Fiber optic cables and IP-based data communication via Ethernet are playing an increasingly important role in building automation. In this way, the information from the field level can ultimately be forwarded to the cloud and the processes can thus be controlled and monitored more effectively than before. An example of how systems differ across optical infrastructures from EKS angel can be connected reliably is the air conditioning and ventilation technology.

Above all, if the systems are to be networked across several buildings, optical fibers are, so to speak, the first choice. Because with them - unlike with copper cables - distances of several kilometers can be easily bridged. In addition, they offer protection against potential carryover. This means there are no equalizing currents that can damage the connected devices.

The air conditioning and ventilation technology is connected to DDCs (Direct Digital Control), which are installed in so-called information centers. There, the data is recorded and then forwarded to a central office, in which all information from the building management system converges. From this center the DDCs are controlled. Up-to-date information such as fault messages is also available on-site via touch panels. In addition, they can be sent to cell phones by caretakers or building engineers using a special GSM module.

Connection via Ethernet switches

The networks are mainly set up in a star shape. In this structure, each DDC has a separate connection to the control center, which is why bandwidth problems only play a minor role. The DDCs are in turn over Ethernet switches connected, in which the electrical signals of the air conditioning and ventilation systems are converted into optical ones and vice versa.

For high reliability requirements, a ring topology can also be used. There the data communication always runs in one direction and in case of an interruption additionally into the other one. Together with redundancy procedures that ensure fast switching times, the ring topology offers high network availability since, in contrast to the star structure, it also copes with the failure of a network node (single point of failure) or remains functional.

While system-dependent cabling and cable routing are required at the field level, there is a fixed basic installation at both the management and management levels. There are also differences in the processing of the data: The two upper levels are about large packets with a mainly acyclic transmission. On the field level, where the air conditioning and ventilation technology is installed, it is on the other hand, small data packets with predominantly cyclic transmission. In addition, there - unlike the other two levels - the transfer of data I real time and high availability of the network are important criteria.

Multimode fibers enable transmission distances of up to 5 km. However, with data rates ranging from 1 Gbit / s to around 550 m and 10 Gbit / s to 80 m, the distance is reduced, which is currently not relevant in the case of air conditioning and ventilation technology. Those who want to be on the safe side, however, can use single-mode fibers from the outset, which offer more than enough reserves with distances of more than 100 km and data rates of up to 40 Gbit / s.

Robust Ethernet media converters with low latency

Both fiber optic types consist of a glass core and a clad, which are firmly connected to each other, and differ only by the refractive index. The light propagates by total reflection of the rays in the core, which can be up to ten times smaller than a human hair with a diameter of 9 μm (singlemode) or 50 or 62,5 μm (multimode). Transmission losses have been reduced by modern manufacturing processes to the physically predetermined limits. This means that only the unavoidable microstructure of the high-purity glass disturbs the light wave and thus determines the physically possible lower limit of the attenuation.

Since FO consists of electrically non-conductive material, the data is always transmitted via an electrical insulator. In addition - unlike copper cables - no grounding or additional shielding is required. Also in terms of price, there is no significant difference between copper cables and fiber optic cables. However, 1 kg of this medium is as powerful as 1000 kg of copper. Finally, the raw material balance speaks a clear language. Because copper is actually too bad to move it in the form of cables. On the other hand, single- and multimode fibers are made of glass, which is available in almost unlimited quantities.

Practical alternative for retrofitting

Regardless of the type of fiber, care should be taken to ensure that enough fibers are available: even if only two or four fibers are currently needed, it is recommended to lay twelve or even 24 in order to be prepared for future requirements. For the connection of air conditioning and ventilation technology to existing optical infrastructures, in which there are only few or no free fibers, BiDi technology enables two-way communication over one fiber - normally two are required. However, the Ethernet switches must support this technique.

Although the connection technology has become ever simpler, single and multimode fibers are not easily assembled in the field. Therefore, the plugs should be connected by specialists and then the attenuation values ​​should be measured. This is the only way to ensure that everything works properly. Alternatively, prefabricated fiber optic cables can be used, which are available with attenuation protocol. However, this is recommended only for easily accessible cable routes and distances of a few 100 m, because the cables can otherwise be damaged during installation.

Ethernet switches | The data driver in the network

Ethernet switches provide a budget (difference between transmission power and reception sensitivity) with which the attenuation required for the respective fiber optic link can be bridged. However, this often increases gradually over time, for example due to loose connecting elements, dust and dirt, mechanical stress or changes in the network topology. Up to now, this could only be found out through complex measurements. Because network management and ScadaSystems can display the status of the switches, but not the status of the individual fiber optic links.

Highly available optical fiber links

The “Fiberview” monitoring system was specially developed for this task. The system is supported by the Ethernet switches of the "E-light" family. These switches are available for top hat rail mounting as well as in series installation devices for installation in meter cabinets in accordance with DIN 43880 and permanently monitor the budget of the respective fiber optic link for each port. The status is indicated by three LEDs on the front and a user interface, which can be accessed via the web interface, according to the traffic light principle. In the case of yellow, it is just above the defined system reserve of 3 dB. Since this early warning level is also signaled via a potential-free contact, it can also be evaluated centrally in Scada systems.

If Ethernet switches are not connected via pre-assembled fiber optics, it is advisable to use a splice box. Because the fibers can be neatly inserted and fixed in it. Patch cords can also be used for patch cords, which cost only a few euros to replace after a defect – unlike repairing a loose or detached fiber. With the splice boxes of the "Fimp" family, this connection technology is now available for use in switching and meter cabinets. Because splice comb, splice tray, couplings, pigtails, strain relief and Gland are already integrated, these boxes, with which up to twelve single or multimode fibers can be connected, can be installed quickly.