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* taking quality readings with a PLC and sending the data to a database computer.
* distributing recipes or special orders to batch processing equipment.
* remote monitoring of equipment.

Larger Wide Area Networks (WANs) are used for communicating over long distances between LANs. These are not common in controls applications, but might be needed for a very large scale process. An example might be an oil pipeline control system that is spread over thousands of miles.

plc network -28.2

28.1.1 Topology

The structure of a network is called the topology. Figure 28.1 shows the basic net work topologies. The Bus and Ring topologies both share the same network wire. In the Star configuration each computer has a single wire that connects it to a central hub.

LAN

A Wire Loop Central Connection

Figure 28.1 Network Topologies

In the Ring and Bus topologies the network control is distributed between all of the computers on the network. The wiring only uses a single loop or run of wire. But, because there is only one wire, the network will slow down significantly as traffic increases.

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