Fieldbus refers to the mean of communication with input tools such as switches and sensors and with output tools such as indication lamps, drives, valves, and much more without connecting every individual device back to the controller that is industrial PC, PLC, and others. Hence, you can say that Fieldbus communications help to minimize costs.
Fieldbus refers to a group of protocols that are applied in the industrial sector and is about how Fieldbus control platforms work and function. Before Fieldbus protocols, industrial computers were connected through serial communications.
As known, serial communications allow only two devices to communicate per connection. On the other hand, Fieldbus protocols enable multiple digital points and analog to connect all together. This minimizes both the length of the cable required and the number of cables needed.
The Fieldbus protocols have been standardized by International Electrotechnical Commission (IEC) as IEC61158.
Understanding the Concept of Fieldbus Communications
Fieldbus communication works as a digital two-way multidrop transmission linkage between smart field devices. It is a local area network focused on commercial automation. It has enabled distributed control networks to replace centralized control networks and aligns the isolated field tools like actuators, smart sensors, controllers, and transducers.
In process control, the two Fieldbus technologies used are Foundation Fieldbus H1 and PROFIBUS-PA. Fieldbus communication enables reading data from field devices like smart sensors and writing data into it. Moreover, two-way communications lead to cost reduction and massive cable savings. A Fieldbus interface unit should be incorporated into the Fieldbus device to facilitate proper communication.
Foundational Fieldbus Topologies
Fieldbus communications functions upon a network that enables several topologies like the branch, ring, daisy chain, and star. This proves that Fieldbus is not for a single type but rather represents a group of protocols. The subsequent section will help you to understand different Fieldbus topologies in detail.
Fieldbus Daisy-chain Topology
It is the simplest method to connect Foundational Fieldbus and H1 devices, wherein every device connects to two cables leading to an unbroken chain network from the end to the other end of the segment. Although it has a major disadvantage, it cannot remove any device in the loop without disturbing the network’s continuity.
Disconnecting any instrument in the segment significantly causes “downstream” devices to lose signal. This is an intolerable liability in the most industrial arena, as it complexes servicing and maintenance of individual devices on the segment.
Fieldbus Bus Topology
In a bus topology, short “spur” cables link devices in a segment to a longer “trunk” cable. Quick-disconnect couplings or terminal blocks—within every junction box offers an appropriate way of disconnecting individual tools from the segment without disturbing data communication with the other tools.
The standard alignment for a “bus” topology is to reduce the length of every bus cable such that it can reduce the delay of the reflected network off the unterminated drop ends. The addition of terminators at the end of the bus cable is prohibited as in any electrical continuous network segment only two termination resistors are permitted.
Fieldbus Tree or Chicken Foot Topology
In tree topology, a long trunk cable ends at a multi-point junction in link to various field tools and their spur cables. Most Foundational Fieldbus network looks like an amalgamation of “tree” and “bus” topologies, wherein several junction tools functions as connection points for two or more field devices per junction.
Fieldbus Variants
There are several different Fieldbus variants accessible such as Profinet, AS-I Interface, Ethernet/IP, CC-Link, Sercos the automation bus, Modbus, DeviceNet, Ethernet, Varan, Ethercat, Canopen, Sercos Interface, Ethernet Powerlink, CompoNet, SmartWire-DT, IO-Link, and Profibus.
There are several Fieldbus variant solutions accessible as the makers of automation devices produced proprietary Fieldbuses with varying functions and features to best manage the market niche and to match with one another on a technical aspect. Hence, it can be said that few bus cables are effective at specific functions as compared to others.
Most Fieldbuses considered themselves to be “open” because of market pressure. This is so as large-scale industries wish to connect and utilize the installed control unit (for instance, PLC) to communicate through the Fieldbus to maestro tools from various makers to significantly “talk” to the control platform.
Industrial Communication Levels
Industrial communication constitutes to be a huge part of industrial automation. It is divided into three categories or levels as mentioned.
- Plant level: It is regarded as the final level of industrial communication as it is accountable for receiving and transferring business-level data of communication to the lower levels of plants.
- Cell level: This stage shifts data from the device to the plant level. Some standard communication protocols relate to the controllers at the cell level communication.
- Device level: This level enables the communication between field sensors to controllers. It is accountable for transferring process data and reputes the procedure to cell-level devices.
Conclusion
Fieldbus is an open architecture that is developed and administered by the Foundation Fieldbus. One of the most significant features of Foundation Fieldbus is its ability to gather and transfer huge amounts of data- not only control signals and process variables but also different types of devices and process data. Other main benefits of Fieldbus are it reduces wiring costs, improves online monitoring and diagnostics, reduces installation and start-up time, improves local intelligence in the devices, and facilitates interoperability between manufacturers.
