SCADA, DCS and PLC between the comparison!

With manufacturing enterprises stepping up the planning, implementation and transformation of intelligent factories, how to choose the appropriate industrial automation and control system based on cost and demand is an urgent realistic demand. For the same industrial control applications, different solutions may be proposed.

With the improvement of intelligent application of industrial enterprises, more and more people have come into contact with various industrial automation systems and products, including SCADA, DCS and PLC.

Among them, SCADA that data acquisition and monitoring system is the core of industrial control system, mainly for the control of distributed assets in order to carry out the same as the control of the same important data collection.

DCS is a distributed control system that is mainly used to control the production process in the same geographical location of the system.

PLC, as an important control component, is usually used in SCADA and DCS systems to realize the specific operation and process control of industrial equipment and provide local process management through loop control.

It can be seen: SCADA, DCS is a system, and PLC is a product, PLC can form SCADA, DCS.

DCS and SCADA system comparison

Both DCS and SCADA are system-level solutions consisting of many hardware and software systems. From the system structure, both belong to the distributed industrial control system, with decentralized control, centralized management features. And usually has at least two layers of network structure. Early SCADA and DCS all adopted a special protocol, but at present they basically adopt a unified international standard. But in addition, SCADA and DCS in technology and application there is a big difference.

1, DCS is a kind of technology, SCADA focuses on function and integration.

SCADA system according to the production process monitoring requirements from the market to purchase a variety of automation products and build to meet customer requirements of the system. Because of this, SCADA is very flexible to build and has a great selection of products and solutions. SCADA system will sometimes become DCS, mainly in this type of system also has decentralized control, centralized management features. However, as SCADA system hardware and software control equipment from many different manufacturers, unlike DCS, the main equipment comes from a DCS manufacturer. Therefore, it is inappropriate to call a SCADA system DCS.

2, DCS has a more mature and perfect architecture, system reliability and other performance more secure, and SCADA system is user-integrated.

Therefore, its overall performance is closely related to the user's level of integration, usually lower than DCS. It is because DCS is a dedicated system, DCS open than SCADA poor.

3, DCS is mainly used to control the industrial process with high precision and centralized control point, such as petroleum, chemical industry, metallurgy, power station and so on.

SCADA is mainly used for the monitoring and control of a wide range of production and process control equipment or equipment monitoring, monitoring and control sites are usually no one or less people under normal circumstances, such as mobile communications base stations, long-distance oil pipeline remote monitoring, environmental monitoring. Usually each site I / O points is not too much. In general, the control requirements of field devices in SCADA systems are lower than the requirements of controlled objects in DCS. In some SCADA applications, only remote data acquisition is required without field control requirements.

4, the market size is different.

As DCS is a complete system, equipment and software licensing costs are high, if the number of I / O points less than 100 points, DCS single point of higher cost. The SCADA system used in the controller, the control point configuration more flexible, you can select the appropriate controller according to the number of I / O points. As a result, the cost of choosing SCADA is relatively low for systems with fewer base points.

SCADA, DCS and PLC comparison

1, DCS has the upper computer and the lower computer, the upper computer includes the engineer station, the operator station, the lower position machine includes the scene control station; The SCADA system only on position machine, including the SCADA server and the client machine; But the PLC composition system does not have the position machine, Its main function is on-site control, often use PLC as SCADA system of the next crew equipment. Therefore, PLC can be regarded as part of SCADA system.

2, from the system size, PLC main advantage is logic control, can be used in the control points from a few to tens of thousands of points. The DCS, SCADA is mainly used for large-scale continuous process control. However, in recent years, with the continuous development of technology, various control systems integrate with each other and absorb the functions of other systems. The logic control functions of DCS and the continuous control functions of PLC are constantly enhanced. The functional boundaries of DCS, SCADA and PLC are also Gradually blurred.

3, DCS is mainly used for process automation, PLC is mainly used for factory automation (production line), SCADA mainly for the needs of a wide area, such as the oil field, stretching thousands of miles of pipeline. From application functions, DCS often requires 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.

With manufacturing enterprises stepping up the planning, implementation and transformation of intelligent factories, how to choose the appropriate industrial automation and control system based on cost and demand is an urgent realistic demand.

For the same industrial control applications, different solutions may be proposed. Personally think that, for the control point is widely distributed control process, give priority to SCADA system. For a more focused continuous process control needs, such as process industries, give priority to DCS systems. For on-site process control choose PLC. However, in the actual implementation and application process, companies still need to fully assess the needs and costs of a flexible choice.