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Fig. 2: Principle of Manchester Encoding The limits of wiring Wiring effort for more complex use cases as well as limited flexibility to adapt to changing requirements limits the use of simple 0–10V control. To illustrate the point, consider a simple scenario of four lights being controlled via 0–10V. There are two options for doing so – see figure 1. * You can connect all of them to the same bus and accept that all will have the same light intensity. This will result in simplified wiring and requires only a simple controller. * You can connect each of them individually to a multi-channel 0–10V controller in order to set individual light levels. This will require more complex wiring and a more powerful controller. From this, it becomes clear that wiring complexity grows significantly once the system is required to control a set of lights together. Furthermore, an upgrade from a simple scenario (on the left) to an advanced control (on the right) cannot be realised without costly changes of the existing wiring and the controller. In addition, there is no provision for a feedback channel and it is almost impossible to include sensors, for example, for occupancy detection, to achieve optimal energy saving rates. These disadvantages combined lead to 0–10V control being used predominantly in simpler installations where advanced features are not required. Smart wired lighting control In contrast to 0–10V/1–10V, DALI lighting control based on a digital protocol can address complex scenarios. The basic idea is to connect a number of devices onto a bidirectional data bus and identify individual devices by means of unique device addresses. These devices can then individually receive control commands and even respond with a status update. From a technology perspective, DALI is a serial protocol based on a two-wire bus using the following parameters: * Asynchronous – there is no dedicated clock line (wire) * Half-duplex – at any time, you can either send data or receive data, but not both * Data rate of 1200 Bit per second based on Manchester Encoding – see figure 2 – the clock is encoded as part of the data stream. Note the encoding of the Bits as rising and falling edges of the data line. Only the data signal is actually transmitted, the clock signal is shown here for reference only. In a DALI system, one control device can communicate with up to 64 control gears. These 64 control gears can either be addressed individually, as part of a group (up to 16 groups can be defined) or altogether via a broadcast. This group and broadcast mechanisms address one key limitation of the low Bit rate, which reduces the available system bandwidth and potentially increases latency in situation where many command exchanges need to take place (for example, to switch on a large number of lights simultaneously). In addition, up to 16 light scenes can be defined for tailored lighting. These characteristics make DALI well suited for wired lighting control where advanced control is required. Wired versus wireless Several standards exist for wired communication between light sensors and controlling devices such as switches. They enable advanced control scenarios while providing reliable communication at the same time. However, in retrofit projects, the installation of wired control can be complex, costly and timeconsuming. Modernising an existing building with wired control systems requires the addition of dedicated control cabling to each individual lamp. Each element, such as switches, sensors, lights, in these systems requires dedicated cabling. ISO9001:2008 www.norsun.com.tw For more information please contact gwenlin@norsun.com.tw directly www.electronics-eetimes.com Electronic Engineering Times Europe September 2014 23


EETE SEP 2014
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