Simply put, a PLC is equivalent to a collection of multiple conventional relays, time relays, and counters. It's easy to use, small in size, and its program can be modified as needed, saving the trouble of rewiring! PLCs were originally designed for applications requiring frequent changes to control circuits. Compared to relay circuits, PLCs have the following advantages:
1. High functionality and high performance-price ratio
A small PLC contains hundreds or even thousands of programmable elements, offering powerful functionality and the ability to implement highly complex control functions. Compared to relays with similar capabilities, it boasts a significantly higher performance-to-price ratio. Furthermore, programmable controllers can be networked for distributed control and centralized management.
2. The hardware is complete, user-friendly, and highly adaptable.
Programmable logic controllers (PLCs) are standardized, serialized, and modularized, offering a complete range of hardware options for users. Users can flexibly and conveniently configure systems to create systems of varying functions and scales. Installation and wiring of PLCs are also convenient, typically using terminal blocks for external connections. PLCs have strong load-carrying capacity and can directly drive common solenoid valves and AC contactors.
3. High reliability and strong anti-interference ability
Traditional relay control systems use a large number of intermediate relays and time relays. Due to poor contact, they are prone to failure. PLCs replace a large number of intermediate relays and time relays with software, leaving only a small amount of hardware related to input and output. Wiring can be reduced by 1/10 to 1/100 of the relay control system, and failures caused by poor contact are greatly reduced.
The PLC employs a series of hardware and software anti-interference measures, giving it strong anti-interference capabilities. Its mean time between failures (MTBF) reaches tens of thousands of hours or more, making it suitable for use in industrial production environments with strong interference. PLCs are widely recognized by users as one of the most reliable industrial control devices.
4. The system requires less design, installation, and debugging work.
PLCs replace a large number of intermediate relays, time relays, counters, and other devices in relay control systems with software functions, greatly reducing the workload of control cabinet design, installation, and wiring.
PLC ladder logic programs generally employ sequential control design methods. This programming method is highly systematic and easy to master. For complex control systems, ladder logic design takes significantly less time than designing relay system circuit diagrams.
The PLC user program can be simulated and debugged in the laboratory. Input signals are simulated using small switches, and the status of the output signals can be observed through LEDs on the PLC. After the system installation and wiring are completed, problems found during on-site commissioning can generally be resolved by modifying the program. The system's debugging time is much shorter than that of a relay system.
5. Simple programming method
Ladder diagrams are the most widely used programming language for programmable logic controllers (PLCs). Their circuit symbols and representations are similar to those of relay circuit diagrams. Ladder diagrams are visually intuitive, easy to learn and understand. Electrical technicians familiar with relay circuit diagrams can become familiar with ladder diagrams in just a few days and use them to write user programs.
Ladder diagram language is actually a user-oriented high-level language. When a programmable logic controller (PLC) executes a ladder diagram program, it uses an interpreter to "translate" it into assembly language before execution.
6. Minimal maintenance workload and easy repair.
PLCs have a very low failure rate and comprehensive self-diagnostic and display functions. When a PLC, external input device, or actuator malfunctions, the cause of the fault can be quickly identified based on the LEDs on the PLC or the information provided by the programmer. The fault can be quickly resolved by replacing the module.
7. Small size and low energy consumption
For complex control systems, using a PLC can significantly reduce the number of intermediate and time relays. A small PLC is roughly the size of several relays, thus reducing the size of the switchgear to 1/2 to 1/10 of its original size. www.diangon.com
PLC wiring is far less than that of relay control systems, thus saving a significant amount of wiring and accessories, reducing installation and wiring time, and consequently reducing costs. It's hard work to learn, but comfortable to do.
8. Adapting to changing times, enabling network communication
PLCs can be networked with computers and smart instruments to achieve distributed control and centralized management. They can also display the current working status and workflow of mechanical equipment, greatly facilitating production management and on-site maintenance.
9. Enhance product technology content and improve product image.
For complex mechanical equipment, using traditional relay control not only increases the difficulty of configuring the control box, but also makes the end customer feel that the product is not advanced enough. PLC-controlled machinery has better quality assurance. At the same time, using PLC increases the difficulty for competitors to imitate!
10. It is very convenient for future mechanical upgrades.
For complex mechanical equipment, if it can no longer meet the needs of use over time, it is necessary to upgrade and modify the equipment. If it is controlled by traditional relays, it will be very troublesome, and the old control box will basically have to be scrapped. However, it is very convenient to control with PLC. It only requires expanding a related I/O point and modifying the relevant control program.
