Bus systems and transmission systems

Building control or home automation systems measure, control and manage the entire complex of building services by programmable microprocessors. Mostly, bus systems are used for these purposes. The technical term 'bus' originated from computer engineering, where various peripheral devices were connected to one computer - in other words, for networking. Today, communication bus systems are also used in automotive engineering, industrial automation and in building automation. Data can be communicated by serial or by parallel transmission:

• The parallel bus consists of several lines running in parallel. Each line has been assigned a specified function. Parallel buses are contained in data-processing devices (personal computers), for instance, because here the transmission paths are short, and a high speed of transmission is required.

• Serial bus systems are used for data transmission across long distances. Transmission reliability is better than with parallel bus systems, and less material is demanded since only two data lines are necessary for transmission. For data transmission inside buildings, serial bus systems are used.

In the building sector, different bus systems are common, some of which will be described in this chapter (Harke, 2004).

15.2.1 European Installation Bus (EIB)

Devices that are connected to a bus system must be able to communicate with each other. This is why a uniform standard is required; otherwise, products made by different manufacturers could not be installed without causing problems. To solve this problem, the European Installation Bus Association (EIBA) was founded in Brussels in 1990; among its foundation members were 80 companies from the installation industry. They shared the aim of promoting an open, decentralized bus system that was tailored to the needs of electrical installation and was suitable for applications in functional and residential buildings. From this, the European Installation Bus (EIB) system emerged, which was commercially available as early as 1993.

Source: J. Reiss, Fraunhofer Institut für Bauphysik, Stuttgart

Figure 15.2.1 Interconnection of various building disciplines with the European Installation Bus (EIB) system

Source: J. Reiss, Fraunhofer Institut für Bauphysik, Stuttgart

Figure 15.2.1 Interconnection of various building disciplines with the European Installation Bus (EIB) system

EIB distinguishes between sensors as command-giving components (for example, control buttons, temperature sensors, etc), actuators as command-accomplishing components (motors, regulating valves, etc) and controllers as freely programmable components for logical functions (see Figure 15.2.1). Sensors, actuators and controllers are referred to as bus devices. All devices (sensors/ actuators) that are connected to the EIB bus line share the same principle of construction: every participating device comprises a bus coupling unit (BCU), including the application interface (AST), an application module (AM) and the application software (AS). Figure 15.2.2 illustrates the general configuration of an EIB participating device.

BUS line

User interface

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Source: J. Reiss, Fraunhofer Institut für Bauphysik, Stuttgart

Figure 15.2.2 General configuration of an EIB device

The bus coupling unit receives the telegrams as information on the bus line and then transfers the command to the application module (for instance, an actuator). Every device (sensor/actuator) participating in the EIB system is given its own name, which is referred to as the physical address. This address is unique within the whole EIB system and is defined by the place of installation as an area/line/device.

The EIB system features a hierarchic arrangement of the participating devices. This topology facilitates an easy survey of small and large systems. The participating devices and their interconnections can be recognized at first glance. The smallest unit is the EIB line segment (see Figure 15.2.3). An EIB line segment requires an EIB voltage supply and comprises up to 64 participating devices. An EIB line consists of up to 4 line segments with 64 devices each (see Figure 15.2.4).

Source: J. Reiss, Fraunhofer Institut für Bauphysik, Stuttgart

Figure 15.2.3 EIB

devices connected to a line segment

Source: J. Reiss, Fraunhofer Institut für Bauphysik, Stuttgart

Figure 15.2.3 EIB

devices connected to a line segment

Source: J. Reiss, Fraunhofer Institut für Bauphysik, Stuttgart

Figure 15.2.4 Configuration of an EIB line

The individual line segments are connected via so-called repeaters or line amplifiers. The repeaters separate the line segments galvanically, but they do transmit the EIB telegrams. Hence, a complete EIB line consists of maximally 256 EIB devices. If more than 256 devices are required, the line can be connected to the so-called main line by means of a line coupler (LC). The main line will then connect the various EIB lines to one another (see Figure 12.2.5). In addition, 15 lines can be combined into an area by means of an area coupler (AC). The area line connects a maximum of 15 area couplers to each other (see Figure 15.2.6).

All participants exchange information according to exactly specified rules - namely, by means of the bus protocol. The EIB topology thus includes the line, the principal or main line, and the area line. The smallest EIB layout consists of a voltage supply, a sensor and an actuator.

Source: J. Reiss, Fraunhofer Institut für Bauphysik, Stuttgart

Figure 15.2.5

Configuration of a main line

Every line segment contains an individual EIB voltage supply system (SV), which ensures that the remaining lines will maintain operation if one line segment suffers a blackout. The line coupler also features a so-called filter function. This function serves to transmit telegrams that are shared by several lines. Simultaneously, any messages that were sent from other lines or areas and that do not refer to participants within the same line are blocked. The same holds for the area coupler. Due to this hierarchic structure and the application of the filter function by line and area couplers, the data traffic is reduced. This also considerably simplifies putting the system into operation, as well as shortens diagnosis and maintenance.

In the standard design, EIB wiring is done using a so-called 'twisted pair' as a two-wire bus. Nevertheless, four-wire bus cables are also laid (with two wires kept in reserve). The cables YCYM 2 x 2 x 0.8 and J-Y(St)Y 2 x 2 x 0.8 can be used for these purposes. The overall length of all cables laid in one line segment must not exceed 1000 m. The maximum cable length between two bus appliances must be shorter than 700 m.

The standardized EIB voltage supply works in a potential-free form and provides a 29 V direct current. The information is transmitted over the bus cable as the voltage difference between the two bus wires. Data encoding is strictly binary. Data is transferred at a transmission rate of 9600 bit/s. An EIB telegram consists of a control field (8 bits), the source address (16 bits), the target address (17 bits), another control field (7 bits), the useful data proper (8 to 128 bits) and the data protection field (8 bits). The source address indicates the physical address - that is, in which range and in which line the emitting appliance is located. The target address states the communication partner that is to receive the information.

In the EIB bus system, the lines can be laid in linear, star-type or tree shapes. Bus appliances can be installed in series inside the circuit distributors as concealed or surface-mounted appliances.

For programming purposes, the EIB tool software (ETS) provides a standardized tool for all EIB products. ETS allows processes such as assigning physical addresses and group addresses, downloading applications to the EIB appliances, entering designations and assigning parameters to the appliances. In addition, the EIB tool software offers various diagnosis features (EIBA, 1998). The European Installation Bus Association (EIBA) in Brussels centrally advances and distributes the EIB software tools.

15.2.2 Local operating network (LON) bus

LON means local operating network. It was created to serve as a common, universal tool in decentralized automation systems. This technology is used for several applications, including process

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Source: J. Reiss, Fraunhofer Institut für Bauphysik, Stuttgart

Figure 15.2.6 Configuration of an area line automation, machinery control systems, aircraft, ships or telecommunications. Another major area of application is building automation systems (particularly in functional buildings). The LON technology is based on the LON works technology. A neuron chip, which is produced under licence by Motorola and Toshiba, is the 'heart' of this technology. This programmable processor facilitates an intelligent processing of the data and is provided with an efficient communication interface for data exchange with other appliances. The components of a LON comprise controllers, sensors, actuators and system components, communicating via a two-wire line. The intelligence is distributed to the individual components (nodes), so it is decentralized. This makes the system rather resistant to disturbances and failures. If one component fails, the remaining system may continue to operate unaffectedly, with only this one component missing (Harke, 2004).

The LON bus is primarily used in medium- and large-scale industrial buildings. In residential buildings and small-scale functional buildings, the EIB bus is more popular.

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