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.
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