Sunday, April 11, 2021



A distributed control system (DCS) is a decentralized automated control system for monitoring and controlling the functioning of a process or factory. DCS has self-contained controls strewn over the site. Workstations are created by each individual controller that communicates with a central computer. A high-speed communication network links all of the remote controls together. The fundamental benefit of separating control chores is that even if one of the dispersed controllers fails, the plant will continue to run.

Controllers for systems or groups of equipment are given locally in a DCS, but they are networked to one or more workstations in a central location.

To provide some context, when PLCs (programmable logic controllers) were first developed, they were excellent at controlling single processes. They were mostly used for discrete repetitive control. The DCS was created to control a large number of autonomous controllers that perform a variety of continuous activities mostly using analogue control. As a reminder, PLC stands for "programmable logic controller." Processes and machines are controlled by them. To automate machines and processes, they monitor inputs, make control decisions, and direct the functioning of outputs. Prior to the introduction of PLCs, most control applications were controlled by hard-wired relays and contactors. Circuits have to be designed initially, followed by component installation and the creation of a wiring diagram. The system would next be wired together by electricians and specialists. Designers and technicians would have to redesign the entire system if something went wrong or if a change was required. When using PLC, however, the same job may be done without having to overhaul or redesign a system.


There are some fundamental distinctions between DCS and PLC. PLCs began as relay replacements and are now largely used to control discrete manufacturing processes and stand-alone equipment. PLCs were typically employed for single and high-speed control with a design that was reasonably basic and low-cost. The design is adaptable and generic, but it may be customized to your liking. The task processing time was typically quite short. To control the system, operators typically use a graphical display such as SCADA or PID.

For continuous sophisticated controls, DCS is employed. The system's core is an integrated control system that includes SCADA and PID. The DCS comes with a number of pre-programmed functionalities that can be tweaked and deployed for a variety of purposes. When compared to PLC, processing time is slower. An integrated graphical display allows the operator to communicate with the system.

DCS also claims to be the most reliable system when safety is a key consideration. Because manufacturers provide both control and supervisory equipment as a single package, this is the case. There is a significant reduction in the risk of integration errors.

In some cases, a PLC system is the ideal option, such as for smaller operations or when redundant components are used to eliminate the potential of process shutdowns. Due to the nature of a single processor operating an entire plant, you risk production halting without redundancy. PLC or DCS applications can both benefit from redundancy.

DCS would be used for larger and more complicated processes, much as a PLC system might be used in certain cases. It necessitates a great deal of interaction among multiple processors.


The DCS is a closed loop control process oriented system.

1. OPERATOR STATION - In a DCS, the operator stations constitute the system's heart. This is where the operator may monitor the plant's performance, such as new process warnings and alarms, as well as monitor production.

2. Servers, various types of computers, and engineering stations may be found in the next level of component. Industrial ethernet is commonly used for communication with the operator station level. At the processor level, servers are utilized to collect data. They are in charge of the data that travels between the operator station and the plant floor processor.

3.In order to store historical data that could be utilized for trans or compliance, all types of computers are used. Engineering stations are used to create projects on which processes are carried out. Hardware setups, job logic, graphical displays for operator action, and task administration through installed software packages are all included. This is the station where the project is downloaded in graphical form to the processors.

4.Components such as master controllers, which supervise individual processors, and input/output modules are found at the next level. These controllers are also in charge of sending data to the servers, which then send it to the graphical interface. For communication with the previous level, industrial ethernet is commonly employed. When an ethernet cable run is too long, fiber optic cabling may be employed. Processors execute the logic and perform the tasks required to govern the process at this level.

5. Field devices are the next level of components. Nearly any type of device that is compatible with the components can communicate between this level and the processor level. Devices, motors, remote or distributed input/output devices, and other components would be included at this level.

Both PLC and DCS have a role in today's industry. PLC would be best suited to a small manufacturing environment where component failure poses a little danger to the application if no redundant system is in place. The budget is limited, or the task's I/O count is low.

A DCS would be more appropriate in an environment with high I/O counts and numerous continuous processes. The production will not be harmed by a process failure in one component of the facility.

The distinction between PLC and DCS is becoming increasingly blurry, and it may not be long before there is none at all.


The following are some of the benefits of a distributed control system:

1. Minimal effort spent on engineering

2. DCS demonstrates batch management capabilities.

3. There is a need for less troubleshooting on the system.

4. The method itself encourages better organization and dependability.

5. Faceplates and visuals for the Human Machine Interface (HMI) are included.


The DCS is used in the following industrial processes:

1.Nuclear power plants, chemical and petrochemical factories, and metallurgical plants are all areas of application.

3. Food processing industries 

2. Automobile engineering

4. Pharmaceutical manufacturing 5. Water treatment and sewage treatment plants

6. System of environmental management


The following are some of the benefits of PLC: 1. lower size

2. Diagnostics and override functions integrated

3. Duplicating a procedure is easier and less expensive.

4. Changes to the system are made more quickly and easily.


1.      In the glass industry, PLCs are commonly used to regulate material ratios and produce flat glasses. Technology has progressed over time, resulting in a higher demand for PLC control mode in the glass sector.

2.      PLCs are utilized in a variety of operations in the paper industry. Controlling machines that generate paper goods at fast speeds is one of them. In offset web printing, for example, a PLC controls and supervises the creation of book pages or newspapers.

3.      PLC is utilized in automatic beverage filling machines and water filling machines in the food packaging business. It enables the best coordination between various automation systems, resulting in superior results.

4.      It is utilized in the transportation system to control conveyor belts, escalators, and elevators, among other things.

5.       PLC is utilized in the cement industry for manufacturing or mixing the proper quality and amounts of raw materials, as well as data accuracy.

6.       PLC is utilized in an industrial machine's time and count-based control system.

7.       PLC is used in the oil and gas industry to regulate Purging Procedures, as well as Valve Switching for Fuel Changeovers, Pilot Light ON or OFF, Flame Safety Checking, Oil Filtering Procedures, and other tasks.

PLC can be used to automate any commercial or home application as part of the automation process.

PLC aids in the monitoring of input and output devices, as well as the creation of logic-based decisions, automatic sequential counts, and time-based control systems for automated processes. Switches and push buttons, sensing devices, limit switches, proximity sensors, photoelectric sensors, condition sensors, vacuum switches, temperature switches, level switches, and pressure switches are all examples of PLC input devices.

Any piece of hardware used to communicate the outcomes of data processing carried out by a PLC and translate the information into a comprehensible form is referred to as an output device. Valves, motor starters, horns and alarms, stack lights, control relays, pumps, printers, and fans are examples of PLC output devices.


Despite the fact that both distributed control system and programmable logic controllers are monitoring and control devices in industrial installations, their objectives are rather different. In terms of hardware and components, there are some similarities between distributed control system and programmable logic controllers; nevertheless, end-user needs distinguish a robust and cost-effective distributed control system from a stand-alone programmable logic controller system.

Programmable logic controllers dominated machine control in the initial stages of automation, that is, operationss requiring discrete management of automated processes. In applications that has to do with oil, gas and chemical facilities, a distributed control system was the preferred method of process control. For the most part, the separation between a programmable logic controller and a distributed control system still follows this historical trend.

Individual machines are still managed by Programmable Logic Controllers, but in a factory or facility, a Distributed Control System can manage a larger number of equipment or processes. A distributed control system, on the other hand, can monitor and control a large number of machines and processes at the same time. They're typically used to manage entire manufacturing systems.

Programmable Logic Controllers are known for their simple operating systems, which are designed to perform a limited number of tasks, such as receiving input signals and controlling output devices. They can run operations quickly due to their  Operating System structure, as there aren't many other operations taking processor time in the background.Because they are physically closer to the equipment they oversee, the processing time of a Programmable Logic Controller appears to be faster, making them more responsive than a bigger Distributed Control System that is controlling many more devices. Programmable Logic Controllers are more adaptable and adjustable than ordinary controllers.



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