Application of A-B fieldbus in dairy processing industry
Abstract: Dairy processing is a multi-region, multi-process coordinated control process. The project successfully applied the A-B equipment layer, control layer and information layer network to the automatic management of the entire production from process control to information processing, fully reflecting the intelligence, efficiency and flexibility of the A-B fieldbus system, which has played A huge role in improving the quality of customers’ products and economic benefits. The large-scale application of fieldbus technology in this project has a certain reference and reference for the design and development of production process control in other industries.
Key words: fieldbus dairy processing Rockwell automation
Project background: In 2002, a dairy factory in northeast China carried out production line expansion and renovation. The factory originally used a large number of PLC-5 and SLC500 series products, and connected together by DH+. This transformation, the plant’s production capacity will be expanded by more than half, and the transformation process involves the upgrading, replacement and deletion of the original control system.
Fresh milk is not easy to preserve, so the most critical thing in the entire project is how to completely switch the original functions and the control of the original on-site I/O equipment to the new system without stopping production. Secondly, how can we adopt a more reasonable, more advanced and more reliable scheme to adapt to the large number of applications of inverter, intelligent instrument and other equipment in engineering?
We choose the ControlLogix system, through its powerful network features, including EtherNet, ControlNet and DH+, successfully achieve non-stop switching and expansion transformation. After completion, the information layer of the system uses fast Ethernet as the link to realize the publishing and sharing of industrial control information. The control layer uses ControlNet as the backbone and is compatible with DH+, which effectively plans the system load and makes the network faster and more secure. The device layer uses RIO and DeviceNet, which not only greatly saves user investment and on-site workload, but also makes the information more comprehensive and realizes more flexible and intelligent control.
I. Overview:
Dairy processing is a complex multi-process coordinated control system, which includes product manufacturing system: milk source, pure milk, formula, concentration, drying, dry mixing, packaging; Service systems, such as steam, hot air, cooling, cleaning; In addition: water purification, sewage treatment and so on. Because the final product is closely related to human health, high requirements are put forward for the accuracy, reliability and real-time of the control system.
Compared with other brand automation products, A-B’s powerful network communication function is A significant advantage. Netlinx open network structure includes information layer, control layer and device layer three layers of network, NetLinx structure network service, CIP (control and information protocol) and open software interface together. Depending on the specific application requirements, users can mix and match one, two, or all three layers of the network, and can seamlessly transfer data between the networks. Under this network architecture, Rockwell Automation’s Logix platform provides users with compatibility of control in different formats.
Ethernet (Ethernet) technology has developed very rapidly in recent decades. Because of its extensive application and advanced technology, it not only monopolizes the communication field of commercial computers and the upper-level information management and communication in the field of process control, but also has been applied on a large scale in the field of industrial control, and is also the development trend of industrial field networks in the future. The EtherNet Industrial Protocol (EtherNet/IP) is an open industrial networking standard that uses IEEE 802.3 Physical Media and Data Link standards to provide real-time I/O messaging and peer-to-peer information communication. Typically, EtherNet/IP networks have an active star topology, with groups of devices connected to the switch in a point-to-point manner. Switches provide virtual connectivity that helps control network collisions and reduce network congestion. Among Rockwell Automation products, the PLC-5E series and SLC5/05 series and ControlLogix products provide Ethernet interfaces.
DH+ (Data Highway Plus) is an early industrial local area network that can be used for data transmission between PLCS, computers, human-machine interface products, etc. All the enhanced PLC-5 and SLC5/04 have a built-in DH+ communication port, plus DH+ uses cheap network media and a transmission distance of up to 3000 meters, it has been widely used in various industries. However, because the DH+ network uses the token transport protocol, the real-time transmission will be reduced when there are too many nodes (more than 20). In this case, it is not suitable for the control situations that require high real-time security and chain control.