Field Bus Communication

It is a data communication that aims to reduce or prevent failure in several loops. This results in the failure of a loop to affect the other control loops. The use of Fieldbus also functions as savings on cable routing because the addressing system carried out by Fieldbus allows many devices to communicate via one cable pair. Unlike HART technology, Fieldbus does not do linearization data that occurs on HART technology by using 4-20 mA analog signals to be converted, while Fieldbus technology uses data programming. You could say Fieldbus technology relies more on software engineers from all sides, such as checking, sending data in the control unit, calibrating, etc.


An automated complex of industrial systems such as manufacturing assembly lines usually requires an organized hierarchy of control systems. In this hierarchy, there is usually a Human Machine Interface (HMI) at the top, where the operator can monitor or operate the system. This is usually related to the middle layer of a programmable logic controller (PLC) through a non-time-critical communication system (eg Ethernet). At the bottom of the control chain is the Fieldbus that connects the PLC to the components that actually do the job, such as sensors, actuators, electric motors, console lights, switches, valves and contractors.


Organized Hierarchy The Fieldbus Control System works on network structures that normally allow daisy-chains, stars, rings, branches. Previously computers connected using RS-232 (serial connection) with only two devices can communicate.

This would be the equivalent of the currently used 4-20 mA communication scheme which requires each device to have its own communication point at the controller level, while Fieldbus is equivalent to the current LAN-type connection, which only requires one communication point at the controller level and allows several ( hundreds) of analog and digital points to be connected at the same time.

This reduces both the length of the cable needed and the number of cables needed. Furthermore, because devices that communicate through fieldbus require a microprocessor, some points are usually provided by the same device. Some Fieldbus devices now support control schemes such as PID controls on the side of the device, not forcing the controller to process. There are various kinds of Fieldbus standards. Some of the most widely used include:

1. AS-Interface
2. CAN
3. Interbus
4. LonWorks
5. Modbus
6. Profibus
8. CompoNet
9. SafetyBUS p
10. SERCOS interface
11. RAPIEnet

The last edition of the IEC IEC 61158 standard allows 8 technologies. This is a multiple layer hierarchy of automation protocols.


AS-Interface (Actuator Sensor Interface, AS-i) is an industrial network solution (physical layer, data access method and protocol) used in PLC, DCS and PC based automation systems. It is designed to connect simple I / O devices (binaries such as ON / OFF devices such as actuators, sensors, rotary encoders, analog inputs and outputs, push buttons, and valve position sensors) in discrete manufacturing and process applications using 2 single-conductor cable.

AS-Interface is an ‘open’ technology that is supported by many automation equipment vendors.

CAN bus (Controller Area Network):

CAN bus is a message-based protocol, designed specifically for automotive applications but now also used in other areas such as industrial automation and medical equipment. CAN bus development began initially in 1983 at Robert Bosch GmbH. [1] This protocol was officially released in 1986 at the congress’s Society of Automotive Engineers (SAE) in Detroit.

The CAN bus is one of five protocols used in OBD-II vehicle diagnostic standards.


is a serial communication protocol published by Modicon in 1979 for use with logic programmable controllers (PLC). Simple and powerful, it has since become one of the standard de facto communication protocols in industry, and is now among the most common ways available to connect industrial electronic devices. The main reasons for the wide use of Modbus in an industrial environment are:

  • It has been developed with industrial applications in mind
  • It is openly published and royalty free
  • It is easy to deploy and maintain
  • Raw bits or words move without placing many restrictions on the vendor

Modbus allows for communication between multiple departures (around 240) connected to the same network, for example a system that measures temperature and humidity and communicates the results to a computer. Modbus is often used to connect surveillance computers with remote terminal units (RTUs) in system control and data acquisition (SCADA). Many types of data are named for their use.


Profibus (Field Bus Process) is the standard for bus communication in automation technology and firstly promoted in 1989 by BMBF (German education and research department) and then used by Siemens. It should not be confused with the PROFINET standard for the Ethernet Industry. Profibus is not an open and royalty-free open protocol as older ones like Modbus.




Instrumentation Engineer

Related Articles

Back to top button