sensors measure inputs into the
system (for example, water flowing into a reservoir), and some sensors measure
outputs (like valve pressure as water is released from the reservoir).
Some of those sensors measure simple events that can be detected by a
straightforward on/off switch, called a discrete input (or digital input). For
example, in our simple model of the widget fabricator, the switch that turns on
the light would be a discrete input. In real life, discrete inputs are used to
measure simple states, like whether equipment is on or off, or tripwire alarms,
like a power failure at a critical facility.
 Some sensors measure more complex situations where exact measurement is
important. These are analog sensors, which can detect continuous changes in a
voltage or current input. Analog sensors are used to track fluid levels in tanks,
voltage levels in batteries, temperature and other factors that can be measured
in a continuous range of input..
Cont…
 For most analog factors, there is a normal range
defined by a bottom and top level. For example, you
may want the temperature in a server room to stay
between 60 and 85 degrees Fahrenheit. If the
temperature goes above or below this range, it will
trigger a threshold alarm. In more advanced systems,
there are four threshold alarms for analog sensors,
defining Major Under, Minor Under, Minor Over and
Major Over alarms.
Data Communication
 In our simple model of the widget fabricator, the "network" is
just the wire leading from the switch to the panel light. In real
life, you want to be able to monitor multiple systems from a
central location, so you need a communications network to
transport all the data collected from your sensors.
 Early SCADA networks communicated over radio, modem or
dedicated serial lines. Today the trend is to put SCADA data on
Ethernet and IP over SONET. For security reasons, SCADA data
should be kept on closed LAN/WANs without exposing sensitive
data to the open Internet.
 Real SCADA systems don't communicate with just simple
electrical signals, either. SCADA data is encoded in protocol
format. Older SCADA systems depended on closed proprietary
protocols, but today the trend is to open, standard protocols and
protocol mediation.
Cont..
 Sensors and control relays are very simple electric
devices that can't generate or interpret protocol
communication on their own. Therefore the remote
telemetry unit (RTU) is needed to provide an interface
between the sensors and the SCADA network. The
RTU (Remote Telemetry Unit) encodes sensor inputs
into protocol format and forwards them to the SCADA
master; in turn, the RTU (Remote Telemetry Unit)
receives control commands in protocol format from
the master and transmits electrical signals to the
appropriate control relays.
Data Presentation
 The only display element in our model SCADA system is the light that comes
on when the switch is activated. This obviously won't do on a large scale - you
can't track a light board of a thousand separate lights, and you don't want to
pay someone simply to watch a light board, either.
 A real SCADA system reports to human operators over a specialized computer
that is variously called a master station, an HMI (Human-Machine Interface) or
an HCI (Human-Computer Interface).
 The SCADA master station has several different functions. The master
continuously monitors all sensors and alerts the operator when there is an
"alarm" - that is, when a control factor is operating outside what is defined as
its normal operation. The master presents a comprehensive view of the entire
managed system, and presents more detail in response to user requests. The
master also performs data processing on information gathered from sensors - it
maintains report logs and summarizes historical trends.
 An advanced SCADA master can add a great deal of intelligence and
automation to your systems management, making your job much easier.
Control
 Unfortunately, our miniature SCADA system monitoring the widget fabricator doesn't
include any control elements. So let's add one. Let's say the human operator also has a
button on his control panel. When he presses the button, it activates a switch on the
widget fabricator that brings more widget parts into the fabricator.
 Now let's add the full computerized control of a SCADA master unit that controls the
entire factory. You now have a control system that responds to inputs elsewhere in the
system. If the machines that make widget parts break down, you can slow down or stop
the widget fabricator. If the part fabricators are running efficiently, you can speed up the
widget fabricator.
 If you have a sufficiently sophisticated master unit, these controls can run completely
automatically, without the need for human intervention. Of course, you can still
manually override the automatic controls from the master station.
 In real life, SCADA systems automatically regulate all kinds of industrial processes. For
example, if too much pressure is building up in a gas pipeline, the SCADA system can
automatically open a release valve. Electricity production can be adjusted to meet
demands on the power grid. Even these real-world examples are simplified; a full-scale
SCADA system can adjust the managed system in response to multiple inputs.
A Brief Note on Sensors and
Networks
 Sensors and control relays are essentially commodity items.
Yes, some sensors are better than others, but a glance at a
spec sheet will tell you everything you need to know to
choose between them.
 An IP LAN/WAN is the easiest kind of network to work
with, and if you don't yet have LAN capability throughout
all your facilities, transitioning to LAN is probably one of
your long-term goals. But you don't have to move to LAN
immediately or all at once to get the benefits of SCADA.
The right SCADA system will support both your legacy
network and LAN, enabling you to make a graceful, gradual
transition.
What to Look for in a SCADA RTU
(Remote Telemetry Unit)?
 Your SCADA RTUs need to communicate with all your on-site
equipment and survive under the harsh conditions of an industrial
environment. Here's a checklist of things you should expect from a
quality RTU:
 Sufficient capacity to support the equipment at your site … but not
more capacity than you actually will use. At every site, you want an
RTU (Remote Telemetry Unit) that can support your expected growth
over a reasonable period of time, but it's simply wasteful to spend your
budget on excess capacity that you won't use.
 Rugged construction and ability to withstand extremes of
temperature and humidity. You know how punishing on equipment
your sites can be. Keep in mind that your SCADA system needs to be
the most reliable element in your facility.
 Secure, redundant power supply. You need your SCADA system up
and working 24/7, no excuses. Your RTU (Remote Telemetry Unit)
should support battery power and, ideally, two power inputs.
Cont…
 Redundant communication ports. Network connectivity is as
important to SCADA operations as a power supply. A secondary serial
port or internal modem will keep your RTU (Remote Telemetry Unit)
online even if the LAN fails. Plus, RTUs with multiple communication
ports easily support a LAN migration strategy.
 Nonvolatile memory (NVRAM) for storing software and/or firmware.
NVRAM retains data even when power is lost. New firmware can be
easily downloaded to NVRAM storage, often over LAN - so you can
keep your RTUs' capabilities up to date without excessive site visits.
 Intelligent control. As I noted above, sophisticated SCADA remotes
can control local systems by themselves according to programmed
responses to sensor inputs. This isn't necessary for every application,
but it does come in handy for some users.
 Real-time clock for accurate date/time stamping of reports.
 Watchdog timer to ensure that the RTU (Remote Telemetry Unit)
restarts after a power failure.
What to Look for in a SCADA
Master?
 Your SCADA master should display information in the most useful ways to
human operators and intelligently regulated your managed systems. Here's a
checklist of SCADA master must-haves:
 Flexible, programmable response to sensor inputs. Look for a system that
provides easy tools for programming soft alarms (reports of complex events
that track combinations of sensor inputs and date/time statements) and soft
controls (programmed control responses to sensor inputs).
 24/7, automatic pager and email notification. There's no need to pay
personnel to watch a board 24 hours a day. If equipment needs human
attention, the SCADA master can automatically page or email directly to repair
technicians.
 Detailed information display. You want a system that displays reports in
plain English, with a complete description of what activity is happening and
how you can manage it.
 Nuisance alarm filtering. Nuisance alarms desensitize your staff to alarm
reports, and they start to believe that all alarms are nonessential alarms.
Eventually they stop responding even to critical alarms. Look for a SCADA
master that includes tools to filter out nuisance alarms.
Cont…
 Expansion capability. A SCADA system is a long-term
investment that will last for as long as 10 to 15 years. So you need
to make sure it will support your future growth for up to 15 years.
 Redundant, geo diverse backup. The best SCADA systems
support multiple backup masters, in separate locations.. If the
primary SCADA master fails, a second master on the network
automatically takes over, with no interruption of monitoring and
control functions.
 Support for multiple protocols and equipment types. Early
SCADA systems were built on closed, proprietary protocols.
Single-vendor solutions aren't a great idea - vendors sometimes
drop support for their products or even just go out of business.
Support for multiple open protocols safeguards your SCADA
system against unplanned obsolescence.
Why is SCADA so popular?
 The major attraction of SCADA to a municipality is the ability to significantly
reduce operating labor costs, while at the same time actually improve plant or
regional system performance and reliability. Information gathering within a
plant no longer requires personnel to spend time wandering all over the site,
and correspondingly the frequency of field site inspections required in a
regional system can be minimized.
 Costly after-hours alarm call-outs can often be avoided since a SCADA system
will indicate the nature and degree of a problem, while the ability to remotely
control site equipment may permit an operator at home to postpone a site visit
till working hours. SCADA based alarming is also very reliable since it is in-
house and tied directly to process control.
 A significant feature of a SCADA system, often not fully appreciated, is the
trending of data and nothing comes close for speed and ease of operation.
When graphically displayed, accumulated operating data often will indicate a
developing problem, or an area for process improvement. Reports can easily be
generated from this data utilizing other common software programs.
 It should be appreciated that while a SCADA system is often complex to
configure - it is extremely easy to operate!
What is involved?
 There are five phases to creating a functional SCADA
system:
 Phase 1
The DESIGN of the system architecture. This includes all
important communication system, and with a regional
system utilizing radio communication often involves a
radio path survey. Also involved will be any site
instrumentation that is not presently in existence, but will
be required to monitor desired parameters.
 Phase 2
The SUPPLY of RTU, communication and HMI equipment,
the latter consisting of a PC system and the necessary
powerful graphic and alarm software programs.
Cont…
 Phase 3
The PROGRAMMING of the communication equipment
and the powerful HMI graphic and alarm software
programs.
 Phase 4
The INSTALLATION of the communication equipment
and the PC system. The former task is typically much more
involved.
 Phase 5
The COMMISSIONING of the system, during which
communication and HMI programming problems are
solved, the system is proven to the client, operator training
and system documentation is provided.
Why You Need Help With Your
SCADA Implementation?
 Implementing an SCADA system can seem deceptively easy - you
just look on the Web, find a few vendors, compare a few features,
add some configuration and you're done, right?
 The truth is, developing a SCADA system on your own is one of
the riskiest things you can do. Here are some of the typical
problems you might face if you don't get expert advice when
you're designing your system:
 1. Implementation time is drawn out: It's going to take longer
than you think. Network monitoring is a highly technical
subject, and you have a lot to learn if you want a successful
implementation. And anytime you are trying to do something
you've never done before, you are bound to make mistakes -
mistakes that extend your time and your budget beyond their
limits.
Cont…
 2. Resources are misused: If you're not fully informed
about your options for systems integration, you may
replace equipment that could have been integrated into
your new system. Rushing into a system wide replacement
when you could have integrated can cost you hundreds of
thousands of dollars.
 3. Opportunities are missed: If you install a
new SCADA system today, you're committing your
company to that system for as long as 10 to 15 years. Many
companies design what they think is a state-of-the-art
SCADA system - and then find that their technology is
actually a generation behind.
DCS vs. SCADA in Modern
Environments
 There is considerable confusion today about the difference
between DCS ("Distributed Control Systems") and SCADA ("Site
Control And Data Acquisition") systems. As you can tell from
expanded acronyms above, SCADA includes "Data Acquisition"
in addition to "Control". DCS, on the other hand, contains only
"Control".
 Understanding why this difference exists requires a 15-second
history lesson. Historically, when computer networks either did
not yet exist or had very low bandwidth, a SCADA system was
the top-level controller for many lower-level intelligent agents. It
was simply impractical to have a single system controlling every
minute aspect of a system. In this technical environment, DCS
devices did most of the detail work and simply reported to (and
took high-level orders from) the SCADA system.
Cont…
 Today, computer networks have become so fast that
there's no practical reason for SCADA and DCS to be
separate. That's why they have blurred together into a
single monitoring and control system. The choice of
name - SCADA vs. DCS - largely depends on the region
where you work. Some areas favor SCADA, others favor
DCS. Occasionally, some people who worked with the
systems before they effectively merged or who have
moved from another region will use a term different
than their coworkers. This again leads to confusion
when new employees must learn to
manage SCADA/DCS.
SUMMARY
(SCADA vs. DCS)
 DCS is process oriented, while SCADA is data acquisition
oriented.

 DCS is process state driven, while SCADA is event driven.

 DCS is commonly used to handle operations on a single

locale, while SCADA is preferred for applications that are
spread over a wide geographic location.

 DCS operator stations are always connected to its I/O,

while SCADA is expected to operate despite failure of field
communications.
References
 www.dpstele.com
 www.pacontrol.com
 www.edaboard.com
 www.instrumentations.blogspot.com
 www.controlengeurope.com
 www.differencebetween.net