PLC is the reason for the rapid development, in addition to the objective needs of industrial automation, there are many unique advantages suitable for industrial control, it better solves the industrial control field generally concerned about the reliability, safety, flexibility, convenience and economy, etc., its main features are as follows.
1. Strong anti-interference ability, high reliability
In the traditional relay control system, the use of a large number of intermediate relays and time relays, due to the inherent shortcomings of the device, such as device aging, poor contact and contact jitter and other phenomena, greatly reducing the reliability of the system. In PLC control systems a large number of switching actions are accomplished by contactless semiconductor circuits, so failures are greatly reduced.
In addition, measures have been taken on the hardware and software side of the PLC to improve its reliability. On the hardware side, all IO interfaces are optically isolated, making it possible to physically isolate external circuits from the PLC's internal circuits. Shielding measures are used in each module to prevent radiated interference. Filtering technology is used in the circuit to prevent or suppress high-frequency interference. In terms of software, PLC has a good self-diagnosis function, once the system hardware and software abnormalities occur, the CPU will immediately take effective measures to prevent the failure from expanding. Usually PLC has a watchdog function.
For large PLC systems, you can also use dual-CPU redundant system or three-CPU voting system, so that the reliability of the system is further improved.
2. Simple and easy to learn the program, the system's design and debugging cycle is short
PLC is user-oriented equipment, PLC manufacturers take into account the skills and habits of field technicians, ladder diagrams can be used or simple instructions for industrial control form. Ladder diagrams and relay schematic diagrams are very similar, intuitive, easy to understand and easy to grasp, do not need to learn specialized computer knowledge and language. Designers can design, modify and simulate the debugging program in the design room, very convenient.
3. Simple installation, easy maintenance
PLC does not need a special machine room, can be directly run in a variety of industrial environments, the use of a variety of equipment on the scene and the PLC is connected to the corresponding IO terminal, can be put into operation. Various modules have operation and fault indication device, which is convenient for users to understand the operation situation and find faults.
4. Adopt modularized structure, small volume and light weight.
In order to adapt to the needs of industrial control, in addition to the overall PLC, the vast majority of PLC modular structure, PLC components, including the CPU, power supply and TO modules, etc. are modular design. In addition, PLC is much smaller in size and weight compared to general-purpose industrial control machine.
5. Rich IO interface module, strong expansion capability
PLC for different industrial signals (such as AC or DC, switching or analog, voltage or current, pulse or potential and strong or weak power, etc.) have the corresponding IO module and industrial devices or equipment (such as buttons, travel switches, proximity switches, sensors and transmitters, solenoid coils and control valves, etc.) directly connected. In addition, in order to improve the operational performance, it has a variety of human-machine dialog interface module; in order to form a local industrial network, there are a variety of communication networking interface module.