In brief
A fieldbus is an industrial communication system that digitally connects sensors, actuators and drives to the controller via a shared cable.
Contents
What is Fieldbus?
Before fieldbuses were introduced, every signal was wired individually from the field into the control cabinet. A fieldbus transmits many signals over a shared cable, reducing wiring effort and sources of error. Diagnostic and parameter data can also be transmitted. The protocols are described in the IEC 61158 series of standards. Instead of thick cable harnesses, a single bus cable is often sufficient, with distributed modules located close to the machine.
Classic fieldbuses work over serial two-wire cables, for example to RS-485, and connect controllers, distributed inputs and outputs, frequency inverters or valve terminals. Today, Ethernet-based fieldbuses are increasingly prevalent, offering higher data rates, real-time capability and easy connection to IT networks. For sensors at the lowest level, there are also point-to-point interfaces. Key ratings are protocol, transmission medium, topology, data rate, cycle time and connector system.
Faults are frequently caused by missing terminating resistors, damaged cables, poor shielding, incorrect addresses or defective bus interfaces. When replacing a bus node, the protocol, device description file and address must match. Replacement modules should therefore always be ordered in the correct bus variant.
In practice: maintenance and procurement
For every bus network, document the protocol, node addresses, device description files and firmware versions. In spare parts enquiries for bus modules, couplers or drives, always state the protocol used, as identical devices often exist in several bus variants.
Synonyms and abbreviations: field bus · industrial bus system · Industrial Ethernet · fieldbus system
Frequently asked questions
What is the difference between fieldbus and Industrial Ethernet?
Classic fieldbuses use their own serial transmission technologies with comparatively low data rates. Industrial Ethernet is based on Ethernet technology, supplemented by real-time mechanisms for automation. It offers higher data rates and can be connected more easily to IT networks. In the broader sense, Ethernet-based systems are now also referred to as fieldbuses.
What is a device description file?
A device description file describes the properties of a bus node, such as data volume, parameters and diagnostic messages, in a standardised format. The controller’s engineering software needs this file to integrate the device. When replacing with a different model or a new version, an updated file may be required.
How can a fieldbus fault be recognised?
Typical signs are failed nodes, sporadic communication dropouts or error messages in the controller. Diagnostic LEDs on modules and the controller’s diagnostic functions help to narrow down the fault. Common causes are cable and connector damage, missing terminating resistors, shielding problems or duplicate addresses.