News

On April 10, 2024, the first DCS cabinet of the world’s first commercial modular small reactor “Linglong One” was installed and started the installation and commissioning work. The introduction of the first DCS cabinet of “Linglong One” marked the transition of DCS to the on-site installation stage, laying the foundation for subsequent operations such as the availability of the main control room. The DCS system of “Linglong One” adopts the Chinese-owned intellectual property platforms of “Dragon Scale” (safety level) and “Dragon Fin” (non-safety level). The Dragon Scale platform can achieve reactor safety control under various operating conditions; the Dragon Fin platform is responsible for operation and management. [2]
In November 2025, the DCS system of the Changqing Power Plant Branch of Jinan Thermal Power Group implemented a daily two-times full-range equipment inspection system and a 24-hour duty system during the first heating season. During the critical period of heating preparations, this system handled the fault of oxidation and fracture of the shielding wire of the TSI system of the steam turbine. [4]
Changqing Power Plant has established a safety management system featuring “all-staff participation and full-process control”, and has formulated a learning system of “one learning session per week, one test per month, and one competition per quarter”. The team has set up an online learning platform and invited experts to conduct on-site guidance and training. [4]
On December 3, 2025, the Balaka factory of Huaxin Malawi Company officially went into operation. This factory adopts a DCS automated control system covering the entire process, and manages through intelligent control and low-carbon calcination technology. The factory produces high-end building materials. [5]
In February 2026, the Volatile Organic Compounds (VOCs)综合治理 project of Henan Zhongyuan Dazhao Group’s coal chemical plant, which was constructed by the EPC总承包 team of China Chemical Engineering Third Construction Co.， Ltd.， entered the stable operation phase. During the commissioning process， the technical team optimized the DCS control system and safety interlock logic. This project is a key environmental protection upgrade project in response to the national “carbon neutrality” strategy， aiming to achieve safety， efficiency， and energy conservation of the plant under full-load operation. [11]
In 2026， Shandong Anshun Pharmaceutical Co.， Ltd. equipped its fully automated raw material drug production line with a DCS control system.

The distributed control system has evolved through multiple stages since its inception in the mid-1970s. The core features of each stage are as follows:
Mid-1970s (First Generation)
Representative products included the TDC-2000 from Honeywell, the Spectrum system from Foxboro, the Network-90 system from Bailey, the Teleperm-M system from Siemens, the 900/TX system from Nippon Chuen, and the CENTUM system from Yokogawa. The system mainly consisted of data acquisition devices, field control stations, CRT operation stations, high-speed data communication paths, and monitoring computers. This stage’s products had the advantages of centralized computer control systems, with effective decentralization of control units, and CRT operation stations featuring rich graphics and full system alarm, diagnosis, and management functions. However, the monitoring computer mainly handled many management and information processing functions, using 8-bit or 16-bit microprocessors, with communication being a primary industrial control local network, and the use of a dedicated communication protocol limited system compatibility. Some systems lacked sequential control functions, and the technology had limitations. [6]
Early 1980s and mid-1980s (Second Generation)
Representative products included Honeywell’s TDC-3000, Taylor’s MOD300, Hitachi’s HIACS-3000, Westinghouse’s WDPF, and Yokogawa’s YEWT-TORIA, among others. Some were new designs, while others were upgrades from the first generation. The system consisted of local networks, multi-functional field control stations, enhanced operation stations, main computers, system management stations, and inter-network connectors. The core feature was that it used a local network as the system backbone, with each unit as a network node; network protocols gradually unified with MAP standards or were compatible with MAP, improving data communication capabilities and moving towards standardization; product design became standardized, modular, and structured; control functions were improved, and the user interface was user-friendly; management functions were decentralized, significantly enhancing system reliability, adaptability, and expansion flexibility. [6]
Mid-1980s to late 1980s (Third Generation)
Representative products included MAX’s MAX-1000+PLUS, Siemens’ Teleperm-XP, Bailey’s INFI-90, Westinghouse’s WDPF II, and ABB’s Procontrol-P. The development background was to overcome the inconvenience of proprietary local network interconnection in the second generation products and meet higher requirements for production process automation. The support from computer companies’ technical services also promoted changes in industrial division of labor. Core features included: enhanced information management functions, capable of high-level information management systems; adopting standard communication network protocols to achieve open system communication and solve the problem of interconnection between different devices; applying 32-bit microprocessors and intelligent I/O to improve system performance and control strategies; operation stations introduced technologies such as three-dimensional graphics display, making operation more convenient; hardware used specialized integrated circuits and surface mount technology, improving reliability; supporting personal computers and programmable controllers for access, enhancing system composition flexibility; process control configuration used CAD methods and introduced expert systems to achieve self-tuning, self-diagnosis, and other functions. [6]
Since the 1990s (Fourth Generation)
Marked by Honeywell’s Experion PKS, Emerson’s PlantWeb, Foxboro’s A2, Yokogawa’s R3, and ABB’s IndustrialIT system, the core feature was information (information) and integration (integration). The system architecture is divided into four layers: the enterprise management layer, the factory (workshop) layer, the unit (unit group) monitoring layer, and the field control instrument layer. The main features include: enhanced informatization, possessing comprehensive SCADA functions, equipment management and intelligent maintenance functions, and energy management functions; integration, achieving functional and product integration, using third-party product integration or OEM methods; blurred control object division, supporting mixed control of process, logic, and batch processing, using IEC61131-3 standard configuration; further decentralization, integrating fieldbus technology, installing I/O modules on-site, and changing the communication between the control station and I/O to a field serial bus; system openness, supporting third-party product connections at the enterprise management, factory (workshop), and unit (unit group) monitoring levels; service specialization, manufacturers focusing on industry solution design and implementation, providing specialized solutions and services.

System Name
The term “distributed control system” was derived by translating the product names of foreign companies. Due to the numerous manufacturers and varying system designs, each system has its own unique features in terms of functions and characteristics. Therefore, the naming of the products also varies. In China, there are different names used during translation, the most common ones being distributed control system (distributed control system, DCS), total distributed control system (total distributed control system, TDCS), and distributed computer control system (distributed computer control system, DCCS). [6]
The differences in names merely reflect the differences in naming intentions and translation, while the essence of the system remains the same and the underlying meaning is consistent. The Chinese power industry commonly refers to it as a distributed control system. [6]
System Interpretation
DCS typically adopts a hierarchical structure, with each level consisting of several subsystems. Each subsystem achieves specific limited goals, forming a pyramid structure. Reliability is the lifeblood of DCS development, and to ensure high reliability of DCS, there are three main measures: first, widely applying highly reliable hardware equipment and production processes; second, widely adopting redundancy technology; third, extensively implementing fault-tolerant technology, self-diagnosis, and automatic processing techniques in software design. Currently, the MTBF of most distributed control systems can reach tens of thousands or even hundreds of thousands of hours.
A distributed control system is a system with multiple physical and logical resources (multiple computers or processing units, multiple data sources, multiple instruction sources and programs) distributed, using a certain network or communication network for resource interconnection, with high local resource autonomy ability, mutual cooperation ability among resources, and overall coordination and control ability of resources. It can achieve dynamic management and allocation of distributed resources, parallel operation of distributed programs, and computer network control systems with decentralized functions. The meaning of the distributed control system mainly focuses on “dispersion”, and the meaning of “dispersion” includes several aspects. [6]
Dispersed Configuration
The geographical locations of each controlled device are dispersed, and the corresponding system control equipment is also configured in a dispersed manner. Multiple microprocessor-based distributed control units respectively undertake different control tasks. [6]
Function Dispersion
The functions of the distributed control system are not concentrated in the central control unit. Instead, they are distributed among various dispersed control units; moreover, the data acquisition, process control, operation display, monitoring operation, self-tuning, etc. of the control system are also decentralized and relatively independent. [6]
Display Dispersion
The display function of the distributed control system can not only be concentratedly presented on the central operation station, but also be dispersed to local operation stations. The central operation station has the ability to display all information of any dispersed process point in the entire system, and can be displayed on different display terminals; the local operation station can not only display on-site information through the on-site control unit at any time, but also the third and fourth generation distributed control systems can call information from other local operation stations or the central operation station at any local operation station for decentralized display. [6]
Database Dispersion
Modern distributed control systems mostly adopt distributed database systems, with local databases set up in the field control units and control stations, and shared by the entire system. [6]
Communication Dispersion
The distributed control system adopts local network communication technology. Each process unit in the network has equal communication control rights and can achieve decentralized communication. [6]
Power Supply Dispersion
The distributed control system provides independent power supply devices for different control units, enabling the distribution of system power supply and improving the reliability of the system. [6]
Load Dispersion In the distributed control system, the overall tasks are reasonably distributed to each control unit. One control unit only assumes the control tasks of several local control loops or subsystems. The workload of the entire system is distributed, and the load of each control unit is basically uniform. [6]
Distributed Hazards
“The implementation of ‘distributing'” means that the hazards of the entire system are distributed.

Open-loop Control
The open-loop control of discrete quantities is the most basic control function of PLC. The instruction system of PLC has strong logical operation capabilities, which can easily realize various logical control methods such as timing, counting, and sequential (stepwise) control. Most PLCs are used to replace traditional relay contactor control systems. [9]
Closed-loop Control of Analog Quantities
For closed-loop control systems of analog quantities, in addition to having discrete input and output points, there also need to be analog input and output points to sample the input and adjust the output to achieve continuous regulation and control of parameters such as temperature, flow, pressure, displacement, and speed. Currently, PLCs not only have this function in large and medium-sized machines, but also some small machines also have this function. [9]
Digital Quantity Control
When the control system has rotary encoders and pulse servo devices (such as stepper motors), PLC can be used to realize the function of receiving and outputting high-speed pulses, achieving digital quantity control. More advanced PLCs have specially developed digital control modules, which can realize curve interpolation functions. Recently, new motion unit modules have also been launched, which can provide digital quantity control technology programming languages, making PLC digital quantity control more simple. [9]
Data Acquisition and Monitoring
Since PLCs are mainly used for on-site control, collecting on-site data is a necessary function. On this basis, connecting PLCs with upper computers or touch screens can not only observe the current values of these data but also conduct timely statistical analysis. Some PLCs have data recording units, which can use the storage card of a general personal computer to insert into this unit to save the collected data. Another feature of PLCs is that they have many self-checking signals. By taking advantage of this feature, PLC control systems can achieve self-diagnostic monitoring, reducing system failures and improving system reliability. [9]
PLC Applications in Intelligent Manufacturing
In the field of intelligent manufacturing, through real-time data analysis, intelligent PLC systems can automatically adjust operating parameters to adapt to changing production needs and environmental conditions. This not only speeds up the production process but also improves product quality and system stability. The application framework is as follows. [11]
Process Control Layer: This layer is the core of PLC and is responsible for direct control of the production process. It completes the functions of data acquisition, real-time storage, processing, and transmission of process variables. The human-machine interface should not be directly connected to the process control layer.
Operation Monitoring Layer: This layer is the main human-machine interface of PLC and is responsible for processing and storing data from the process control layer and achieving centralized operation management functions. The equipment of the operation monitoring layer should not directly have process interface units, and process variables should not be connected to PLC through the operation monitoring layer equipment.
Data Service Layer: This layer is the intermediate layer for data exchange between the internal network of PLC and the external network, used to provide data services to users indirectly involved in the production process. The data service layer should exchange data with the process control layer and operation monitoring layer through proxy servers or industrial-grade firewalls, and should not directly establish data communication. Data services related to production operations or system management (such as alarms, historical records, diagnostics, etc.) should not be implemented in the data service layer.

There are a wide variety of PLC products. The different models of PLC correspond to various structural forms, performance, capacity, instruction systems, programming methods, and prices, and they are also suitable for different application scenarios. Therefore, choosing the appropriate PLC is of great significance for improving the technical and economic indicators of the PLC control system. [5]
PLC Model
The selection of PLC should mainly be based on comprehensive consideration of factors such as PLC model, capacity, I/O module, power module, special function module, communication networking capability, etc. The basic principle for selecting PLC model is to strive for the best performance-price ratio while meeting functional requirements and ensuring reliability and ease of maintenance. When choosing, the main factors to consider include reasonable structural type, installation method, corresponding functional requirements, response speed requirements, system reliability requirements, and the uniformity of model, etc. [5]
Structural types
PLC mainly has two structural types: integrated type and modular type. [5]
The average price of each I/O point in an integrated PLC is lower than that of a modular PLC, and it is relatively smaller in size. It is generally used in small control systems where the process of the system is relatively fixed. On the other hand, modular PLC offers flexible and convenient functionality expansion. It has a wide range of options in terms of I/O points, the ratio of input points to output points, and types of I/O modules, and is also easy to maintain. It is generally used in more complex control systems. [5]
Installation method
The installation methods of PLC systems can be categorized as centralized, remote I/O type, and distributed in a networked manner involving multiple PLCs. [5]
Centralized mode does not require setting up drivers for remote I/O hardware, and it has fast system response and low cost. Remote I/O mode is suitable for large systems where the devices are widely distributed. Remote I/O can be installed separately near the field devices, with short connections, but additional drivers and remote I/O power supplies are needed. Distributed mode with multiple PLCs connected is suitable for situations where multiple devices need to be independently controlled while also being interconnected. Small PLCs can be selected, but a communication module must be added. [5]
Functional Requirements
Most small-sized (low-end) PLCs have functions such as logical operations, timing, and counting. They can meet the control requirements for equipment that only requires switch quantity control. [5]
For systems that mainly use on-off control with a small amount of analog control, an enhanced low-end PLC with A/D and D/A conversion units, as well as addition and subtraction arithmetic operations and data transmission functions, can be selected. For systems with more complex control requirements, such as implementing PID calculations, closed-loop control, and communication networking functions, depending on the size and complexity of the control, medium or high-end PLCs can be chosen. However, medium and high-end PLCs are more expensive and are generally used in large-scale process control and distributed control systems and other scenarios. [5]
Response speed
PLC is a general-purpose controller designed for industrial automation. The response speed of different grades of PLCs generally can meet the requirements within their application scope. If PLCs are to be used across different ranges, or if certain functions or signals have special speed requirements, then the response speed of the PLC should be carefully considered. One can choose PLCs with high-speed I/O processing capabilities, or PLCs with fast response modules and interrupt input modules, etc. [5]
Reliability
The reliability of general system PLCs can all meet the requirements. For systems with extremely high reliability demands, it is necessary to consider whether to adopt a redundant system or a hot standby system. [5]
Uniformize the model of the equipment
For an enterprise, it is advisable to ensure the uniformity of PLC models. The main considerations include the following three aspects: [5]
1) Uniform model allows the modules to serve as backups for each other, facilitating the procurement and management of spare parts. [5]
2) The models are uniform, and their functions and usage methods are similar, which is conducive to the training of technical personnel and the improvement of technical proficiency. [5]
3) The models are uniform, their external devices are common, resources can be shared, it is easy to connect and communicate, and when equipped with a host computer, it is easy to form a multi-level distributed control system.

When designing a programmable logic controller system, the first step is to determine the control scheme. The next step is to select the programmable logic controller for the engineering design. The characteristics of the process flow and application requirements are the main basis for design selection. The programmable logic controller and related equipment should be integrated and standardized. The selection should be based on the principle of facilitating integration with industrial control systems and easy expansion of its functions. The selected programmable logic controller should be a mature and reliable system with operational performance in the relevant industrial field. The system hardware, software configuration and functions of the programmable logic controller should be adapted to the scale of the device and control requirements. Being familiar with programmable logic controllers, function block diagrams and related programming languages is beneficial for shortening the programming time. Therefore, during engineering design selection and estimation, detailed analysis of the characteristics of the process flow, control requirements, clear control tasks and scopes, and determination of required operations and actions should be conducted. Then, based on the control requirements, estimate the input and output points, required memory capacity, determine the functions of the programmable logic controller, and the characteristics of external devices, etc. Finally, select a programmable logic controller with a higher performance-to-price ratio and design the corresponding control system. [5]
Point count estimation
When estimating I/O points, an appropriate margin should be considered. Usually, based on the statistically calculated input and output points, an additional 10% to 20% of expandable margin is added as the estimated data for input and output points. During actual ordering, the input and output points need to be rounded according to the product characteristics of the programmable logic controller of the manufacturer. [5]
Memory capacity
Memory capacity refers to the size of the hardware storage units provided by the programmable controller itself. Program capacity refers to the size of the storage units used by the user’s application programs in the memory. Therefore, program capacity is smaller than memory capacity. During the design stage, since the user’s application programs have not yet been compiled, the program capacity is unknown at this stage and can only be known after the program debugging. To enable a certain estimation of program capacity during the design selection process, the memory capacity estimation is usually adopted as a substitute. [5]
There is no fixed formula for estimating the memory capacity. Many literature sources provide different formulas. Generally, they are based on multiplying the number of digital I/O points by 10 to 15, and adding 100 times the number of analog I/O points. This number is taken as the total number of memory words (16 bits as one word), and an additional 25% is considered as a reserve. [5]
Control function selection
This selection includes the options for arithmetic functions, control functions, communication functions, programming functions, diagnostic functions, and processing speed, etc. [5]
1. Computing Function
The computing functions of simple programmable logic controllers include logical operations, timing and counting functions; the computing functions of ordinary programmable logic controllers also include data shifting, comparison and other computing functions; more complex computing functions include algebraic operations, data transmission, etc.; in large programmable logic controllers, there are also analog PID computing and other advanced computing functions. With the emergence of open systems, communication functions have been available in programmable logic controllers. Some products have communication with lower-level machines, some have communication with peer-level machines or upper-level machines, and some have the function of data communication with factories or enterprise networks. When selecting and designing, it should be based on the actual application requirements and reasonably choose the required computing functions. In most application scenarios, only logical operations and timing/counting functions are needed; some applications require data transmission and comparison; when used for analog quantity detection and control, algebraic operations, numerical conversion and PID operations, etc. are used. When displaying data, decoding and encoding operations are also required. [5]
2. Control Function
The control functions include PID control calculation, feedforward compensation control calculation, ratio control calculation, etc. These should be determined according to the control requirements. The programmable logic controller is mainly used for sequential logic control. Therefore, in most cases, single-loop or multi-loop controllers are commonly used to solve the control of analog quantities. Sometimes, dedicated intelligent input/output units are used to complete the required control functions, thereby improving the processing speed of the programmable logic controller and saving memory capacity. For example, PID control units, high-speed counters, analog units with speed compensation, ASC code conversion units, etc. are adopted. [5]
3. Communication Function
The medium and large-sized programmable logic controller systems should support various field buses and standard communication protocols (such as TCP/IP), and when necessary, they should be able to connect to the factory management network (TCP/IP). The communication protocols should comply with ISO/IEEE communication standards and should be open communication networks. [5]
The communication interfaces of the programmable logic controller system should include serial and parallel communication interfaces, RIO communication ports, common DCS interfaces, etc. For large and medium-sized programmable logic controllers, the communication bus (including interface devices and cables) should be configured in a 1:1 redundant manner. The communication bus should comply with international standards, and the communication distance should meet the actual requirements of the device. [5]
In the communication network of a programmable logic controller system, the communication rate of the upper-level network should be greater than 1 Mbps, and the communication load should not exceed 60%. The main forms of the communication network of the programmable logic controller system are as follows: [5]
1) The PC serves as the master station, and multiple programmable logic controllers of the same model serve as slave stations, forming a simple programmable logic controller network; [5]
2) One programmable logic controller serves as the master station, while other programmable logic controllers of the same model act as slave stations, forming a master-slave programmable logic controller network. [5]
3) The programmable logic controller network is connected to the large DCS through a specific network interface and serves as a sub-network of the DCS. [5]
4) Specialized Programmable Logic Controller Network (communication network for each manufacturer’s specialized programmable logic controller). [5]
To reduce the CPU’s communication workload, based on the actual requirements of the network configuration, communication processors with different communication functions (such as point-to-point and fieldbus) should be selected. [5]
4. Programming Function
Offline Programming Mode: The programmable logic controller and the programmer share one CPU. When the programmer is in programming mode, the CPU only provides services for the programmer and does not control the on-site equipment. After the programming is completed, the programmer switches to the operation mode, and the CPU controls the on-site equipment. It cannot perform programming. Offline programming mode can reduce system costs, but it is inconvenient for use and debugging. Online Programming Mode: The CPU and the programmer have their own CPUs. The host CPU is responsible for on-site control and exchanges data with the programmer within one scanning cycle. The programmer sends the online-programmed programs or data to the host, and in the next scanning cycle, the host runs according to the newly received programs. This method is costly, but it is convenient for system debugging and operation. It is often adopted in medium and large programmable logic controllers. [5]
Five standardized programming languages: Sequential Function Chart (SFC), Ladder Diagram (LD), Function Block Diagram (FBD), three graphical languages, and Instruction List (IL), Structured Text (ST), two text-based languages. The programming language selected should comply with its standards (IEC 61131-23), and at the same time, it should support various programming forms such as C, Basic, etc., to meet the control requirements of special control scenarios. [5]
5. Diagnostic Function
The diagnostic function of the programmable logic controller includes both hardware and software diagnostics. Hardware diagnostics determine the location of hardware faults through logical judgments of the hardware. Software diagnostics are divided into internal diagnostics and external diagnostics. Internal diagnostics involve diagnosing the performance and functions of the PLC through software. External diagnostics involve diagnosing the information exchange functions between the CPU of the programmable logic controller and external input/output components through software. [5]
The strength of the diagnostic function of a programmable logic controller directly affects the technical requirements for operators and maintenance personnel, as well as the average maintenance time. [5]
6. Processing Speed
The programmable logic controller operates in a scanning mode. From the perspective of real-time requirements, the processing speed should be as fast as possible. If the duration of a signal is shorter than the scanning time, the programmable logic controller will fail to scan this signal, resulting in the loss of signal data. [5]
The processing speed is related to the length of the user program, the CPU processing speed, and the quality of the software. The response speed of the programmable logic controller contacts is fast and high. The execution time of each binary instruction is approximately 0.2 to 0.4 seconds. Therefore, it can meet the requirements of high control and fast response in applications. The scan cycle (processor scan cycle) should meet the following conditions: the scan time of a small programmable logic controller is no more than 0.5 ms/K; the scan time of a medium-sized programmable logic controller is no more than 0.2 ms/K. [5]
Controller types
Programmable logic controllers are classified into two types based on their structure: integrated type and modular type. They are further categorized by application environment into field installation and control room installation types. According to the CPU word length, they are divided into 1-bit, 4-bit, 8-bit, 16-bit, 32-bit, 64-bit, etc. From an application perspective, selection is typically based on control functions or the number of input/output points. [5]
The I/O points of the integrated programmable logic controller are fixed, so users have limited choices and it is suitable for small-scale control systems. The modular programmable logic controller provides various I/O cards or modules, allowing users to reasonably select and configure the I/O points of the control system. The function expansion is convenient and flexible, and it is generally used in medium and large-scale control systems. [5]
Input and output types
Switching quantities mainly refer to input quantities and output quantities, which refer to the auxiliary points of a device. For example, the relay auxiliary points of the temperature controller of a transformer (the relay changes state when the transformer overheats), the auxiliary points of the valve cam switch (the relay changes state after the valve is switched), the auxiliary points of the contactor (the relay changes state after the contactor operates), the thermal relay (the relay changes state after the thermal relay operates), these points are generally transmitted to the PLC or integrated protection device. The power is generally provided by the PLC or integrated protection device, and they do not have their own power supply, so they are called passive contacts or PLC or integrated protection device’s input quantities. [5]
1. Digital quantity
A physical quantity that is discrete both in time and quantity is called a digital quantity. The signal representing the digital quantity is called a digital signal. The electronic circuits operating under digital signals are called digital circuits. [5]
For example: When using electronic circuits to record the number of parts output from an automatic production line, each time a part is sent out, an electronic circuit receives a signal, which is 1. While there is no part being sent out, the signal given to the electronic circuit is 0. This is for counting. It can be seen that this signal for the number of parts is discontinuous both in time and quantity. Therefore, it is a digital signal. The smallest unit of quantity is 1 part. [5]
2. Analog Quantity
A physical quantity that is continuous in both time and value is called an analog quantity. The signal representing an analog quantity is called an analog signal. The electronic circuits operating under analog signals are called analog circuits. [5]
For example: The voltage signal output by a thermocouple during operation belongs to an analog signal. This is because the measured temperature will not experience sudden jumps under any circumstances. Therefore, the voltage signal measured is continuous both in time and in quantity. Moreover, any value of this voltage signal during its continuous change process represents a specific physical meaning, that is, it indicates a corresponding temperature. [5]
Conversion Principle
1. A digital-to-analog converter is a system that converts digital signals into analog signals. Generally, a low-pass filter can achieve this. The digital signal is first decoded, that is, the digital code is converted into the corresponding level, forming a stepped signal, and then a low-pass filter is applied. [5]
According to the theory of signals and systems, a digital step-like signal can be regarded as the convolution of an ideal impulse sampling signal and a rectangular pulse signal. Then, by applying the convolution theorem, the frequency spectrum of the digital signal is the product of the frequency spectrum of the impulse sampling signal and the frequency spectrum of the rectangular pulse (i.e., the Sa function). Thus, by using the reciprocal of the Sa function as the spectral characteristic compensation, the digital signal can be restored to the sampling signal. According to the sampling theorem, the frequency spectrum of the sampling signal, after being filtered by an ideal low-pass filter, results in the frequency spectrum of the original analog signal. [5]
In general, these principles are not directly applied because sharp sampling signals are difficult to obtain. Therefore, these two filters (the Sa function and the ideal low-pass filter) can be combined (cascaded), and since the filtering characteristics of these systems are physically impossible to achieve, they can only be approximated in the actual system. [5]
2. The analog-to-digital converter is a system that converts analog signals into digital signals, involving a process of filtering, sampling, holding and encoding. [5]
The analog signal is filtered by a band-pass filter, sampled and held by a circuit, and then transformed into a stepped-shaped signal. Subsequently, it passes through an encoder, converting each level of the stepped signal into a binary code.

(1) High reliability. Since most PLCs use single-chip microcomputers, they have high integration. Coupled with the corresponding protection circuits and self-diagnosis functions, the reliability of the system is enhanced. [8]
(2) Easy programming. PLC programming mostly adopts relay control ladder diagrams and command statements. The number of these is much less than that of microcomputer instructions. Except for mid-to-high-end PLCs, the small-sized PLCs usually have only about 16 lines. Due to the graphic and simple nature of the ladder diagram, it is easy to master and use, and even without computer expertise, programming can be done. [8]
(3) Flexible configuration. Since PLCs adopt a modular structure, users only need to simply combine to flexibly change the functions and scale of the control system. Therefore, it can be applied to any control system. [8]
(4) Complete input/output function modules. One of the greatest advantages of PLC is that for different on-site signals (such as DC or AC, switch quantity, digital quantity or analog quantity, voltage or current, etc.), there are corresponding templates that can be directly connected to the devices in the industrial field (such as buttons, switches, current sensing transmitters, motor starters or control valves, etc.) and connected to the CPU mainboard through a bus. [8]
(5) Easy installation. Compared with computer systems, the installation of PLCs does not require a dedicated machine room or strict shielding measures. When using, simply connect the detection devices, actuators and the I/O interface terminals of PLC correctly, and it can work normally. [8]
(6) Fast operation speed. Since the control of PLC is executed by program, both its reliability and operation speed are incomparable to relay logic control. [8]
In recent years, the use of microprocessors, especially with the large-scale adoption of single-chip microcomputers, has greatly enhanced the capabilities of PLCs, and the difference between PLCs and microcomputer control systems has become smaller, especially for high-end PLCs.

When the programmable logic controller is put into operation, its working process is generally divided into three stages: input sampling, user program execution, and output refreshing. Completing these three stages is called one scan cycle. During the entire operation period, the CPU of the programmable logic controller repeats the execution of these three stages at a certain scanning speed. [5]
Input Sampling
During the input sampling stage, the programmable logic controller reads in all input states and data sequentially in a scanning manner and stores them in the corresponding units in the I/O image area. After the input sampling is completed, it proceeds to the user program execution and output refresh stage. During these two stages, even if the input states and data change, the states and data in the corresponding units of the I/O image area will not change. Therefore, if the input is a pulse signal, the width of this pulse signal must be greater than one scan cycle to ensure that the input can be read in under any circumstances. [5]
User program execution
During the execution of the user program, the programmable logic controller always scans the user program (ladder diagram) in a top-down sequence. When scanning each ladder diagram, it always first scans the control circuit composed of the contacts on the left side of the ladder diagram, and performs logical operations on the control circuit composed of the contacts in the order of left to right and top to bottom. Then, based on the result of the logical operation, it refreshes the state of the corresponding bit of the logic coil in the system RAM storage area; or refreshes the state of the corresponding bit of the output coil in the I/O image area; or determines whether to execute the special function instruction specified by the ladder diagram. [5]
That is, during the execution of the user program, only the states and data of the input points within the I/O image area will not change, while the states and data of other output points and software devices within the I/O image area or the system RAM storage area may change. Moreover, the program execution result of the top-level ladder diagram will affect all the ladder diagrams below that use these coils or data; conversely, the status or data of the refreshed logic coils in the lower-level ladder diagram can only take effect on the program above it in the next scanning cycle. [5]
During the execution of the program, if the immediate I/O instruction is used, the I/O points can be accessed directly. That is, if the I/O instruction is used, the value of the input process image register will not be updated. The program directly fetches the value from the I/O module, and the output process image register will be updated immediately. This is somewhat different from immediate input. [5]
Output Refresh
After the user program is scanned, the programmable logic controller enters the output refresh stage. During this period, the CPU refreshes all the output latch circuits according to the corresponding states and data in the I/O mapping area, and then drives the corresponding peripheral devices through the output circuit. This is the actual output of the programmable logic controller. [5]
Summary
Based on the description of the above process, the characteristics of the PLC working process can be summarized as follows: [7]
① The PLC adopts a centralized sampling and centralized output working mode, which reduces the influence of external interference. [5]
② The working process of PLC is a cyclic scanning process. The length of the scanning cycle depends on factors such as the execution speed of instructions and the length of the user program. [5]
③ The influence of output on input shows a lag phenomenon. The PLC adopts a centralized sampling and centralized output working mode. After the sampling stage is completed, the change in input status will not be received until the next sampling cycle. Therefore, the length of this lag time mainly depends on the length of the cycle. In addition, factors affecting the lag time also include the input filtering time and the lag time of the output circuit, etc. [5]
The content of the output image register depends on the result of the user program’s scanning execution. [5]
The content of the output latch is determined by the data in the output image register during the previous output refresh period. [5]
The current actual output status of the PLC is determined by the content of the output latch.

Origin
The development of production technology requirements in the American automotive industry led to the emergence of PLCs. In the 1960s, when General Motors of the United States was adjusting its factory production lines, they found that the relay and contactor control systems were difficult to modify, large in size, noisy, inconvenient to maintain, and had poor reliability. Therefore, they proposed the well-known “General Motors Ten Points” bidding indicators. [3]
In 1969, the American Digital Equipment Corporation developed the first programmable controller (PDP-14), which was tested on the production line of General Motors and achieved remarkable results. In 1971, Japan developed the first programmable controller (DCS-8); in 1973, Germany developed the first programmable controller; in 1974, China began to develop programmable controllers; in 1977, China promoted PLC in the industrial application field. [3]
02:38
The Lighthouse Country has won again! PLC originated in the United States. There’s no way to dispute it.
The original purpose was to replace mechanical switch devices (relay modules). However, since 1968, the functions of PLC have gradually replaced relay control boards. Modern PLCs have more functions. Its applications have expanded from single process control to the control and monitoring of the entire manufacturing system. [4]
Development
In the early 1970s, microprocessors emerged. Soon they were introduced into programmable logic controllers, which enabled these controllers to add functions such as computing, data transmission and processing, thus completing an industrial control device with true computer characteristics. At this time, the programmable logic controllers were the result of the combination of microcomputer technology and the conventional control concept of relays. After personal computers developed, to facilitate and reflect the functional characteristics of programmable controllers, the programmable logic controller was named Programmable Logic Controller (PLC). [5]
In the mid-to-late 1970s, programmable logic controllers entered the stage of practical application. Computer technology was fully integrated into programmable controllers, leading to a significant leap in their functionality. Higher computing speed, ultra-small size, more reliable industrial anti-interference design, analog quantity calculation, PID functions, and extremely high cost-effectiveness have established their position in modern industry. [5]
In the early 1980s, programmable logic controllers had been widely used in advanced industrial countries. The number of countries producing programmable logic controllers was increasing worldwide, and their production volume was rising as well. This indicated that programmable logic controllers had entered a mature stage. [5]
From the 1980s to the mid-1990s, it was the period when programmable logic controllers (PLCs) experienced the fastest growth, with an annual growth rate consistently remaining at 30% to 40%. During this period, the processing capabilities of PLCs for analog quantities, digital operations, human-machine interface, and network capabilities were significantly enhanced. PLCs gradually entered the field of process control and replaced the DCS systems that were dominant in process control applications. [5]
In the late 20th century, the development characteristics of programmable logic controllers were more adapted to the needs of modern industry. During this period, large-scale machines and ultra-small machines were developed, various special function units were born, various human-machine interface units and communication units were produced, making it easier to provide the necessary components for industrial control equipment that uses programmable logic controllers.

Touch screen (also known as “touch panel” or “touch control panel”) is an electronic display device that can receive input signals from touch points or other means. When a graphic button on the screen is touched, the tactile feedback system on the screen can be driven by the pre-programmed program to control various connected devices, replacing mechanical button panels and creating vivid audio-visual effects through the LCD display screen. [1]
Since the earliest resistive touch screens appeared in 1974, with the advancement of technology and the increasing demand for applications, various touch technologies have emerged to meet the needs of different industries and levels. Nowadays, commercialized touch screen technologies have been formed, including resistive technology touch screens, capacitive technology touch screens, infrared technology touch screens, surface acoustic wave (SAW) technology touch screens, etc., and have been widely applied in many fields such as mobile phones, tablet computers, retail, public information inquiries, multimedia information systems, medical equipment, industrial automatic control, entertainment and catering industries, automatic ticketing systems, and educational systems.