DALI: General system description

26 10 2011

For the digital interface, specified in the draft of the IEC standard, there are several features, which operate under different principals than the features of the analog interface. Principally the digital interface represents an interface structure for lighting applications that can be enlarged. This new interface does not compete with BMS. The analog interface and the signal level 1–10V allow for a connection of functional units (sensors and actuators) from different illumination electronics manufacturers. The 1–10V interface does not allow an individual addressing. Consequently all units, which are connected to a 1–10V interface,
can be addressed in common only. Furthermore, the lamps luminous flux relation has not been standardized with reference to the interface voltage (light differences). Another disadvantage is the fact that it is impossible to switch off the 1–10V units by means of the interface. To disconnect the units they need to be separated from the mains voltage.

Characteristics and features of the digital interface:

Definition in IEC 60929 – this allows the combination ofunits from different manufacturers. It must be emphasized as a special fact that all manufacturers, who are represented in the AG DALI, have made a joint effort to verify the compliance of their units with this standard to guarantee a high functional security.
Effective data transfer rate (1.200 bits/sek.) – enables an interference-free operation of the system. The physical low-level has been defined with the interface voltage at 0 Volt (- 4.5 Volt to + 4.5 Volt) on the receiver’s side. The high-level condition is represented by the interface voltage of 16 Volt (9.5 Volt to 22.5 Volt) on the receiving side. A maximum voltage decrease of 2 V between sender and receiver is admissible on the leads of the interface.

Safety distance of interference voltage – a safe operation is guaranteed by the large-scale interference voltage distance between the sender and the receiver side.
Data coding – the Manchester-Code has been used here; its structure allows the detection of transmission errors.
Maximum system current – the central interface power supply has been set to allow a maximum current input of 250 mA. Each participant connected to the interface may consume a maximum of 2 mA. This must be taken into consideration for the selection of the power supply interface.

Limited system size – the maximum number of 64 units with an individual address can be distinguished within a system.
Revertive signals of information – e.g. ON/OFF, actual brightness of the connected lamps, lamp state etc. are possible.

Two-wire control lead – two base-isolations should be provided between two leads. A single-threaded isolation of a lead is therefore sufficient.
Control and supply leads can be wired together, make sure to install a minimum lead diameter according to the following table:

Lead length                       Minimum lead diameter
up to100 meters                           0,5 mm2
100 – 150 meters                         0,75 mm2
above 150 meters                        1,5 mm2

The maximum lead length between two connected systems must not exceed 300 meters.
Potentialfree control input – the control input is separated galvanically from the mains voltage. Consequently all system participants may be operated with different outer conductors (phases).
No termination resistors required – it is not necessary to terminate the interface leads with resistors.
Dimming range 0.1 % –100 % – the lower limit depends on the manufacturer. The course of the dimming curve is standardized and adapted to the sensitivity of the eye (logarithmic dimming curve). The impression of a similar
brightness, when electronic ballasts of different manufacturers are used, is a result of the standardization. This requires
however, that the lower limit of the dimming range is equal for all units (e.g. all units show a lower dimming range of 3 %) belonging to the same power class (lamp power).
Programmable dimming times – special adjustments like adjusting light change speeds are possible.
Interruption of the data transfer – fixed light adjustments are interpreted automatically (emergency operation).
Storage of lighting scenes – a storage of up to 16 scenes is possible.
Connection to Building Management Systems by converters – the very first design intent has been to apply the interface in rooms for an integration into BMS by means of converters.
Easy new configuration of the system – Once installed and configurated, a modification of the system function, the illumination scene or the illumination functions is only a question of configuration requiring no modification of the hardware. Example: Regrouping of luminaires into an open-plan office.
Easy integration of new components – new components can be added everywhere within the system whenever an
existing illumination system needs to be enlarged. Consideration should be made that the dimensioning of the
system power supply will be sufficient.


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