What’s the first thing that comes to mind when you think of the word BUS? Probably the big, yellow cheese bus or your local public transportation system. But in the field of electrical engineering, this has nothing to do with the vehicle. BUS is an acronym for "Binary Unit System". A “Binary Unit System” is used to transfer data between participants in a network with the help of cables. Nowadays, BUS systems are standard in industrial communication, which can hardly be imagined without them.
How it all started
Industrial communication started with parallel wiring. All participants in a network were directly wired to the control and regulation level. With increasing automation, this meant an ever increasing wiring effort. Today, industrial communication is mostly based on fieldbus systems or Ethernet-based communication networks.
“Field devices,” such as sensors and actuators, are connected to a programmable logic controller (known as a PLC) by means of wired, serial fieldbuses. The fieldbus ensures fast data exchange. In contrast to parallel wiring, the fieldbus only communicates via one cable. This significantly reduces the wiring effort. A fieldbus works according to the master-slave principle. The master is responsible for controlling the processes and the slave processes the pending tasks.
Fieldbuses differ in their topology, transmission protocols, maximum transmission length and maximum amount of data per telegram. The network topology describes the specific arrangement of the devices and the cables. A distinction is made here between tree topology, star, cable 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 exchange in the form of data packets with all devices in a network. Real-time communication takes place in three communication levels. This is the control level and sensor/actuator level. For this purpose, uniform standards are created. These are managed by the Institute of Electrical and Electronics Engineering (IEEE).
How Fieldbus and Ethernet Compare
Ethernet enables real-time data transmission and transmission of larger amounts of data. With classic fieldbuses, this is either not possible or very difficult. There is also a larger address area with an almost unlimited number of participants.
Ethernet transmission media
Various transmission media are possible for the transmission of Ethernet protocols. These can be radio, fiber optic or copper lines, for example. The copper cable is most frequently found in industrial communication. A distinction is made between 5 line categories. A distinction is made here between the operating frequency, which indicates the frequency range of the cable, and the transmission rate, which describes the data volume per unit of time.
In summary, we can say that a BUS is a system for data transmission between several participants via a common transmission path. There are various BUS systems in industrial communication, which can also be linked to manufacturers.
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