Author: Bob Halgren To be successful, an automation project requires automation engineers and design engineers to evaluate the application requirements first, and then select the most effective control system platform. These decisions will have a long-term impact on the operating performance of the plant. In some cases, the impact can be as long as 25 years or more. The majority of control system decisions can be attributed to the selection of programmable logic controllers (PLCs) or distributed control systems (DCSs). Sometimes, a choice is very suitable for a factory, but in other cases, it may not apply. The more factors that are taken into consideration when choosing a control system, the more likely it will be to help achieve short-term and long-term goals. The control system platform will have a certain impact on the way automation systems meet the needs of optimizing production, maintaining availability, and obtaining data. Lack of foresight in the selection of control systems may also affect future expansion, process optimization, customer satisfaction, and company profits. In addition to some basic guidelines (such as how to control the process), the design team must also consider various factors such as installation, scalability, maintenance, and maintenance. At present, although the PLC system may be the most cost-effective for small devices, the DCS system provides more economical scalability and is more likely to obtain a higher initial return on investment. PLC is an industrial computer used to control manufacturing processes such as robotics, high-speed packaging, bottling, and motion control. Over the past 20 years, PLC has added more features and created more benefits for smaller plants and installations. The PLC is usually a stand-alone system, but it can also be integrated with other systems and communicate with each other. Since each PLC has its own database, integration requires some degree of mapping between controllers. This makes the PLC particularly suitable for small applications that do not have much need for expansion. The DCS system distributes the controllers in the automation system and provides common interfaces, advanced control, system-level databases, and easy-to-share information. Traditionally, DCS is mainly used in process technology and relatively large plants. Large-scale system applications are easier to maintain throughout the life cycle of a plant. PLC and DCS systems are generally suitable for discrete and process manufacturing. Discrete manufacturing facilities using PLC systems are generally made up of separate production units and are mainly used to complete the assembly of components such as labeling, filling or grinding. Process manufacturing facilities, often using automated systems, are produced in a continuous and batch process according to recipes rather than parts. Large-scale continuous processing equipment, such as refineries and chemical plants, use the DCS automation system. Hybrid applications usually use both the PLC system and the DCS system. Choosing a controller for an application requires consideration of many factors such as the scale of the process, scalability and future update plans, integration requirements, functionality, high availability, and return on investment throughout the life of the facility. Process sizing: How many input/output (I/O) points are needed? Small systems (<300 I/O points) may have less budget, so a PLC system is more suitable. It is not easy to apply the DCS system to smaller projects. On the contrary, it can play its role in large-scale factory applications. With a global database, DCS systems are easier to manage and upgrade, and any changes are global. Upgrade plan: Smaller industrial processes can be applied to PLC systems, but if the process needs to be expanded or upgraded, more PLC hardware and databases need to be added and they need to be maintained separately. This is a time-consuming and laborious process and it is prone to errors. DCS systems are easier to upgrade, such as being able to manage user trust from a central hub, making it easier to maintain and maintain (see Figure 1). Integration requirements: The PLC system is ideal for stand-alone devices. When the factory configures multiple PLC systems, there will be interconnection requirements. This is generally difficult to achieve because it is often necessary to map data using communication protocols. There is no problem with integration, but when there is a need for change, the user's trouble comes: Once a PLC system is changed, it may cause the two PLCs to fail to communicate properly because of the data mapping. For DCS systems, mapping is not needed at all, configuration changes are just a simple process; the controller is the system's own. High availability: The DCS system can provide redundant configurations for processes that require high availability. Redundancy is critical to long-term operation for processes with high availability requirements. Efficiency and ease of implementation of redundancy are key to keeping costs within budget. Functional requirements: Certain industries and facilities require a history database, streamlined alarm management, and a central control room with a common user interface. Some require the integration of manufacturing execution systems (MES), advanced controls, and asset management. The DCS system has these applications built-in (see Figure 2), making it easy to add to automated engineering applications without the need for additional stand-alone servers and without increasing integration costs. In this respect, the DCS system is more economical and can increase productivity and reduce risk. Life Cycle ROI: The demand for facilities varies from industry to industry. For small-scale process engineering, there is no need for expansion or integration with other process areas, so the PLC system has a good return on investment. The DCS system may have higher installation costs, but from the perspective of the entire life cycle, the increase in output and safety benefits brought by the DCS system will offset some of the costs. Balancing short-term needs and long-term visions is critical to operational deterministic improvement of plant operations and maintenance. Distribution Box,Industrial Distribution Box,Electricity Switch Box,Box For Distribution Guangdong Shunde Langzhi Trading CO., Ltd , https://www.langzhielectrical.com
Figure 1: The DCS system architecture with a single database allows users to maintain and operate the system from a central control station. This image source: Emerson Process Control 
Figure 2: Each system platform has unique database requirements.