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- February 2005 -
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What is the LCN Installation Bus?
There are 3 significant universal installation buses worldwide: the EIB, LON and LCN. In this article we describe the LCN installation bus that distinguishes itself through performance and cost effectiveness compared to the rest.
In order to understand what LCN installation bus is, let's first look at the conventional electrical wiring method in a building. In this method, a switch or a button is wired to directly effect the power supply to a consumer (lights, motors, fixtures). The switch or a button mechanically cut or connect power to the consumer. Therefore, in the simplest case, the switch is wired directly to the consumer. In more complicated case like 3-way or 4-way wiring, a lot more cable is needed to connect the switches and the consumer.
Besides requiring lot of cable for basic functions, the disadvantages in the conventional wiring as such is that the established functions can not be changed without having to rewire the installation. For example, to add a new switch to a light, new cable must connect the new switch to the existing one and the connection from the existing to the light must be rewired. Additionally, when dealing with peripherals and accessories such sensors, each one is connected to and is used only by one device. For example, an occupancy sensor wired to the light switch to save electricity when no one is in the room can not be shared with the alarm system. The alarm system has its own motion detector. The result is that it is very costly to add new functionalities to the existing wiring.
The installation bus is a new way to electrically wire buildings that is more cost effective and offers many new functionalities over the conventional method. There are 3 significant universal installation buses worldwide: the EIB, LON and LCN. In this article we describe the LCN installation bus that distinguishes itself through performance and cost effectiveness compared to the rest.
In the LCN installation bus, an extra wire in the standard electrical cable is used as the "bus". This design makes it easy for ordinary electricians to handle the installation because no special purpose cable is required, just like in the conventional installation. All electrical consumers are connected to the intelligent modules that are installed on the electrical cable and act as intelligent nodes in the LCN network. These intelligent nodes are small enough to fit into wall boxes where consumers are also installed. Switches and other peripherals like sensors are also connected to any intelligent nodes in the network at convenience because they are shared by the consumers. The immediate effect is that the wiring is reduced to the essential, eg. only to the consumers, and is clearly arranged in such a way that problems or failures can be located quickly. Furthermore, the advantage of the LCN installation bus is that the functionalities can be reconfigured any time and expansion of the bus is is just as easy as extending the power line.
Some readers would ask : "Why not connect the bus modules wirelessly to save the extra wire in the electrical cable?" The answer is simple, wireless technologies, no matter how they are sold to the public, are not reliable in building automation. This is due to the facts that there are too many static and dynamic factors at the installation sites affecting the wireless performance.
Other readers also ask: "Why not use the power lines to transmit the bus signals?". Here the answer is also similar, power line carrier technology has not proven to be reliable. There are many efforts to get these two technologies to become somewhat more reliable, however, these measures are costly and can never reach the 100% reliability of the plain old electrical wire. By the way, in retrofitting projects, the LCN bus wire just needs physically to be a low voltage thin wire connecting the bus modules. The thick and strong electrical wire used in new construction is just for convenient purpose. Electrically the bus signals are at 30V max level.
How does LCN Installation Bus work?
Each of the intelligent module, called "bus module", is equipped with a microprocessor and can perform pre-programmed functions in stand-alone mode (eg. without having to connect to any other module). Bus modules have power outputs to drive electrical loads (dimmable) and have sensor inputs to connect to a large variety plug-and-play sensors. They also have inputs for switches, IR receiver, binary signals, etc. The power supply is taken from the power line cable directly therefore no extra power supply unit is needed. The art of miniaturization is so good that the standard module, the LCN-UPP, fits into the wall box behind the switch or receptacle mechanic. Once installed, each unit automatically locates other modules on the bus line to automatically form a mesh network. The communication between these intelligent modules happens on the extra wire in the power line cable as previously mentioned. The bus modules exchange messages, called "telegrams", with each other. The telegrams are structured digital codes that contain information such as the source, destination command and status.
LCN Simplified Telegram
The LCN communication protocol is simple (for speed reason) yet sophisticated (prioritizing, grouping, broadcasting) thus allowing the whole network to function reliably as if it were a single sophisticated whole building control module. Although the speed of the communication is 9600 bauds, the effectiveness of the design allows real-time handling of commands sent from one module to the other even when they are physically far apart from each other. The reliability in the system also comes from the fact that the LCN communication protocol requires two-way communication between modules. Any command going from one module to the other requires an acknowledgment in return that the command has been successfully executed. This ensures the integrity of the system.
The LCN installation can grow from a single module system to a max. 30.000 addressable module system by just adding new modules to the power line. However the 30.000 bus modules can not be put on a single bus line. This number is infinitely large considering that a 3-bedroom house would need only about 5-8 units for most of the lighting and control tasks in the house. A single bus line can accommodate up to 250 addressable bus modules and is called "segment". In a large construction project this could make up one story or a wing or a building in a complex. Segments are connected together by segment-couplers.
The LCN protocol identifies the source and destination bus modules by their address and by the segment that it is in. By design, the installation is divided into logical circuitries by the installers making the layout easy to understand by electricians who are used to splitting the electrical cable at the service entry of the building into circuits controlling by circuit breakers. As mentioned, segment couplers are only needed in a large mansions (such as Mr. Bill Gates home) or several story high rise buildings or several buildings in a large commercial complex.
One of the characteristics of LCN installation bus is that there are only few basic bus modules to choose from that, however, are accompanied by a large number of peripherals, sensors, load drivers, relays, adaptors, etc.. This combination makes the design, planning and installation of the system simple but very flexible. Peripherals attached to one bus module on the LCN network can be shared be any other module over the net. This sharing practically makes the whole installation appear to have more sensors and peripherals than it really does. For example, the outside temperature sensor can be shared by the unit that control the air conditioning system and the unit that operate windows to allow natural air flow to circulate in the building. Or the window open sensor can be shared by the alarm system and the unit that operates the air conditioner. The system works more effectively and can react better to both local and global events.
Integration of controlling task to one system
The LCN installation bus physically ties all single modules installed throughout the building together to act like one giant single module with a large number of inputs/outputs that control the whole building. The main piece that glues the functionalities together is the software that programs the individual modules to interconnect with each other. After the physical installation is completed, the subsequent programming task utilizes a software called LCN-PRO running on a PC that taps anywhere onto the bus via a module called LCN-PC. The software automatically allocates all bus modules and their peripherals on the bus. Most of the basic programming tasks are just point and click and none requires a computer programming skill as the goal of LCN is to enable ordinary trained electricians to completely handle all stages from planning, installation to programming of the finished installation. The programming capabilities are simple to master yet flexible and sophisticated. For example, some of the switches and push buttons can just be programmed to be programmed by the users (home owners, office occupants, etc.) themselves later. Users can store/recall/change complex "scenes" that they create at will. Once the system programming task is completed, a binary program file is saved and kept by the electrician. Replacement units can just be quickly programmed by uploading binary code to the targets. There is no need to go through all programming steps as with a new installation. A fully programmed installation operates autonomously without a central controller, the PC is only needed for the programming process.
Operation and Maintenance
Due to the fact that there is no central controller in the middle of all the actions, the system operates much more reliable. Failure of any bus module (guaranteed by the manufacturer to last min. 45 years) leads only to local failure or anything connected to it. Most of the time, overload is automatically detected and prevented by the firmware in the modules, long before any catastrophic failure can occur. Locating the failed unit is as easy as locating a failed switch for electricians. In contrast, failure in the central controller of other building automation systems will lead to widespread building control problem that are difficult to diagnose. The LCN installation system remains virtually maintenance free once it is in operation.
Recovery from total power failure
LCN bus modules are designed to bridge a power failure upto 20 sec without loosing track of what it is currently doing. This capability helps the LCN system to be resistant to problems caused by power line surges (electrical motors, capacitive loads, weather related effects) that plague other building control system if not suppressed with extra equipments. And when it comes to recovery from a total power failure event, a distributed mesh network of controllers is superior over centrally controlled system. Each of LCN bus module boots up quickly when the power is restored and the whole building is back functioning after few seconds. This is compared to a long boot up time of the central computer that then needs sometime to interrogate the status of the building before being able to resume interrupted control tasks.
The cost of the LCN modules, without installation, for a 3-bedroom single family house to cover lighting and other basic functions is between $2,000 to $3,000. Adding a keyless entry system will cost a little bit more. The pay off of this initial investment are years of convenient/comfort living and energy cost saving.