The industrial automation systems is divide into several hierarchical level.Each of the stage or level has an appropriate communication level.which stage or level different requirements on the communication network.Industrial communication may be classified in different categories based on functionality-field-level networks,control level networks and information-level networks.at lowest level we use sensor and actuator buses to connect simple discrete devices,such as photo-eye,limit switch, or solenoid valve to controllers to computers
- The lowest level of the automation communication cycle is the field level, which includes the field such as ac/dc motors,valves,relays,sensors,bar code the task of the devices in the field level is to transfer between the manufactured product and the technical process.the data may be both type digital or analog for the field level communication widely used parallel, multi wire cables, and serial interface such as the 4 -20mA current loop has been widely used from the past.the serial communication such as RS232C, RS422 and RS485 are most commonly used protocols together with the parallel communication standard IEEE488.
Control level the information related to loading programs,parameter and data.in small controllers it may be necessary to load subroutines during one manufacturing cycle of program execution.the timing requirements it can be divided into two parts :cell sub levels and area sub levels
- Cell sub-level
For the cell level operations synchronization and event handling mainly required
short response time.this achieve by local area network used in communication network,many companies developed own proprietary networks for the cell level communication.after many things and efforts have been made for the standardization of the communication network for the cell level.The IEEE standard network based OSI architecture were developed
- Area sublevel
The area level consists a combination of cell groups.Cell are designed with application-oriented functionality.using area level controllers or process operators the controlling production targets machine startup and shutdown we are typically use control-level network for peer-to-peer network between controller such as plc, dcs and scada hmi. like profibus, controlnet for controller buses. Ethernet tcp/ip is use for upper-level control device and computers
- Cell sub-level
The information level is the top of a plant and industrial system.The plant level controller management information area levels and manage whole automation system.At the information level there exist large-scale networks
An industrial control network is defined as a system of interconnected equipment’s used to monitor and control industrial environments.its defind as a network used to connect various devices of different industrial application.There are different industrial network and identify right one for the right application is big issue.The network selected is allow us to communicate with all the interconnected device and right information should be available to the right user at the right time.to correctly analyze and select suitable industrial network for an application
If Computers communicate they have to know how information is to be exchanged and message format.transmitting and processing different kind of information are called protocols.protocols cover authentication,error detection and correction and signaling.
Popular Protocols are…..