In recent years, with the rapid development of technology, the application and development of PLCs in industrial automation control, including analog and digital signal processing and human-machine interfaces, have greatly improved. PLCs have gradually become the mainstream control equipment in China's automation control field, playing an increasingly important role in various areas of automation control. As a digital computing electronic system, PLCs are specifically designed for industrial environments, enabling industrial automation control at the standalone, workshop, and factory levels. Their strong anti-interference capabilities and ease of maintenance have led to their increasing importance in the field of industrial automation control. Furthermore, the extremely high reliability of PLCs in real-time monitoring at the control site, as well as their simple and flexible programming, have further contributed to their widespread application in industrial automation control.
1. The composition and functions of a PLC
1.1 PLC Composition
A PLC mainly consists of a power supply, CPU, interface circuits, I/O circuits, and memory. The power supply includes system power, power-down protection, and backup power. The CPU, or Central Processing Unit, performs logic and mathematical operations and coordinates the entire system's operation. Interface circuits refer to the channels connecting the PLC to field devices and peripherals. I/O circuits consist of input circuits that isolate and convert input signals, and output circuits that amplify and convert the PLC's output to drive field devices. The memory primarily stores system logic variables, user programs, monitoring data, and other information.
1.2 PLC Functions
The functional analysis of a PLC can be mainly analyzed from three aspects: on/off control, time-limited and counting control, and step control and data processing.
Control of switching quantities. This main function, or advantage, refers to its ability to control the movement of mechanical components based on limit switches and operating buttons, combined with detection signals provided at the control site.
Time-limited and counting control. Time-limited control refers to the ability to set relevant timing indicators in a PLC system, with flexible and adaptable time settings. This is primarily used for accurate real-time control of the system. PLC counting control utilizes counters, which can be categorized into high-speed, ordinary, and reversible counters. Their function is to perform different counting control tasks within the system.
Stepping control and data processing. PLC stepping control is mainly accomplished using shift registers. PLC data processing can not only perform addition, subtraction, multiplication, division, exponentiation, and root extraction, but also compare, transfer, and shift data using logical operations such as OR, AND, XOR, and NOT.
2. Application of PLC in Automation Control
With the rapid development of society and science and technology, PLC technology has also become increasingly mature. Its current applications in my country's automation control can be analyzed from four main aspects: applications of switching quantity control, process and motion control, applications of analog quantity and centralized system control, and precautions for PLC industrial applications and anti-interference design. The following is a detailed discussion:
2.1 Switching control
The analysis of the application of PLC switching control in automation control can be mainly described from the following three aspects: ① In the current automation control applications in China, traditional relays are gradually being replaced by PLC switch control. PLC control effectively realizes logic and sequential control. Furthermore, PLC switches offer advantages such as simple wiring, high speed, convenient operation and maintenance, and high reliability. ② The application of PLC switches significantly improves system quality and greatly enhances and saves time and manpower. ③ This type of PLC switching control is now used not only for controlling single automated equipment but also for controlling multi-machine automated production lines. Typical applications include combination machine tools, injection molding machines, and packaging production lines.
2.2 Process and Motion Control
This article's analysis of PLC process and motion control mainly refers to process control and motion control. The following is a detailed analysis and discussion:
PLCs are mainly used for discrete process control and continuous process control. Specifically, process control is the process of working with the analog quantities of the system. This involves comparing and analyzing current analog quantities such as continuously changing pressure, current, voltage, and temperature with historical data to generate the switching quantities required by the user, so that the system parameters operate according to the requirements. This type of PLC is mainly used in chemical, metallurgical, and heat treatment industries in my country.
Furthermore, in motion control, PLCs primarily refer to their ability to control circular and linear motion. This control is achieved through pulse control of the system, resulting in extremely small displacements and thus very high control precision. This type of PLC motion control is currently mainly used in machinery, elevators, machine tools, and robotics in my country.
2.3 Analog Quantities and Centralized System Control
PLC analog control. PLCs not only control the system process, but also enable instrument monitoring of the system through control statements, thus effectively improving the accuracy of the control system. This is of great significance for the control of heat treatment heating, holding, and cooling processes in automation control.
Centralized control of PLC systems. In addition to achieving automated control, PLCs can also perform system self-control, such as fault detection and display. Furthermore, in automated control systems, there are logical relationships between I/O signals and intermediate memory units. This means that when a device malfunctions, these logical relationships are disrupted, allowing for the use of programmed fault diagnosis, fault analysis, and alarm control.
2.4. Precautions and Anti-interference Design for PLC Industrial Applications
To ensure the rational, safe, and stable application of PLCs in industrial settings, it is essential to pay attention to the precautions during application and the anti-interference design. The following is a detailed analysis of these two aspects:
Precautions for PLC Applications. In current automated control applications in my country, the following points should be noted regarding PLCs: Temperature: The ambient temperature should be between 0℃ and 55℃, and direct sunlight should be avoided; Air Humidity: The air humidity should be kept below 85%, and condensation should be prevented to ensure the PLC's insulation; Vibration: Continuous or frequent vibration between 10Hz and 55Hz is prohibited, and appropriate vibration damping material should be used; Air: The air surrounding the PLC should be protected from corrosive gases such as hydrogen chloride and hydrogen sulfide. If the air quality is unsuitable, air purification equipment should be installed.
Interference suppression design. When designing for interference suppression, the selection of PLC equipment should prioritize devices with strong anti-interference capabilities to ensure the normal operation of the PLC system. Furthermore, during the PLC interference suppression design process, the anti-interference capabilities should be tailored to the different functions of the PLC. For example, cable laying can generate electromagnetic interference, so different signals should be laid in layers to reduce electromagnetic interference.
