1. Programming method is easy to learn
The ladder diagram is the programming language of the most used PLC. Its circuit symbol and expression are similar to the relay circuit schematic. The ladder language is intuitive and easy to learn. The electrical technicians familiar with the relay circuit diagram can take only a few days. Familiar with the ladder language and used to program the user program of the digital control system.
2. Strong function, high performance and price ratio
There are thousands of user-programmable components in a PLC that enable very complex control functions. Compared with the same function of the relay system, it has a high performance-price ratio. PLC can realize distributed control and centralized management through communication networking.
3. Complete hardware support, user-friendly, adaptable
PLC products have been standardized, serialized and modularized. They are equipped with a wide range of hardware devices for users to choose. Users can configure the system flexibly and conveniently to form systems with different functions and different scales. PLC installation wiring is also very convenient, generally use terminal blocks to connect external wiring. PLC has a strong load capacity and can directly drive most solenoid valves and small and medium AC contactors.
After the hardware configuration is determined, by modifying the user program, it is convenient and quick to adapt to changes in process conditions.
4. High reliability and strong anti-interference ability
Traditional relay control systems use a large number of intermediate relay time relays. Due to poor contact of the contacts, it is prone to malfunction. The PLC replaces the intermediate relay and the time relay with software, leaving only a small number of hardware components related to the input and output, and the wiring can be reduced to less than one tenth of the relay control system, greatly reducing the malfunction caused by poor contact of the contacts.
PLC uses a series of hardware and software anti-interference measures, has strong anti-interference ability, and the average time between failures reaches tens of thousands of hours. It can be directly used in industrial production sites with strong interference. PLC is recognized by most users as the most reliable. One of the industrial control devices.
5. Less system design, installation and commissioning
PLC replaces a large number of intermediate relays, time relays, counters and other devices in the relay control system with software functions, which greatly reduces the design, installation and wiring of the control cabinet.
The ladder program of the PLC can be designed by the sequential control design method. This design method is very regular and easy to master. For complex control systems, the time to design a program in this way is much less than the time to design a relay system circuit diagram.
The simulation software PLCSIM can be used to simulate the function of the CPU module of the S7-300/400 and use it to debug the user program. In the on-site debugging process, the problems found can be solved by modifying the program. The debugging time of the system is much less than that of the relay system.
6. Small maintenance and convenient maintenance
The PLC has a low failure rate and a comprehensive fault diagnosis function. When the PLC or the external input device and the actuator fail, the information provided by the LED module on the signal module or the programming software can be used to quickly and easily find out the cause of the fault, and the method of replacing the module can quickly eliminate the fault.
7. Small size and low energy consumption
The complex control system uses PLC to reduce a large number of intermediate relays and time relays. The size of a small PLC is only equivalent to the size of several relays, so the size of the switch cabinet can be reduced to 1/2 to 1/10.
Compared with the relay control system, the PLC control system has a small amount of wiring, a short installation time, and a reduction in the size of the switch cabinet, so that a large amount of cost can be saved.