Digital control entails using digital communication architecture to network intelligent lighting control devices. It enables more economical integration of multiple control strategies, while being flexible and capable of generating feedback.
The building block of analog 0–10-volt wiring is two wires with a 1–10V potential between them; control commands are based on simple variations in voltage. Digital wiring uses two wires with a maximum potential of 18V between them; however, control commands and other information are transmitted as digital binary messages (ones and zeroes), with very little current drawn through the wires, when compared to an analog signal. Communication goes both ways, allowing networked control devices to provide useful feedback, such as real-time performance data for energy analysis and maintenance.
When using analog devices, each shared function requires its own wire, resulting in the potential for a high number of low-voltage wires with associated risks of miswiring when building sophisticated control systems. Digital wiring uses a single bus to connect all control devices, resulting in a more elegant wiring configuration and reduced installation costs. If intelligent devices are used in a distributed control scheme, centrally located equipment, such as lighting control panels, may be eliminated. Digital may be a different animal from what many electrical workers are used to, but it can be simpler and less prone to error to install, particularly in complex control applications.
A defining characteristic of digital control is that its wiring solutions use soft configuration schemes, such as programming, to replace termination-based configurations where wires land on specific terminals to enable functions. For example, different control devices can be integrated easily, enabling the combination of multiple-control strategies and greater control capabilities without adding significant cost.
As with analog systems, devices communicating across digital control wiring must share a common protocol. Popular standard protocols include Digital Addressable Lighting Interface (DALI), RS-485, LON, Ethernet and BACnet. Some manufacturers have developed proprietary protocols that are unique to a single company or are open, such as Digital Serial Interface, DALI’s precursor.
Each protocol offers different capabilities in terms of topology (wiring configuration), transferability of signal (maximum length of wiring run without the use of a repeater or other supporting devices), and sensitivity to polarity.
RS-485 is based on shielded twisted-pair small-gauge wiring and allows networks to run up to 4,000 feet without repeaters, but this type of wiring is polarity-sensitive and requires a linear topology. LON uses unshielded twisted-pair, enabling an open topology, but wiring runs are limited to 1,500 feet before a repeater is required.
DALI promised an open standard for digital lighting control and a dramatic expansion of capabilities, such as individual addressable ballast control, open topology, polarity-free wiring, long wiring runs, and the ability to zone and rezone fixtures using software, without rewiring. Depending on the manufacturer, the digital wiring can be installed as Class 1 or Class 2 wiring. However, the standard has suffered from complex commissioning requirements, lack of definition for communication between controls and relatively slow transmission speed.
As a result, a growing number of manufacturers offer packaged proprietary-protocol systems, in some cases based on DALI. These systems mitigate some of the disadvantages within an engineered solution. The primary tradeoff is that, once installed, the owner is tied to a single manufacturer for technical support and downstream component replacement. Additionally, no two systems are exactly the same, even though their equipment may perform similar functions. Therefore, you must always follow manufacturer wiring requirements for installation.
In some of these systems, the point of control is a digital dimming ballast, while in others, it is distributed relays residing in power packs and occupancy sensors. Some relay-based digital systems allow individual fixture control and control of analog dimming ballasts. These systems often feature preterminated wires and plug-and-play devices, enabling simple installation and, in some cases, remote and self-commissioning.
Enhanced capabilities imply a higher cost, but for more sophisticated control systems, digital can be quite cost-effective. The advanced circuitry of intelligent control devices and use of preinstalled connectors will impose a cost premium on the project, but eliminating central equipment and simplified wiring may produce significant installation savings. Capabilities and associated cost must be appropriately matched to the application. In some buildings, digital and analog systems may be installed in different spaces and can be tied together using a gateway, if needed.
Thanks to Andrew Parker, Encelium Technologies; Thomas Hinds, Lutron Electronics Co.; Ronald Bryce, PLC-Multipoint; Greg Bennorth, Universal Lighting Technologies; and Pete Baselici and Eric Fournier, Legrand/WattStopper, for their contributions.
DILOUIE, a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.