Home Business Insights & Advice Important distinctions between DCS systems and PLC systems

Important distinctions between DCS systems and PLC systems

by Ben Jones
4th Nov 22 12:25 pm

Industries with multi-layer systems that involve the transmission of signals or information to operate use Distributed Control Systems (DCS). The Distributed Control System (DCS) and Decentralized Control System (DCS) are sometimes used interchangeably. Nowadays, a DCS system is also used for low-level control loops and advanced control processes. For example, you might have seen the process of an oil refinery where many controllers are placed to control the flow from the valves. They are closed-looped controllers that operate and control the valves. DCS systems are responsible for all the processes.

Talking about other controllers used for industrial automation are Programmable Logic Controllers (PLC). They are used for handling single processes and repetitively for discrete control, but DCS is used for handling multiple machines that manage continuous operations. Both the DCS & PLC systems are used for a similar process, but there are a few differences that we will discuss further in the article.

Overview of DCS systems and PLC systems

Earlier the control system relied on relays and contractors to function. You might think the DCS system has replaced the PLC system, but it is nothing like that. Instead, both these systems coexist and enhance the functionality of the factory or plant. The PLC usage has increased due to limitations of old systems like flexibility and excessive time to fix the issues. The consumer needed something efficient to reduce the downtime and work well in the system of loose wires, dirty connections, and more. In this situation, the PLC system came as a saviour.

Everything was going at a decent pace, and a substantial change occurred. A computer replaced the analogue control system that performed all the control tasks in place of the analogue control system. As a result, the Direct Digital Control (DDC) concept became more cost-effective and efficient than earlier. It has been a revolutionary step where a centralised system controls everything. But in a few years, the domination of IT firms like Microsoft, and IBM marked it clear that software-oriented machines are the future. The below section will discuss the differences between the DCS and PLC systems.

Difference between DCS systems and PLC systems

PLC stands for Programmable Logic Controller, and DCS stands for Distributed Control Systems. PLC is a logical controller, whereas DCS is a system with multiple controllers distributed over the plant. With the advancement of technology and the innovation of new products, there are a few more differences that you must know about DCS and PLC.

Parameters of Comparison Programmable Logic Controllers (PLC) Distributed Control Systems (DCS)
Architecture of the System It consists of controllers, IO modules, HMIs, and software for processing. Making it a flexible controller. In comparison with PLC, it is less flexible with IO systems, controllers, databases, and operating servers.
Speed of Response of the System Its speed of response is one-tenth of a second. DCS are slower than PLC with a 30ms response time.
Logic Development It is programmable as per the requirements It comes with an in-build control function.
Cost of the System It is less expensive It has updated architecture, so it is expensive
IO Capacity of the System It can handle hundreds of IOs with 10 analog IOs. It can handle thousands of IOs.
Scope of Working PLCs are for applications that change less often. It is suitable for complex processes.

Points chimed in for you

In the case of PLC based system, if it is damaged, the whole operation you are working on will be discontinued. On the other hand, in a DCS, multiple independent controllers ease the system processing without any disturbances. Therefore, if you are looking for a DCS or PLC system, you must go for the remote monitoring and supervision expert.

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