Siemens offers a comprehensive range of PROFIBUS network components for electrical and optical transmission technology.

PROFIBUS is standardized in accordance with IEC 61158/EN 50170 for universal automation (PROFIBUS FMS and PROFIBUS DP), and in accordance with IEC 61158-2 for process automation (PROFIBUS PA).

Electrical network

• The electrical network uses a shielded twisted pair cable. The RS 485 interface works with voltage differences. It is therefore less sensitive to interference than a voltage or current interface. With PROFIBUS, the stations are connected to the bus via a bus terminal or a bus connector (max. 32 stations per segment).
• The individual segments are connected via repeaters.
• The transmission rate can be set in steps from 9.6 Kbit/s to 12 Mbit/s.
• The maximum segment length depends on the transmission rate.
• The electrical network can be configured as a bus or tree structure
• For applications in the intrinsically-safe area, the transmission technology compliant with IEC 61158-2 is used with PROFIBUS PA. The transmission rate in this case is 31.25 Kbit/s.

Characteristics

• High-grade bus cable
• Transmission method: RS 485 (acc. to EIA)
• Bus topology with bus terminals and bus connectors for connecting PROFIBUS stations
• Transmission method in accordance with IEC 61158/EN 50170 for universal automation (PROFIBUS FMS/DP), and in accordance with IEC61158-2 for the intrinsically-safe area (PROFIBUS PA)
• The DP transmission system of RS 485 (bit coding by means of differential voltage signals) is converted to IEC 61158-2 (bit coding by means of current signals) using the network components (DP/PA coupler or DP/PA link)
• Simple, universal installation and grounding concept
• Easy installation

Electrical PROFIBUS network configuration

Optical network

The fiber-optic cable variant of PROFIBUS has the following characteristics:

• Transmission link is insensitive to electromagnetic influences
• Suitable for long ranges
• Galvanic isolation
• Uses either plastic, PCF or glass fiber-optic cables
• Avoidance of overvoltage and equipotential bonding problems

Optical PROFIBUS with OLMs

Using optical link modules (OLMs) it is possible to construct an optical network in a linear, ring, or star topology. The maximum distance between two OLMs is 15 km. The transmission rate can be set in steps from 9.6 Kbit/s to 12 Mbit/s.

Optical PROFIBUS with integral interface and OBT

The optical PROFIBUS with integral interface and OBT is constructed in a linear topology. A cost-optimized solution is available for this in the form of devices with integral optical interface. Terminal equipment with an RS 485 interface can be connected via an Optical Bus Terminal (OBT). The maximum distance between two nodes is 50 m in the case of plastic fiber-optic cables. Special fiber-optic cables are available to cover distances of up to 400 m.

Hybrid network

Hybrid electrical and optical networks are possible. The transition between both media is implemented by the OLM.

In station-to-station communication on the bus, there is no difference between two-wire technology and fiber-optic technology. A maximum of 127 stations can be connected to one PROFIBUS network.

The optical transmission technology offers the following advantages:

• Fiber-optic cables made of plastic or glass are not susceptible to electromagnetic interference and therefore render the EMC measures required for electrical networks unnecessary
• No additional lightning protection concept is required in the outdoor area
• The potentials on the modules are automatically separated thanks to the characteristics of the conductor
• With fiber-optic cables, long distances to field devices can be bridged.

Network configuration combining electrical and optical PROFIBUS