The development process of safety control system mainly depends on the development process of logic control unit. The development of logic control unit has gone through a process from simple to complex, from low level to high level, just like the domainization of human beings. From simple relays to solid-state circuit logic systems, and then to safety control systems with microprocessors as the core.
The advent of relays in 1863 formed the world's first safety control system with relays as the core component. This safety control system has lasted for more than 100 years until 1969 when the American Digital Equipment Corporation (DEC) developed the world's first PDP-14 PLC, creating a new era of using programming methods for industrial control. In 1975, Honeywell first launched the first generation of distributed control system (DCS), namely TDC-2000 system, based on the problems of PLC for discrete control. Since then, the development direction of control system has been divided into two lines: the development process of PLC control system; the development process of DCS control system.
Development of PLC control system
According to the capacity, I/O points and scanning speed of PLC, the development process of PLC can be divided into three stages.
Phase 1: PLC capacity is small, I/O points are less than 120 points, and the scanning speed is 20 to 50 ms/kB. The PLC control system at this stage only has some simple logic operations, timing, and counting functions.
Phase 2: PLC capacity has been expanded, I/O points have reached 512 to 1 024 points, and the scanning speed is 5 to 6 ms/kB. At this time, in addition to the functions of the PLC control system in the first stage, the PLC control system has also added arithmetic operation instructions, comparison instructions, analog quantity control and ladder diagram programming language.
Phase 3: With the continuous expansion of the scale of integrated circuits, PLC control systems composed of 16-bit and 32-bit microprocessors have been further developed. At this time, the PLC capacity was very large, and the I/O points of large PLC control systems reached 4,000 to 8,000 points, with a scanning speed of 0.47ms/kB. On the basis of the second stage, arithmetic floating-point operation instructions, PLC adjustment function instructions, graphic configuration function instructions, network, communication instructions and sequential function language were added.
Development of DCS control system
Since Honeywell developed the first DCS control system in 1975, as people's requirements for DCS continue to increase, the development of DCS control system has gone through 4 generations.
First generation: launched between 1975 and 1980, the design focus of the DCS control system at this time was the field control station. The systems developed by various companies all used the most advanced microprocessors to form the field control station. The DCS of this period was very close to the instrument control system in terms of function.
Second generation: launched around 1980-1985, it introduced the local area network as the system backbone, began to get rid of the influence of instrument control, and gradually moved towards a computer system. At this time, the DCS control system has more complete functions, and has realized some optimization control and production management. At the same time, people can learn more about the production site information and control system information in the control room.
The third generation: marked by the I/A Series launched by Foxboro in 1987. All manufacturers have adopted the five configuration languages defined by IEC61131-3 in configuration, overcoming the "automation island" phenomenon that appeared in the second generation of products and realizing data connectivity between products produced by different manufacturers.
The fourth generation: appeared in the early 1990s. The DCS control system at this time is characterized by integrated management and control. It can well solve the centralized management of the DCS system and the management and communication of information.
