Fieldbus Technology & Output Types

Fieldbus is a name given to a collective group of standardised network protocols used within machine automation and system controls.

These protocols are used to connect Programmable Logic Controllers (PLCs) to the components which do the work of automation, for example, sensors, actuators, lights, switches, valves, contactors and encoders.

The object of a fieldbus system is to enable the PLC to instruct the output device to change its status (i.e. move, return, on/off) and to receive information from the same device or other devices on the same network.

In the early days of PLCs, this was done with many cables (multi-core wiring, cable looms and harnesses) each directly hard wired to a component.

A fieldbus system replaces the mass of cables with typically just two wires so that we can call a fieldbus system a digital, two way, serial or two-wire system.

Fieldbus systems share a significant advantage over old hardwired systems. Cable elimination, speedier commissioning, and fewer fault opportunities all combine to reduce both capital expenditure and operational expenses in automation systems.

Manufacturers of automation PLCs started to develop in-house bus systems which were limited to their products in the 1980s. The need was for any manufacturer of input/output devices (sensors, actuators) to be able to connect using the same fieldbus protocols.

From this came the open fieldbus systems that we know today. An open fieldbus is one which is open to any manufacturer to build into their product using the desired fieldbus protocol.

Fieldbus protocols and other output types are described in the table below. There are many protocols to choose from; however, we have listed the most popular and those which are readily available within our encoder range.