Industrial communication networks Lesson 2 Industrial communication networks

Industrial Networks Classified into three levels based upon the type of data and devices that use the network. Enterprise: non time critical information Automation and Control: Real time I/O Field device: switches, output devices and drives

Industrial Networks

Enterprise Level Shares data between all segments Transfers non-time critical data Ethernet is preferred network because high speed, open-source protocol and competitive vendor pool In the past proprietary networks have been used, but this do not communicate with other networks. Ethernet has been implemented to bridge devices from different networks

Automation and Control Level Transfers data between the controller and the I/O devices it controls and to other controllers Data is high urgency – real time Determinism: data to be sent and received in a timely manner and verified is correct Reliability 24/7 schedule even in hostile environments Security Routers typically use to isolate networks and provide security

Field Device Level Networks Connects individual I/O devices to a PLC Replaces remote I/O racks, adapters, modules, and field wiring with a direct connection to intelligent switches and output devices Ease of installation Reduction of I/O wiring Error and diagnostic reporting Open networks and support different vendors Devicenet is the most common field level network for Allen Bradley controllers (others EtherCat, Serial RS-232, CANopen, etc

ETHERNET TCP/IP

Difference Ethernet/IP and TCP/IP TCP is an acronym with stands for Transmission Control Protocol. This protocol is responsible for managing the connection between a client and a server IP has two different meanings depending on how it is used: Industrial Protocol for Ethernet/IP and Internet Protocol for TCP/IP Ethernet/IP uses the Ethernet infrastructure to manage the connection between various automation devices such as robots, PLCs, sensors, etc. Based on the Common Industrial Protocol TCP/IP industrial protocol used is Modbus TCP/IP which is responsible for the transmission of the packets. TCP/IP is standard in most programming languages (C,C++, Matlab). Also Modbus TCP/IP is standard in most PCs.

Ethernet/IP Is an offspring of the Common Industrial Protocol CIP Developed for transferring data on DeviceNet and ControlNet (Fieldbus) networks. Advantage of speed and reliability of Ethernet. Never truly deterministic however good enough for industry Real time I/O at 100 Mbps, 20 times faster than ControlNet No additional hardware needed to communicate to any Ethernet network.

Adapters Connect devices such as controllers, PanelView terminals, drives to other devices Provide interface that converts data into a signal that can be transmitted on a cable and re-convert that signal back into data at destination device Make sure devices are Ethernet/IP compatible

Cable Cat 5 most common , also known as 10BaseT Limited to 100 meters between switches and or routers Can be shielded twisted pair (STP) or unshielded (UTP) STP thought more expensive than UTP is preferred in areas with high electrical noise, drives > 10 HP, or conductors carrying >100 amps, and if inside metal conduit Fiber optic run in extreme high electrical noise (immune to noise) Fiber optic more expensive and needs converters Fiber optic up to 1500 meters between switches

RJ45 Connector Wiring Category 5 Ethernet Cable uses 8 wires twisted to form four pair of wires. 2 standards for arranging the colors in the RJ45 connector, T568A, and T568B Cables can be wired straight through or crossover Straight through: are used to connect devices to switches and routers Crossover: used to directly connect two Ethernet devices together

Crossover cable Often use to directly connect a computer to an Ethernet/IP module for initial setup. The computer runs a software utility called BootP to set the IP address that the module will use on the network. A crossover cable reverses the TX and RX lines from one connector to the other to permit connecting a PC directly to an Ethernet Device. Usually color of cable is red to differentiate

Bus (Backbone) Topology

Ring Topology

Star Topology

Star Topology Connects each device through a separate cable or switch, creating segments or subnets Eliminates most message collisions (major factor in stablishing determinism) Allow for new nodes to be installed without disrupting existing nodes Failure of that node affect only that node Reduces network traffic by limiting multicast data from going to all nodes on the network by sending only to selected nodes

Routers Used to connect different devices together while maintaining isolation between the networks. Only messages with the correct address can cross the router from one network to another

Switches Intelligent Ethernet switches have replace hubs to reduce the number of message collisions in the network Collision occur frequently because more than one node tries to transmit at the same time Ethernet switch knows the address of each device on each port and stores address in memory. When a message is received, the switch decodes the destination address and sends the message only to the port of which the device is connected ControlLogix inputs mulitcasts to every node in the network. Intelligent switches can control multicast data, such as I/O to prevent overloading the network with messages