What is a BUS?
Jen Chen | August 31, 2022
When people think of the term “bus”, most of them immediately think of a school bus or public transport bus. But in our case this has nothing to do with the vehicle. BUS is an abbreviation that stands for “Binary Unit System”.
A “Binary Unit System” serves to transfer data between participants in a network. This is analogical to the human nervous system. Here data or information is sent from our sensory organs, e.g. the eye, via a nervous system to the brain. There they are processed into further information or commands and then, for example, passed on to the hand. Nowadays, BUS systems are standard in industrial communication and can hardly be imagined without them.
How everything began:
Industrial communication started with parallel wiring. Here all participants were directly wired in a network with the control and regulation level. With increasing automation, this meant ever greater wiring effort. Today, industrial communication is mostly based on fieldbus systems or Ethernet-based communication networks.
The so-called “field devices”, such as sensors and actuators, are connected to a programmable logic controller (known as PLC) via cable-connected, serial fieldbuses. Here the fieldbus ensures a fast exchange of data. In contrast to parallel wiring, the fieldbus only communicates via one cable. Thus the cabling effort could be reduced significantly. A fieldbus operates using a host and device system. Here the host is responsible for controlling the processes and the device processes the pending tasks.
Differentiation from fieldbuses
The fieldbuses differ in their topology, their transmission protocols, the maximum transmission length and the maximum amount of data per telegram. The network topology describes the specific arrangement of devices and cables. A distinction is made here between tree topology, star, line or ring topology. Known fieldbuses are Profibus or CANopen. The bus protocol is the set of rules under which communication takes place.
An example of BUS protocols are the Ethernet protocols. Ethernet enables data to be exchanged in the form of data packets with all devices in a network. Here, real-time communication takes place at three communication levels. This is the management level, the control level and the sensor/actuator level. Uniform standards are formed for this purpose. These are managed by the Institute of Electrical and Electronics Engineering (IEEE).
Comparison fieldbus vs. Ethernet
Ethernet enables real-time data transmission and the transfer of larger data volumes. With classic fieldbuses, this is either not possible at all or only with great difficulty. There is also a larger address range with an almost unlimited number of participants available.
Ethernet transmission media
Various transmission media are possible for the transmission of Ethernet protocols. These can be e.g. radio, fibre optic cables or copper cables. Copper cable is most commonly used in industrial communications. A distinction is made between 5 cable categories. A distinction is made between operating frequency, which indicates the frequency range of the cable, and transmission rate, which describes the data volume per time unit.
In summary, we can say that a BUS is a system for data transmission between several participants via a common transmission path. In industrial communication there are various BUS systems, which can also be manufacturer-specific.
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