What is Fieldbus?

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.

But what is fieldbus? Basically, Fieldbus works on a network that permits various topologies such as the ring, branch, star, and daisy chain.

Prior to Fieldbus protocols, 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.

A primary benefit of Fieldbus is for field connected devices. For instance, consider you have several field devices that are quite a distance from your controller.

With Fieldbus devices such as sensors, motors, lamps, switches, these devices are connected to an “I/O data block”, which is then connected to a “field distribution device”, which is connected to a Fieldbus power supply, then finally connected back to the Programmable Logic controller.

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.

This is not to say that every protocol is dedicated to a particular manufacturer and must connect to the proprietary controller. For instance, Profibus is a widely used protocol that can connect to Allen Bradley, Siemens, Modicon, etc.

The same applies to the universal protocol of Modbus.

However, some protocols do not play well with others. ControlNet is an example that cannot integrate into a Siemens processor.

With this information, as you can see, there should be great care taken when designing your plant control system, including the communications network, and specifically the device layer if considering Fieldbus devices.

Do your research and make sure that all family members like each other and are willing to communicate together.

Thanks again for reading. Leave your questions and comments and we’ll chat with you soon!

Happy learning,

The RealPars Team

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