A fieldbus connects different sensors (sensing elements) and actuators (actuating element) in an installation for communication with a higher-level control unit (SPS). With this, as a rule, several participants send and receive almost simultaneously via one and the same line. To prevent data collisions, it must be specified who (identifier) says what (measuring value, command) when (initiative). There are standardized protocols for this.

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The first generation of the fieldbus technology was developed in the 1980s. The aim was replacement of expensive parallel wiring by a single line. This was made possible by changing from analog to digital signal transmission. Today, many different fieldbus systems with different transmission characteristics have been established on the market. Since 1999, fieldbuses have been standardized worldwide in the standard IEC 61158 (“Digital data communication for measurement and control - Fieldbus for use in industrial control systems”). The second generation of the fieldbus technology is based on real-time Ethernet.