Automation components in detail

The choice of one or more transmission media, i.e. the cables and conductors needed for networking, for an INTERBUS system varies. Whether we are dealing with copper cables, fiber optics or optical data links, a medium is available for all requirements.

Electrical isolation of different media

In many cases, data from an INTERBUS system is led through a copper cable using differential signal transmission in acc. with RS-485. One twisted-pair cable is needed for the supply line and one for the return line. A fifth wire serves as equipotential bonding between the modules because electrical isolation of the segments is stipulated in INTERBUS. With a data transmission rate of 500 Kbit a distance of 400 m between two devices is possible, due to the RS-485 point-to-point transmission. The integrated repeater function in every station results in an overall coverage of the INTERBUS system of up to 13 km. The INTERBUS design with fiber optic technology has the same structure as the copper technology because here too, data is transmitted with two fibers. It is then only necessary to convert current to light and vice-versa. Therefore, both copper and fiber optic conductors can be used in an INTERBUS system and it can also be retrofitted with fiber optic technology without problems.

FO/copper - Simple connection

Hybrid systems

Using different media in one system is not a problem because simple interface converters are available. A system becomes more secure when fiber optic technology is used. In an environment contaminated with electromagnetic fields, fiber optic technology without complicated shielding transmits all signals without interference. The stations are completely isolated from each other and equipotential bonding is not necessary. Using the right tools, the cables can be assembled easily and quickly. Three optic fibers are used in practice. They all support different transmission distances that always depend on several parameters, such as cable quality, transmission capacity and receiver sensitivity. The simplest version is the polymer fiber. It supports distances between two stations of up to 70 meters. The HCS fiber (Hard Cladded Silicia) consists of a glass fiber core with a plastic sheath. It can typically bridge a distance of up to 400 meters. Glass fiber cables are suitable for distances of up to 3600 meters. Due to the low cycle rate of INTERBUS, 'simple' transmission media can also be used without problems: With optical data links, for example, distances of up to 200 meters can be bridged via an infrared light beam.