Hello DALI

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Without a doubt, plant operations have achieved an unprecedented level of sophistication. Electrical products and energy systems have been imbued with intelligence air compressors have self-contained sensors, pumps monitor their own health, and industrial networks allow plant managers to monitor the entire plant floor from the office.

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Because lighting accounts for as much as 25% of the typical plant's energy cost, it comes as no surprise that lighting technology has evolved in the same direction. Today, plant professionals can have lighting intelligence, flexibility and two-way communication through a system known as DALI.

Tagging ballasts
The Digital Addressable Lighting Interface (DALI) is a communication protocol specifically for lighting systems. This open standard was established in Europe and has been adopted in North America, where mainstream applications are embracing it.

The best way to think about how DALI works is by analogy with a typical suburban subdivision. Consider a street with many driveways branching from it. Each driveway ends at a house, each with a unique address and activities taking place.

Related to DALI, the house represents the ballast, the driveway represents the ballast's connection to the street, and the street is a low-voltage, two-wire control bus. Typically, the control bus also referred to as a loop is powered at 16 VDC. In this imaginary DALI-ville, streets can have as many as 64 houses connected to them.

A signal emanating from a control point operates the ballast. This controller may be a computer, wallbox device or sensor. Establishing a communication link requires each ballast to have its own address. A PC or wallbox scene controller sends a command to the ballasts and any other DALI device on the loop to randomly address itself with a 24-bit long-form address (enabling more than 16 million possibilities). The PC or wallbox then randomly assigns a simplified short-form address to each long address in numerical order from 1 to 64 (see Figure 1).

Just as each house has its own individuality, so does each ballast, and the memory residing in a ballast may be modified, or painted, to meet the needs of the space occupant. For example, the resident in office No. 1 can have the lights set at 75% output and the resident of office No. 2 can set output at 50%, while the adjacent manufacturing cell selects 100% light output. Although these fixtures are connected to the same power circuit, DALI establishes lighting control circuits that are independent of power circuits.

The system's brains reside in the ballast, not in a control panel, where it would take up valuable space at a remote location. The controller sends a DALI signal onto the loop. The control signal might order the ballasts to run program 3, at which point each ballast recalls program 3 from its memory and responds accordingly. The response could be anything from 'turn on'to 'turn off' , 'dim up' , 'dim down' , or another specific command the DALI protocol prescribes.

DALI applies existing digital technology to a new application. Since the early 1990s, DDC controls have been available to the HVAC industry, and the lighting industry caught up to the technology.


Figure 1. Like a subdivision map showing how streets, driveways and houses are connected, this schematic of the DALI network illustrates how ballasts are connected in a logical manner.

At the plant level
DALI offers a lighting system with three previously unavailable characteristics: intelligence, flexibility and two-way communication. Because the ballast now contains software, it is a smart device.

Imagine the convenience of controlling a lighting system from a desktop and the flexibility to relocate fixtures and adjust grouping without having to worry about lighting circuit details. Moreover, two-way communication gives the maintenance engineer up-to-the-minute reports about performance shifts, system faults as well as lamp and ballast failures. When the engineer needs to modify the lighting, a DALI system accommodates moves, adds and changes instantly without costly rewiring. This flexibility makes it easy to adapt lighting to future needs and requirements, customize lighting to space requirements, and evolve the lighting to fit changing use patterns.

Many manufacturing plants switch the lighting at the breaker panel, but many times access to breaker panels is obstructed. Therefore, lights may operate continuously although the plant doesn't. Additionally, even if the panel is easily accessible, switching breakers repeatedly can lead to premature spring failure. Controlling the entire facility's lighting from a computer maximizes both energy and maintenance savings.

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