Fieldbus isn’t really one thing but more of a collection of things. Fieldbus is a group of protocols that are used in the industrial arena.

The Fieldbus protocols have been standardized as IEC61158.

Prior to Fieldbus, industrial controller systems were connected using RS232 serial communications.

As you know, serial communications allowed only two devices to communicate.

Whereas today, the Fieldbus connections are more closely compared to the typical Ethernet connections where you can connect multiple field devices to a single connection point that would then connect to the controller.

However, Fieldbus is not a connection type, per se, but instead, a description used to indicate a group of protocols.

There are several protocols in the group such as ControlNet in the Allen Bradley family, Modbus, Profibus, EtherCAT, HART, CIP, and many more.

The connections to the Fieldbus components, with the exception of the field devices themselves, are single cable connections. This connection scheme may vary depending on the Fieldbus protocol that you are using.

This type of field device connection saves on wiring runs that would have to go all the way back to the controller.

As you can see, this type of device wiring would have many benefits when the distance is an issue.

As you can imagine, your controller system will need to have a communications module that will be able to establish communications with the field devices.

In the case of ControlNet, you would need a ControlNet module, Profibus would need a Profibus module, etc.