Differences between SCADA and DCS, PLC

- Nov 13, 2017 -

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Industrial control system

Industrial control system (ICS) (also called industrial automation and control system) is a general term for various control system types. It consists of various automation control components and process control components that collect and monitor real-time data Industrial infrastructure automation operation, process control and monitoring business process management and control system.

Industrial control systems cover many types of control systems. Among the more common and confusing control systems are SCADA, DCS, and PLC. So, SCADA, DCS and PLC What is the difference between the three?

DCS

DCS system, distributed control system, is mainly used in the same geographical location environment, control the production process of the system.

 

The DCS system uses a centralized monitoring method to coordinate the local controller to execute the entire production process. With a modular production system, DCS reduces the impact of a single failure on the entire system. In many modern systems, there is an interface between the DCS system and the enterprise system to enable the production process to be reflected in the overall operation of the business.

DCS system commonly used in oil refining, sewage treatment plants, power plants, chemical plants and pharmaceutical and other industrial areas. These systems are commonly used in process control or discrete control systems.

SCADA

SCADA system, the data acquisition and monitoring system, is the core system of industrial control. It is mainly used to control the scattered assets for centralized data acquisition which is as important as control.

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SCADA systems integrate data acquisition systems, data transfer systems and HMI software to provide centralized monitoring and control for process inputs and outputs. The SCADA system is designed to collect live information, transmit the information to a computer system, and present the information in graphical or textual form. Thus, an operator can monitor and control the entire system in real time from a centralized location, control any single system according to each system's complexity and related settings, and automatically perform related operations or tasks, which can also be ordered by an operator Executed automatically.

SCADA systems are primarily used in distributed systems such as water treatment, oil and gas pipelines, power transmission and distribution systems, railways and other public transportation systems.

PLC

PLC system, programmable logic controller. PLC is a new type of industrial control device which is formed on the basis of the traditional sequential controller by introducing microelectronic technology, computer technology, automatic control technology and communication technology. The aim is to replace the relay, logic implementation, timekeeping, counting, etc. Sequence control function, the establishment of flexible program-controlled system. International Electrotechnical Commission (IEC) promulgated the provisions of the PLC: programmable logic controller is a digital computing operation of the electronic system, designed for industrial applications and design. It uses programmable memory to store instructions for operations such as logic operations, sequence control, timing, counting, and arithmetic operations in its internal memory and to control various types of inputs through digital and analog inputs and outputs Mechanical or production process. Programmable logic controller and related equipment, should be easy to form a whole with the industrial control system, easy to expand its functional design.

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In the industrial automation and control system network architecture, PLC as an important control component, usually used in SCADA and DCS systems, used to achieve the specific operation of industrial equipment and process control, loop control to provide local process management.

In a SCADA system, the function of the PLC is the same as that of the RTU (remote terminal unit). When used in a DCS system, the PLC is used as a local controller with a monitoring control plan. At the same time, PLCs are often used as control systems for smaller components of critical components. PLCs have user-programmable memories for storing instructions that implement specific functions such as I / O control, logic, timing, counting, PID control, communication, arithmetic, data and file processing. With the development of communication technology, PLC also switched from a closed private communication protocol to an open public protocol, greatly improving system compatibility and facilitating system maintenance and updating.

to sum up 

It is easy to see from the above:

SCADA, DCS is a concept, and PLC is a product, the three are not comparable:

1, PLC is a product, it can form SCADA, DCS;

2, DCS is the development of process control, PLC is a relay - logic control system developed;

3, PLC is equipment, DCS, SCADA is the system.

Narrowly speaking, DCS is mainly used for process automation, PLC is mainly used for factory automation (production line), SCADA mainly for wide area needs, such as the oil field, stretching thousands of miles of pipeline. If from a computer and network perspective, they are uniform, the reason why there are differences, mainly in the application needs, DCS often require advanced control algorithms. For example, in the oil refining industry, PLCs require high processing speed. Because they are often used in interlocking and even fail-safe systems, SCADA has some special requirements such as vibration monitoring, flow calculation, peak shaving and so on.

Therefore, we can simply think:

DCS

DCS

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