What is DCS? What are the Differences Between DCS and PLC Systems?

What is DCS?

Distributed Control System (DCS) generally refers to the control system of a process or production system in which the sensor, controller elements and associated computers are distributed throughout the system. It is controlled by one or more controllers in the system, serving the unique purpose of data acquisition, process control, data storage, and graphical display.

Process plants had long panel panels Single Loop Controllers (Analog / PID controllers). DCS, the 'central brain' of the facility, makes automated decisions based on manufacturing trends, as it sees it in real time at the manufacturing facility.

While DCSs are used in industry to control complex automation processes, they are more commonly used in large and continuous production facilities such as in the petrochemical industry.

Similarities And Differences Between DCS AND PLC

1.Functional Blocks are also available in DCS and PLC systems.

2.DCS system takes care of loop scheduling of Functional Blocks which are basic execution units.

This is comparatively faster overall scan time of DCS than PLC system. This functionality has also been introduced in PLC systems in some ways.

3.PLCs are still used in RTU stations due to their small and inexpensive architecture and engineering (typically RTU implementation) rather than large DCS .

DCS was used as the central system in a SCADA network. In a typical SCADA scenario, one DCS is connected to several PLC systems.

4.PLC's functionality has evolved over the years, including sequential relay control, motion control, process control, distributed control systems, and networking.

However, in large industrial areas and building markets it is practical to use DCS for process control and PLC-based system for safety control.

PLC vs DCS

DCS integrates one or more PLCs into the automation system by combining them with an HMI. The project is usually developed with the whole DCS in mind so that all aspects of the system are developed together A DCS takes the PLC/HMI combo and combines some other features in an integrated package:

• Servers and customers. Servers collect tag data from PLCs, include graphics, and serve customers, both for operators to use.
• Redundant servers, controllers and/or networks.
• Historical data record and trend.
• Synchronized alarm and security.
• Process
• Party management.

What Are the Benefits of a DCS?

In addition to combining one or more PLCs with one or more HMIs, a DCS offers:

• High availability with:
  • Control Units with Redundancy
  • operator system servers Redundant
  • Redundant networks.
  • Server-client relations.
• Reduced engineering time.
• Minimal troubleshooting of added features.
• Get started sooner.
• Controller code with the whole system in mind. The code includes:
  • HMI graphics and faceplates.
  • Operator features and security
  • historical data
• It rewards itself for better organization and consistency than a PLC / HMI combination.
• It can be easily integrated with:
  • Party management.
  • Historian Process.
  • OPC server.

What Are the Benefits of a PLC?

The biggest benefit I see with a PLC is that it is easier for plant personnel to implement and configure internally than DCS.

There are many technicians and engineers who have experience with ladder logic , and if your staff has one or more, you may decide to take care of yourself inside your processes.

Also, if PLC is controlling a machine that requires very fast response time, PLC would be the best choice. A DCS controller may have a fast response time, but that's not what it was intended for.

Also, purchasing a PLC allows you to only purchase software with the features you need. If you have a simple application or a standalone sled system, a PLC (with small HMI) may be all you need. If you were to buy a DCS, you could end up spending a lot of money on features you don't need.

Finally, in a pinch, a PLC can be set up, programmed and ready to go very quickly.

PLCs are often used like this:

• The sleds are standalone systems (not necessarily part of a plant-wide system or developed by an OEM).
• Utilities (low cost).
• Machine automation (faster processing time).

Summary

To summarize briefly, both PLCs and DCS are in the market today. PLCs operate in a small production environment where component failure poses a minor risk to the application if not much system is used, where the budget is constrained.

DCS is better used in an environment with large component counts with lots of continuous operations, DCS also claims to be the most reliable system when safety is the top priority.

This is because the manufacturer provides both control and inspection equipment as an integrated package, greatly reducing the risk of integration errors.