What is the difference between RTU, PLC and DCS?

RTU , as a remote logic control unit that succeeded PLC, has gradually been recognized by the industry with its outstanding performance in wide-area applications. It has also attracted a group of automation manufacturers with forward-looking strategic vision. Conducted professional R&D and manufacturing. This is definitely a new product that is different from PLC. However, some products called RTU currently on the market seem to be more similar to PLC. Although they also have the wide temperature and corrosion resistance characteristics of RTU, their applications cannot be accurately positioned. While people are enthusiastically discussing this new addition to the controller, they are also full of doubts about it.

RTU is the abbreviation of Remote Terminal Unit (remote measurement and control terminal) and is the basic component unit of the SCADA system. SCADA is the abbreviation of Supervisory Control and Data Acquisition. It is a data acquisition and monitoring control system for production systems distributed over long distances and with scattered production units.

Une RTU peut comprendre plusieurs points d'E/S, des dizaines ou des centaines, et peut être placée sur place, à proximité du point de mesure. La RTU a au moins les deux fonctions suivantes : collecte et traitement des données, transmission des données (communication réseau). Bien entendu, de nombreuses RTU disposent également d'une fonction de contrôle PID ou d'une fonction de contrôle logique, d'une fonction d'accumulation de flux, etc.

Remote control unit – RTU, the product concept was proposed in the U.S. oil and gas industry in the early 1880s. RTU products were first produced in the United States and used in North America. With the development of automation in the oil, gas and power industries, RTU products were Universal application.

The development of logic controllers is not a product that dominates the world, nor is it a variety of products blooming at the same time, but a process of continuous innovation with the development of other electronic communication technologies. The earliest PLC was just a logic controller. It was born in Europe and was widely used in the field of lathes with developed industrial automation. At that time, logic control was mainly based on relays. However, with the development of computer electronics technology thirty years ago, PLC has become more powerful. The automation direction of CPU has developed. It can be said that PLC is the earliest history of logic control.

The DCS system was born in the United States. It is equivalent to a decentralized control system. In the past, all instruments of only one machine and equipment were controlled by PLC. Later, the factory developed to have more equipment that needed unified control, and then decentralized control appeared. Finally, unified centralized control was implemented, and the DCS system was produced.

Nowadays, PLC and DCS are getting closer and closer, such as Siemens PLC S300. By the time S400 is reached, it is basically not much different from the DCS of Emerson, Honeywell, and Foxboro. In other words, some industry applications can use either DCS or S400, so S400 is no longer called PLC, but only called controller. Similar products from ABB do not call it PLC or DCS. , also only called the controller.

At present, it is difficult to strictly distinguish between PLC and DCS. In fact, there is no strict boundary between them. In the process of the development of the two, another type of controller RTU was produced, which relies more on the development of communication technology. RTU is more widely used in wide areas, such as oil and gas long-distance pipelines and oil and gas fields. The best application in China is the gas pipeline from Xinjiang to Shanghai in the West-East Gas Pipeline Project. A complete set of controls including the valve pool station and intermediate station are based on the improvement of the communication system. PLC can be used in the station and in the control valve pool. This piece more applications remote control unit RTU. The entire control system is a complete SCADA system.

With the development of SCADA systems and communication systems, RTU has gradually moved towards wider applications, and its market demand has expanded in a short period of time. RTU is a concept that came into existence with the application of PLC. It has open development and more open applications. Especially today with the development of network communication technology, RTU can be applied to many fields that PLC cannot reach. .

There are some differences and connections between PLC and RTU. Generally speaking, RTU is more powerful in terms of industrial communication and environmental adaptability. However, the industry sometimes cannot distinguish between the two because some industry fields can use both PLC and RTU. What we can be clear about is: where PLC can be used, RTU can also be used; where PLC cannot reach, RTU can also be used.

However, in view of their respective special advantages, in the installation of CNC machine tools, industrial manufacturing and other equipment, the advantages of PLC logic control are more preferred in terms of realizing logical control of the entire system and continuous control of logical sequences at limited local distances; In the fields of process control, data collection, information collection, PID control, and analog quantities, RTU has stronger advantages. Because of its stronger storage capacity and wide temperature environment adaptability, all temperature indicators of PLC are 0~50℃, and the temperature indicators of RTU are -40~70℃. This wide temperature indicates that RTU does not need any device protection. Regardless of temperature restrictions, it can work normally under various extremely high and extremely low temperatures in the Gobi Desert or extremely cold zones.

For example, in oil and gas field automation control applications, RTU basically covers the full range of automation control applications from wellheads, metering stations, joint stations, central control rooms to transportation to the outside. Only natural gas stations use DCS. Relatively speaking, the IO points of RTU It only has a few points to a few hundred points, while the IO of DCS has thousands of points. This is its advantage.

RTU and PLC are like two intersecting circles with public and non-common parts. They are not two circles that can completely overlap. The reason why people can’t tell them apart is because they only see the intersection of the two. , in fact, there are clear differences between the two in terms of application scope and product essential technology.