With the application of microprocessor, the running speed of PLC is increased, making it more suitable for handling high-speed and complex control tasks. The difference between it and microcomputer is not very obvious.
The total price is low
The weight, volume, power consumption and hardware price of PLC have been decreasing. Although the proportion of software price has increased, various manufacturers have also lowered their prices accordingly for competition. In addition, the use of PLC can greatly shorten the design, programming and production cycle, so that the total price is further reduced.
The PLC system, the industrial bus computer and the DCS system penetrate each other, learn from each other, and develop in competition with each other. Promote the progress of industry.
Faced with the development of fieldbus, PLC products will be innovated again to meet the higher needs of industrial and civil control.
PLC communication and networking
The communication of PLC includes communication between PLCs, between PLCs and upper computers, and between PLCs and other intelligent devices. The PLC system and the general computer can be connected directly or through the communication processing unit and communication adapter to form a network to realize the exchange of information, and can form a distributed control system of “centralized management and decentralized control”, which can satisfy the factory automation (FA) system. According to the needs of development, each PLC system or remote I/O module is placed in the production site for distributed control according to their functions, and then the network connection is used to form a distributed network system for centralized management.
Taking Siemens’ SIMATIC NET as an example, in the system concept of Totally Integrated Automation (TIA) proposed by Siemens, the core content includes the integration of configuration and programming, the integration of data management and the integration of communication. The communication network is an important and critical component of this system, providing complete industrial communication between the components and the network.
SIMATIC NET consists of three main layers:
AS-I network – an international standard for communication between sensors and actuators, the scanning time is 5ms, the transmission medium is unshielded twisted pair, the line length is 300m, and the maximum number of slave stations is 31.
PROFIBUS——Industrial field bus, international standard for workshop level and field level, the maximum transmission rate is 12m/s, the transmission medium is shielded two-wire cable (up to 9.6km) or optical cable (up to 90km), up to 127 slave station.
Industrial Ethernet – an international standard for area and unit networking, with a network scale of up to 1024 stations 1.5km (electrical network) or 200km (optical network).
In this network system, the PROFIBUS field bus is particularly worth mentioning. PROFIBUS is one of the most successful field buses at present and has been widely used. It is an open field bus that does not depend on the manufacturer, and various automation devices can exchange information through the same interface. Numerous manufacturers provide high-quality PROFIBUS products, and users can freely choose the most suitable products. PROFIBUS has become the German national standard DIN19245 and the European standard pr EN50170, and has the largest number of users in the world.