Based On Industrial Control System And Using PLC
Components of industrial control system(ICS) can be divided into control center equipment and remote field equipment according to different locations.
The control center equipment is located in the system control center, including human-machine interface(HMI), engineer workstation and records.
Remote field devices are devices that reside on the production site and connect directly to drivers and sensors. The main function is to monitor and control physical processes.
Field equipment usually does not interact with people directly, but the production site is not as secure as the control center, so it is more vulnerable to attack and damage.
Human computer interface(HMI), also known as SCADA system, is a system where operators can monitor and control processes.
Human computer interface(HMI) programs are usually pure software applications running on ordinary computers running in the Microsoft Windows operating system environment. Common HMI projects in the industrial field include Wonderware, Siemens WinCC, Rockwell RSView and Areva E-terra.
Historian is a database server that records the status of the process control system. In some cases, if the history is strong enough, it can also be used as the HMI of the control system. The history server Historian usually runs on mainstream operating systems and conventional hardware devices, and usually performs image backup on the enterprise network.
Remote workstation equipment includes PLC, RTU, IED and relay. The functions of these devices are very different, but can be roughly combined according to location and similarity.
In addition, these devices usually use similar hardware structures to provide analog or digital I/O and control functions. They read data directly from the sensor and send operation commands to the operator. Sometimes connected to other field devices.
This article simplifies the equipment. In fact, the above devices(PLC, RTU, IED and electronic relay) perform a specific subset of functions in the object relational model(ORM) of the control system.
For example, RTU is a SCADA system and usually only provides field I/O control. The sampling is completed by the field I/O sensor. The RTU creates the trigger separately on the initiator.
The electronic relay always performs sampling and triggering functions. RTU creates status data field points and sometimes processes command data field points. The relay generates the status data field points, but cannot process the data field points of the command. The RTU usually has no local control function, but the relay has this function. In addition to communicating with sensors, actuators and upper control functions, PLC also has important local control functions. These functions look similar, but are very different in ORM.
The general commercial PC running HMI communicates with field devices(such as PLC) through standard network protocols such as Ethernet. Engineering workstations and historical databases are also general-purpose commercial PCs or servers that communicate with field devices through standard network protocols. Fieldbus and other Ethernet based industrial control protocols are used to connect field devices to other field devices. Some field devices use RS232 or RS485 standard serial bus communication protocol to connect to intelligent devices. Some field devices are directly connected to sensors, I/O devices, and mechanical devices.
The PLC is a field device that can be directly connected to sensors and drivers or other field devices. The PLC is usually controlled locally by a logic program in the format defined in the IEC61131-3 standard, and can receive control commands and query requests from the HMI through the control system communication protocol. PLC can be combined into modular or compact fixed form, but the same basic components are used by default.