Fieldbus Systems
Fieldbus systems are the means of connecting individual progammable logic controllers (PLC's) to each other, and to devices such as encoders and local input/output stations. They were /are designed to decentralise the very large individual controllers that have very many inputs and outputs. Some manufacturers of PLC's use their own "in-house" systems, which can only link their own branded products one to the other.
Most popular since the 1990's, have been the "open" systems where any manufacturers can (if they choose) supply a product that can communicate with any other using the same system. These systems, or protocols, each use different cable methods (architecture) and different ways of communicating. They are not interchangable.
Examples of the most popular today are PROFIBUS (& PROFI-SAFE), DEVICENET, INTERBUS, MODBUS, CAN(& CANopen). In turn most of these can communicate "UP" to PCs via ethernet connections, and "DOWN" to simple input/output devices using ASI by using gateways.
The chances are that you are on this page looking for a particular product, probably an encoder, maybe a PLC, that will intergrate into an existing network. So we have made no attempt to differenticate between protocols, or explain the pros and cons of any. The Hengstler range of absolute encoders "ACURO" includes versions which communicate as a slave or node for PROFIBUS, CANBUS, CANopen and DEVICENET. For information in some detail visit our dedicated encoder website
Fieldbus Trends In Europe
Profibus DP appears to have become market leader, whilst in the USA DeviceNet is strong. The trend appears to be towards individual PC to PC communication using ethernet, connected by the same protocols to the slave stations of encoders, local feeders and input/output stations. These ethernet protocols include ProfiNet & EtherCat. These networks are now able to directly interface with individual I/O slaves although the range is limited.
AS-Interface (AS-i)
AS-i is a standalone bus system in it's own right, but is most frequently used instead of hard wiring, to connect sensors and actuators to PLCs, which in turn use communication gateways to the higher level bus systems introduced here.
