Application of the hottest Ethernet in automation

2022-08-08
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The application of Ethernet in automation

the development of computer and network technology has triggered profound technological changes in the field of control. The development of control system structure towards networking and openness will be the main trend of control system technology development. As the most widely used local technology, Ethernet has been more and more used in the field of industrial automation and process control

1. Ethernet technology introduction

generally speaking, the control system network can be divided into three layers: information layer, control layer and equipment layer (sensing/execution layer). Traditional control systems mostly use Ethernet in the information layer, while different fieldbuses or other special networks are generally used in the control layer and the device layer. At present, Ethernet has penetrated into the control layer and device layer. Many PLC and remote i/o suppliers can provide products that support tcp/ip Ethernet interfaces. There are three main reasons why ether has brought a storm like revolution to the automation market: the stimulation of low cost and the improvement of speed; Modern enterprises have more and more requirements for real-time production information; Openness and compatibility of ether

in the early Ethernet, multiple nodes shared the same transmission media, which was called shared Ethernet. The communication between nodes was broadcast, which was prone to conflict. Shared Ethernet uses csma/cd technology to avoid conflicts, that is, the sender will pause sending when detecting conflicts, and then resend it after a random delay for a period of time until it succeeds. Because the delay time is random and cannot be known in advance, the time response of shared Ethernet is uncertain and cannot be used in strong real-time occasions

the emergence of Switched Ethernet overcomes this shortcoming. The switch of Ethernet is a multi port bridge in the data link layer (the second layer of iso/osi reference model), which can also be said to be an intelligent distributor. The switch divides the network it manages into many physically isolated and logically interconnected nodes in a star topology. Each node establishes a separate physical connection with the switch. When communicating, the exchange opportunity establishes an exclusive full duplex channel between the sending port and the receiving port. It has all the bandwidth of Ethernet and avoids conflicts

while obtaining certainty, the transmission speed of Switched Ethernet is also greatly improved. Gigabit Ethernet has been popularized, and 10gb/s switching is being developed to prevent melt stagnation or adhesion. When Ethernet is used in information technology, the application layer includes HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), SMTP (simple email Transfer Protocol) and telnet (remote login). These tcp/ip based protocol clusters have become the de facto network standards in the industry and play a key role in the interconnection of different network systems from different manufacturers. However, when Ethernet is used in industrial control, real-time communication, objects for system configuration and application protocols of engineering models are embodied in the application layer

the development of industrial Ethernet and Internet technology will completely change the network architecture of traditional industrial enterprises. Industrial Ethernet has been extended from the information layer down to the control layer and equipment layer. After adopting the Ethernet architecture, the location of the controller can also break through the limitations of the traditional network architecture, which can be located on the site or in the central control room. At present, controllers and even remote i/o support Ethernet more and more. Web servers have been integrated in some controllers and remote i/o modules, which allows users of the information layer to directly obtain the current state values in controllers and remote i/o modules like users of the control layer. Manufacturing enterprises that adopt Ethernet architecture and open software systems are also known as "transparent factories"

in addition, real-time remote monitoring of industrial production process can be realized through the Internet, and real-time production data can be combined with ERP system and real-time user needs, so that production is not only order oriented production, but directly oriented to opportunity and market "electronic manufacturing", so that enterprises can adapt to the requirements of economic globalization

2. Serial port technology

Ethernet, as the main communication backbone of the IT industry, is a well-known fact, and has been widely used in the information industry, which is closely related to human life. In the face of this trend of networking, industrial automation systems, as the infrastructure of all industries, also widely use tcp/ip Ethernet as the system communication interface, and actively develop networking technologies and products that are more in line with industrial standards to improve the ability of system automation, so as to achieve the goal of reducing costs and improving competitiveness

however, in the process of system networking, because many traditional serial port devices do not have the ability to connect, there must be a scheme of serial communication to tcp/ip network in the transmission of control instructions and device information. The serial communication network technology is simple, easy to use and cost-effective. It is an ideal choice for system networking. Now, the nport series serial port server of moxa has appeared in the market

using the standard serial port driver of moxa, the serial port of moxa can be simulated as a remote COM port without changing the original application software or communication components of the system that use serial communication. The advantage is that with the driver support of windows and linux/unix, the nport family can immediately enable serial port devices to connect. The nport family of devices connected to the server contains a complete tcp/ip protocol. It can package serial port data into TCP packets, convert them into frames that can be transmitted on Ethernet, and transmit them to the Ethernet card of the host. After the host unpacks the packet with its own tcp/ip protocol, the application can receive complete serial port data

through the TCP port of nport family, the serial port data can be accessed by tcp/ip socket instead of driver. This solution is suitable for all systems with tcp/ip connection function. Making the serial port device have tcp/ip network interface can improve the efficiency of enterprise management and original work. Tcp/this is an acceptable feature for OCS. IP network can be managed remotely and flexibly, which greatly reduces the system fault maintenance and labor cost. It is a low cost-effective serial port device management mode

3. DCS system design based on Ethernet

3.1 taking the DCS system of a gypsum powder production line as an example, the principle: the gypsum powder production line is divided into several parts, such as crushing, grinding, frying and packaging

crushing: the raw material is sent to the primary crusher for crushing, and the raw material after primary crushing is sent to bunker 1 by the elevator. There is an electric vibrator under bunker 1. Start the electric vibrator to send the raw material after primary crushing to the secondary crusher for secondary crushing, and the raw material after secondary crushing is sent to bunker 2 by the elevator. After the electric vibrator under bunker 2 is started, the crushed raw material can be sent to the mill for grinding

grinding: the crushed raw material enters the mill for grinding. The milled powder is sent to the preheating bin by the cutter 1 # through the elevator and cutter 2 # and the powder in the preheating bin is sent to the frying pan through the double cutters 3 # and 4 # below for frying. Among them, the material level of the powder in the preheating bin is measured by the material level sensor and output to the input channel of the PLC simulation block after being transmitted

frying and packaging: the powder is sent into the frying pan through the double reamers 3 #, 4 # for frying. When the material level of the powder in the frying pan reaches the upper limit, stop the double reamers 3 #, 4 #. While heating the wok, stir the powder with a mixer. When the powder temperature reaches the temperature setting value, start the valve motor, and the powder will be discharged into silo 3. When the material level of the powder in the frying pan reaches the lower limit, start the double reamers 3 #, 4 #, and the powder in the preheating bin enters the frying pan, so that the temperature of the frying pan is lower than the temperature setting value, stop the valve motor, and the powder enters the next round of frying. The clinker in silo 3 is sent to silo 4 by cutter 5 # through the elevator, and then output and packaged by cutter 6 #. Among them, the temperature of the powder in the frying pan is measured by the temperature sensor and output to the input channel of the PLC Analog block after being transmitted; The output speed of cutter 6# is controlled by frequency converter to adjust its output speed. The process flow diagram is omitted due to space limitation

3.2 system hardware structure design

the system uses Ethernet technology and adopts centralized management and decentralized control. According to the control requirements of crushing, grinding, frying and packaging of gypsum powder production line, three cpm1a Omron PLCs are used to realize control

this system selects 1-to-3 serial port servers. Just install windows 95/98/me, Windows NT, and windows 2000 native com drivers on the upper computer, set the IP address for the moxa multi serial server, the upper computer communicates with the moxa nport server through the laboratory local area, and the lower computer (PLC) communicates with the moxa multi serial server through the RS-232 converter, and assigns the virtual COM port. The upper computer configuration software needs to design all the system configuration programs of the lower computer, Establish the corresponding com3-com5 hardware equipment to set up the human-machine interface configuration of the system. The remote monitoring of the system can be achieved by accessing the upper computer (the same as the Ethernet scheme, it is necessary to publish the web page on the configuration software). The remote computer can directly access the IP address of the moxa multi serial server, directly read tcp/ip packets, and conduct remote monitoring of the network. The specific design is that the PLC of crushing station is COM3, the PLC of grinding station is COM4, and the PLC of frying and packaging station is com5

this system can realize remote control through Ethernet. Compared with the traditional fieldbus mode, it has the characteristics of low cost, long control distance (computers connected to the network can monitor the system), easy combination of management and control, etc

3.3 system monitoring software design

the system monitoring software adopts Kingview configuration software. Because the network structure of Kingview is a flexible client server model, the client server is relative. According to the system network structure, the system has hardware aspects. According to Article 6.3 of the national standard gb/t2611 (2) 007 "general technical requirements for laboratory machines", it has clearly proposed that electrical equipment should have the ability to protect personal safety and avoid electric shock, and has made detailed provisions. The management station is divided into crushing station, grinding station and frying and packaging station. Each workstation is installed with Kingview 6.0 network version respectively. Etheric architecture. You need to select connection in the "network settings" item of the configuration king of each workstation. The management station is set to generate the interface that needs to be remotely monitored and browsed through the Internet for the login server and web server server, and you need to set the folder under the path of the project on this site as the sharing method. Then "customer configuration" is carried out in the "network settings" item to define the customer function of the local computer in the network, and it can act as a customer of multiple sites. Only one login server in a system selects the management station. The premise of the above configuration is that all stations in the network need to be in the network and can communicate regularly

network information transmission is the reference of network variables. Kingview can directly reference variables in the network

4. It is concluded that the development trend of industrial automation should be distributed, open and informatization. The distributed structure is a network that can ensure that each intelligent module in the network can work independently, reaching the concept of system risk dispersion; Openness means that the system structure has an accurate interface with the outside world, otherwise the pressure on the jaw will cause the experimental data Department to connect the system with the outside network; Informatization is to make the system information capable of comprehensive processing, and combine it with network technology to realize network automation and management and control integration

automation based on Ethernet technology has low cost and openness. It can realize remote control, easy to combine with management, and realize the integration of management and control, which is also one of the development directions of automation. The above system has been successfully applied in the current

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