Before
starting the judgement between the two, let’s start with what is actually the
meaning of those electronics terms. First is DCS, the abbreviation of
Distributed Control System and second, PLC, the abbreviation of Programmable
Logic Controllers.
Distributed Control
System
A Distributed Control System (DCS) refers to a computerized control
system used to control the production line in the industry, usually of a
manufacturing system, in which the controller elements are distributed
throughout the system. The entire system of controllers is connected by
networks for communication and monitoring.
Programmable Logic
Controller
After knowing what is the meaning of DCS, then what is PLC? PLC
(Programmable Logic Conntroller) is a digital computer used for automation of
electromechanical processes, such as control of machinery on factory assembly
lines, amusement rides, or light fixtures.
Find
any silver lining from the explanation above? Obviously not. To know what kind
of automation system that suited your application of course you should take a
look at its criteria. For easy understanding, let us simplify into the analogy
of automobile. In the past you had two kind of cars, it is sedan and pick-ups.
And now, you have a whole range of cars, starting from pick-ups, SUVs, cross
over, sedan, and etc. You can find any option between those two levels. A
similar situation now exist the world of controller.
Analog I/O VS Discrete I/O and Speed
High speed application like packaging line,
with a large amount of discrete I/O is clearly a PLC application. While for the
distributed control systems (DCS) that are mosltly used in large company, such
as food & beverage, biofuels, brewing, chemical steel, nuclear, and
pharmaceutical industries require a large amount of analog I/O and required
distributed architecture and multiple controllers. DCSs are connected to
sensors and actuators and use setpoint control to control the flow of material through
the plant. A typical DCS consists of
functionally and/or geographically distributed digital controllers capable of
executing from 1 to 256 or more regulatory control loops in one control box.
Coordination of Control & Alarm Management
One of the advantage of this advance level of
contoller (distributed control syste) is that the engineer could now control
the process without having to understand the equipment necessary to perform the
control functions. Panel boards were no longer required, because
all of the information that once came across analog instruments could be
digitized, stuffed into a computer and manipulated to achieve the same control
actions once performed with amplifiers and potentiometers. And of course, when
it comes to alarm management, that also meant that alarms were easy and cheap
to configure and deploy, because the distributed control systems use architect
to handle some alarms that can handed/presented into necessary/possible
operators to insure:
- Personnel
and Environmental Safety,
- Equipment
Integrity,
- Product
Quality Control
While in PLC system, it has many places to
manage the alarm. It could be in
controller, or even in the HMI (Human Machine Interfere). But since it
used many places to handle the alarm, when the object becomes too large, this
can get quiet complex overtime. That’s why it is more likely to use the DCS
system.
For better understanding, please take a look
at the video below:
And today, much like the automobile, we have
more option available, process PLCs or a small hybrid DCS, just like how the
analogy described. So when selecting the automation system, we as engineer
should take a look at what’s available today. Now there are many more options,
they may better fit for any kind of your application’s requirements to ensure your
success and profitability.
Annisaa Rasyida | 112110098 |
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