I. Interpretation
PLC is the abbreviation of Planar, Lightwave and Circuit in English, and Chinese translation is: planar optical waveguide (technology). The so-called planar optical waveguide means that the optical waveguide is located in a plane.
Second, the application scope of PLC
1, sequence control
Sequence control is the most widely used field of PLC, and it is also the most suitable field for PLC to play its specialty. PLC sequence control is used to replace the traditional relay sequence control.
2. Motion control
At present, PLC manufacturers have provided single-axis or multi-axis position control modules for stepping motors or servo motors. In most cases, PLC sends data describing the target position to the control module, and its output moves one or several axes to reach the target position. When each axis moves, the position control module maintains appropriate speed and acceleration to ensure smooth movement.
3. Process control
PLC can also monitor a large number of physical parameters, such as temperature, pressure, flow, liquid level and speed.
4. Data processing
In machining, the CNC system uses PLC as the main control and management system, which can complete a lot of data processing.
5. Communication network
Communication of PLC includes communication between host and remote I/O, communication between multiple PLCs, and communication between PLC and other intelligent control devices (such as computers, frequency converters, numerical control devices, etc.). ). Together with other intelligent control devices, PLC can form a distributed control system with centralized management and decentralized control.
Characteristics of PLC
1, high reliability and strong anti-interference ability.
In order to meet the requirements of industrial production for the safety and reliability of control equipment, PLC adopts microelectronics technology, and a large number of switching actions are completed by contactless semiconductor circuits. The influence of temperature, humidity, dust and vibration in industrial production environment is fully considered in structure.
Anti-interference measures such as isolation, filtering, shielding and grounding are adopted in hardware; In terms of software, measures such as fault diagnosis and data protection are adopted. These technologies make PLC have high anti-interference ability.
2, versatility and flexibility
PLC products have been produced in series, with various structural forms and great selection space. In addition, there are many kinds of PLC and peripheral modules, and users can flexibly combine different components into control devices with different hardware structures according to the requirements of different tasks.
3, the programming is simple and convenient
The programming of PLC application program is very convenient. Ladder diagram language very similar to relay contactor control circuit can be used for programming. This programming language is intuitive and easy to master, even for people without computer knowledge. Sequential function diagram is a structured block control flow chart, which can make programming easier and more convenient.
4. Perfect function and strong expansibility.
The input and output system of PLC has perfect functions and reliable performance, and can adapt to the input and output of various forms and properties of switch and analog.
5. The design, construction and debugging cycle is short and the maintenance is convenient.
The electrical components such as intermediate relay, time relay and counter in relay contactor control system appear in the form of "soft components" in PLC control system, and hard wiring is replaced by programs, so the workload of installation and wiring is less; Staff can also program in advance according to specific control requirements before the arrival of PLC, which greatly shortens the construction period.