A European installation bus (EIB) is a system for automation in housing and functional buildings. The most recent version is the KNX standard, which specifies how sensors and actuators installed in a building can be connected to each other. It also specifies the communication protocol.
A European installation bus makes it possible to join and control lighting, shutters, shading devices, heating and cooling, and locking and alarm installations in a system. As a result of this technology, the remote monitoring of the building is also possible. Furthermore, the actuators can be controlled remotely by the user himself via a mobile telephone network. The control can also run in an automated fashion, via a computer.
A European installation bus is integrated nowadays, especially in the case of new housing and functional buildings. Such a system can be installed, even in the case of inexpensive prefabricated houses. Subsequent installation in old buildings is possible, but more difficult.
History of European Installation Bus
After various manufacturers developed systems for networking different devices in building engineering in the 1980s, they agreed upon a common standard in 1990. This standardization created the European installation bus. The first products appeared on the market in 1991.
Now there are nearly 4000 product groups from over 200 different manufacturers. The common protocol permits the cooperation of different equipment from different manufacturers, as well as replacement or expansion, if required.
Technology of European Installation Bus
A European installation bus is based on two networks that are separated from each other.
The conventional 230 V AC voltage network provides the power supply, while the 30 V DC voltage network parallel to it serves the controller. There is also a power net variant, where the control signals also are distributed via the 230 V supply network.
Now a controller is inserted between the consumer and the mains voltage. This device receives signals from the user or a computer via the 30 V line and switches the consumer with them. Sensors like switches, temperature or CO2 concentration meters can be analyzed by computer and as such, they can be changed into a control signal.
A European installation bus is based on a two-wire 30 V DC control line (red-black and white-yellow). However, only the red-black wire is used in this special UTP cable.
The usual conductor diameter is 0.8 mm. A maximum of 1 mm is stated.
The data exchange between different bus coupling units is done via telegrams. A special access method (CSMA/CA) takes care of telegram losses. With a transmission rate of 9.6 kbps, several 10,000 devices are theoretically possible.
Special IP-KNX couplers were developed for connection to PC technology.
Physical Structure of European Installation Bus
A European installation bus is divided into 15 ranges with 15 lines and 256 subscribers per main line or 64 subscribers per line. Up to 61455 different bus subscribers can be controlled separately with this. As such, the physical address 4.5.124 designates range 4, line 5, and subscriber 233.
64 bus subscribers can be integrated per line. This is limited by the voltage supply. Max. three line amplifiers can be used for expansion.
In order to expand the lines in the structure as well, they are connected via the main line by line couplers which are located in control cabinets. This main line can have max. 255 bus subscribers, as it needs a supply voltage itself. As described above, one main line connects a maximum of 15 lines and forms one range.
Backbones are used to connect ranges, and they themselves need their own supply voltage.
Logical structure of European Installation Bus
A European Installation Bus includes a freely programmable logical structure. Related actuators and sensors are connected to each other via a group address. Thanks to the easy programmability, the relation between the switch and the lamp (for example) can be changed at any time without laying cables.
As a European installation bus is an open standard and each manufacturer has full access to the required technological data, there is now considerable product diversity, however all of them can communicate with each other.
A European installation bus has a uniform packet structure:
Programming is performed with uniform software, the engineering tool software. The packet structure in the time sequence looks as follows:
- Control byte
- Source address
- Destination address
- DRL
- TPCI
- APCI
- Data/APCI
- Data
- Check sum
The control byte determines the priority of the packet. This can be used to differentiate between a standard packet and an expanded packet.
The source address is composed of two bytes. With this, first the range, then the line, and finally the subscriber is named.
The destination address can address a single receiver (uni-cast) or a group (multi-cast). The DRL byte defines which of the two options applies.
The DRL byte is one byte long and defines whether the destination is a physical address or a group address.
The communication on a transport layer is described by the transport layer protocol control information (TPCI). The application layer protocol control information (APCI) on the other hand is in charge of reading, writing, and answering communication.
The data are described by the “EIB interworking standard”. With this, there are 15 different formats:
- EIS 1 Switching
- EIS 2 Dimming
- EIS 3 Time
- EIS 4 Date
- EIS 5 Value, floating point number 16 bit, proprietary format
- EIS 6 Relative value, 0 … 100 %
- EIS 7 Drive control
- EIS 8 Forced control
- EIS 9 Floating point number, 32 bit, IEEE 754 single
- EIS 10 16-bit value
- EIS 11 32-bit value
- EIS 12 Access control
- EIS 13 ASCII characters
- EIS 14 8-bit value
- EIS 15 Character string
The check sum is formed by settling of all bytes sent so far.
A European installation bus is available for Windows-based as well as for Linux-based control.