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ESD — Emergency Shutdown System. The ESD emergency shutdown system operates in accordance with the principle of safety independence; it is separate from the DCS distributed control system, and its safety level is higher than that of the DCS. Under normal conditions, the ESD system remains in a static state and requires no human intervention. As a safety protection system, it operates above the production process control to monitor the safety of the devices in real time. Only in the event of an emergency in the production equipment is it not necessary to go through the DCS system; instead, the ESD directly sends out protection interlock signals to safeguard the on-site equipment and prevent the spread of danger from causing significant losses. According to available data, people’s judgment and actions in dangerous situations are often delayed and unreliable; when operators are faced with a life-threatening situation, they must react within 60 seconds, and the probability of making a wrong decision is as high as 99.9%. Therefore, it is highly necessary to install safety interlocks that are independent of the control system; this is an important principle for ensuring safe production. It moves when it should move and stays still when it shouldn’t – this is a notable feature of the ESD system. Why is it necessary to have an ESD system set up separately? Of course, general safety interlock protection functions can also be implemented by a DCS. However, for larger-scale emergency shutdown systems, they should be installed separately from the DCS in accordance with the principle of safety and independence. There are several main reasons for this: (1) to reduce the likelihood of both control functions and safety functions failing simultaneously, so that a malfunction in the DCS does not put the safety protection system at risk; (2) for large-scale installations or rotating mechanical equipment, the faster the response time of the emergency shutdown system, the better. This helps to protect the equipment and prevent accidents from escalating ； It also helps in identifying the causes of accidents and keeping records of them. Since DCS processes a large amount of process monitoring information, its response speed is difficult to make fast ； (3) The DCS system is a process control system that is dynamic and requires frequent manual intervention, which may lead to human-induced errors ； ESD, on the other hand, is static and does not require human intervention; by setting it this way, human errors can be avoided. SIS (Safety Instrumented System): A safety instrumented system primarily used in high-speed operating equipment such as turbines and compressors. It monitors parameters such as the speed, vibration, displacement, and temperature of bearings in order to protect the equipment. Originally, it was designed as a combination of modules, functioning essentially as a combination with intelligent instruments. SIS is a safety instrumented system, and ESD is an emergency shutdown system; ESD is part of SIS. SIS consists of field instruments, logic processors, and actuators, all of which must be designed with safety in mind. A conventional ESD system is merely the logic processor part of SIS, which, of course, also needs to be designed safely. A PLC, or Programmable Logic Controller, can be considered an embedded controller when it is used in specialized equipment. However, compared to ordinary embedded controllers, PLCs offer higher reliability and better stability. In practical work, some users who originally used embedded controllers are now gradually replacing them with general-purpose PLCs or custom PLCs.