(1) Distributed control systems (DCS) are digital control systems that connect field instruments like sensors to computers and human-machine interfaces. They are used in industrial processes to monitor and control distributed equipment. (2) SCADA systems focus on supervisory control and data acquisition from a central location rather than full control. They are software packages that interface with hardware controllers. (3) Historically, DCS controlled processes locally while SCADA provided higher-level control, but modern networks have blurred the distinction between the two terms which are now often used interchangeably.

1. BY:
Sahil Ahmad
Roll no - 2100430519003
Bundelkhand Institute of Engineering & Technology Jhansi UP

2. 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.

3. 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 Chemical engineering applications to monitor and
control distributed equipment with remote human
intervention.

4. 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.

5. 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.

6. 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.

7. Distributed Control System

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. References
 www.dpstele.com
 www.pacontrol.com
 www.edaboard.com
 www.instrumentations.blogspot.com
 www.controlengeurope.com
 www.differencebetween.net