The seven basic characteristics of PLC
1 programming method is easy to learn
Ladder diagram is the most used plc programming language. Its circuit symbols and expressions are similar to relay circuit schematics. Ladder diagram language is intuitive and easy to understand. Electrical technicians familiar with relay circuit diagrams can spend only a few days. Become familiar with the ladder language and use it for programming user programs.
Ladder language is actually a user-oriented high-level language. When PLC executes a ladder program, it “translates” it into assembly language and executes it.
2. Strong function, high performance-price ratio
A small PLC has hundreds of user-programmable components inside it that can implement very complex control functions. Compared with the relay system with the same function, it has a high performance-cost ratio. PLC can also be networked through communications to achieve decentralized control and centralized management.
3 complete hardware, user-friendly and adaptable
PLC products have been standardized, serialized, modularized, equipped with a variety of hardware devices for users to choose from, the user can be flexible and convenient system configuration, the formation of different functions, different scales of the system. PLC installation wiring is also very convenient, generally use the terminal block to connect the external wiring. PLC has a strong load capacity, can directly drive the general solenoid valve and small and medium-sized AC contactor.
After the hardware configuration is determined, by modifying the user program, it is possible to easily and quickly adapt to changes in process conditions.
4. High reliability and strong anti-interference ability
The traditional relay control system uses a large number of intermediate relays and time relays. Poor contact due to poor contact. PLC replaces intermediate relays and time relays with software, leaving only a small number of hardware components related to input and output. The wiring can be reduced to one-tenth or even one-hundredth of the relay control system because of faulty contacts. Greatly reduced.
PLC uses a series of hardware and software anti-jamming measures, has a strong anti-jamming capability, the average time between failures of tens of thousands of hours or more, can be directly used in industrial production sites with strong interference, has been recognized as the most reliable industry One of the control devices.
5. System design, installation, commissioning less
The PLC software function replaces a large number of relays, time relays, and counters in the relay control system, which greatly reduces the design, installation, and wiring of the control cabinet.
PLC's ladder program can be designed using sequential control design. This programming method is very regular and easy to master. For a complex control system, if the correct design method is mastered, the design of the ladder diagram takes much less time than designing the relay system circuit diagram.
You can simulate and debug the PLC user program in the lab. The input signal is simulated with a small switch and the status of the output signal is observed through the LED on the PLC. After completing the installation and wiring of the system, the problems found during the on-site commissioning process can generally be resolved by modifying the program. The debugging time of the system is much less than that of the relay system.
6. Small maintenance workload and easy maintenance
PLC's failure rate is very low, and there is a perfect self-diagnosis function. When the PLC or an external input device and an actuator fail, the cause of the fault can be easily ascertained based on the information provided by the light emitting diode (LED) or the programming device on the PLC, and the fault can be promptly corrected by replacing the module.
7. Small size, low energy consumption
For a complex control system, the use of a PLC can 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. Therefore, the size of the switch cabinet can be reduced to 1/2 or even 1/1. 10.
The wiring of the PLC control system is much less than the wiring of the relay control system, so it can save a large number of wiring and accessories, reduce the number of installation wiring hours, plus the size of the switch cabinet, can save a lot of costs.
