About PLC

September 26,2024

I. Brief Description

Over the years, Programmable Logic Controllers (hereinafter referred to as PLCs) have made a significant leap from wiring logic to stored logic; their functions have evolved from basic to advanced, achieving progress from logic control to digital control; their application fields have expanded from small to large, accomplishing a leap from simple control of individual equipment to handling various tasks such as motion control, process control, and distributed control. Today’s PLCs have significantly improved in their capabilities to process analog signals, digital computations, human-machine interfaces, and networking, becoming the mainstream control equipment in the industrial control field and playing an increasingly important role in various industries.

II. Applications of PLC

Currently, PLCs have been widely used in various industries both domestically and internationally, such as steel, oil, chemical, power, building materials, machinery manufacturing, automotive, light industry, textile, transportation, environmental protection, and cultural entertainment. The usage can be mainly categorized as follows:

Switching Logic Control
Replacing traditional relay circuits to achieve logic control and sequence control, PLCs can be used for controlling single equipment as well as multi-machine group control and automated assembly lines. Examples include injection molding machines, printing machines, bookbinding machines, modular machines, grinding machines, packaging production lines, and electroplating assembly lines.

Industrial Process Control
In industrial production processes, there are continuous variables such as temperature, pressure, flow rate, liquid level, and speed (i.e., analog signals). PLCs use corresponding A/D and D/A conversion modules and various control algorithm programs to process analog signals and complete closed-loop control. PID regulation is a commonly used method in general closed-loop control systems. Process control is widely applied in metallurgy, chemical, heat treatment, boiler control, and other fields.

Motion Control
PLCs can be used for controlling circular or linear motion. Generally, specialized motion control modules are used, such as single-axis or multi-axis position control modules that can drive stepper motors or servo motors, which are widely used in various machinery, machine tools, robots, elevators, and other applications.

Data Processing
PLCs are capable of mathematical operations (including matrix operations, function operations, logical operations), data transmission, data conversion, sorting, table lookup, bit manipulation, and can complete data collection, analysis, and processing. Data processing is generally used in large-scale control systems in industries such as papermaking, metallurgy, and food industry.

Communication and Networking

PLC communication includes communication between PLCs and communication between PLCs and other intelligent devices. With the development of factory automation networks, modern PLCs all have communication interfaces, making communication very convenient.

Features of PLC Applications

High Reliability and Strong Anti-Interference Ability
High reliability is a key performance indicator for electrical control equipment. PLCs, manufactured using modern large-scale integrated circuit technology and strict production processes, incorporate advanced anti-interference techniques in their internal circuits, resulting in high reliability. When using PLCs to construct control systems, the electrical wiring and switch contacts are reduced to a fraction of a hundred or even a thousand compared to equivalent relay contactor systems, thus significantly reducing faults. Additionally, PLCs have a hardware fault self-detection feature that can issue alarm messages in case of a fault. In the application software, users can also program self-diagnostic routines for peripheral devices, providing fault self-diagnosis protection for circuits and equipment outside the PLC. This ensures the entire system has extremely high reliability.

Complete Range of Accessories, Comprehensive Functions, and Strong Applicability
PLCs have evolved to offer a variety of scaled series products suitable for various industrial control scenarios. In addition to logic processing capabilities, most PLCs have comprehensive data processing abilities and can be used in a wide range of digital control fields. The emergence of a variety of functional units has allowed PLCs to permeate various industrial controls such as position control, temperature control, CNC, etc. With the enhancement of PLC communication capabilities and the development of human-machine interface technology, it has become very easy to use PLCs to form various control systems.

Easy to Learn and Use, Popular Among Engineering Technicians
PLCs are designed for industrial and mining enterprises as industrial control equipment. They have user-friendly interfaces and programming languages that are easily accepted by engineering technicians. The graphical symbols and expression methods of ladder diagram language are quite similar to those of relay circuit diagrams, opening the door to industrial control for people who are not familiar with electronic circuits or computer principles and assembly languages.

System Design Requires Less Work, Easy Maintenance, and Easy to Modify
PLCs use stored logic to replace wiring logic, greatly reducing the external wiring of control equipment. This shortens the design and construction cycle of control systems and makes daily maintenance easier. More importantly, it makes it possible to change the production process by altering the program of the same equipment. This is particularly suitable for production scenarios with multiple varieties and small batch sizes.

About PLC

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