| HTINews Article - Jun98 - [HTI Home Page] |
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INTERNATIONAL MODEL OF A
LIGHTING CONTROL SYSTEM
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Dr. Kenneth Wacks provides management and engineering consulting in home and building automation to utilities and manufacturers world-wide. He offers impartial and practical advice on business opportunities, network alternatives, and product development. The EIA (Electronic Industries Association) has appointed him chairman of the committee establishing international home and building automation standards. He is the author of "Home Automation and Utility Customer Services," published by Cutter Information Corp. . For further information, please contact Ken at 9 Pinewood Road, Stoneham, Massachusetts 02180, USA; Tel: (781) 662-6211, Fax: (781) 665-4311, E-mail: kenn@alum.mit.edu . |
The Importance of Application Models
A key feature of home automation systems is the new services possible through the interaction of appliances, sensors, switches, and user controls. A communications network with a uniform protocol enables products to work cooperatively. However, the designers of appliances and subsystems also need common system models so products from various manufacturers can interoperate. Decisions about functions and variables that are accessible from other devices on a home automation network must be consistent among the devices.
An application model describes the engineering aspects of a device that can be read, written, or executed via a home automation network. A model is essential for conveying this information to manufacturers of products that will be linked by a home automation network.
No major protocol includes complete application models of subsystems in the specifications. Therefore, the international committee called Home Electronic System (HES), writing standards for home automation, is tackling this problem. (Please see the April 1998 issue of HTINews for an overview of international standards.) The committee has approved U.S.-developed system models for lighting control, energy management, security, and HVAC (heating, ventilating, and air-conditioning).
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A lighting control system is represented by a collection of lighting fixtures containing lamps and devices for controlling these fixtures remotely. Parameters that can be controlled include on/off, light level, light color, focus, aperture, position in space, orientation, and timing parameters for changes of state. This model describes a complex fixture. A typical fixture contains a subset of these features. The following control devices are accommodated in the model:
- Switch
- Dimmer
- Sensors: room occupancy, lighting intensity
- User interface
- Lighting system controller
A very simple lighting system may not need a controller. The switches and dimmers would be wired directly to the fixtures. Each component contains an HES interface or is connected to a concentrator that provides an HES interface for a group of similar devices. The concentrator accommodates low cost devices. Figure 1 illustrates a collection of physical devices constituting an HES lighting system.
Figure 1. Example of Physical Components in an HES Lighting System
A logical model is required to organize the lighting system components for cooperative operation. The basic premise for the operation of a home automation lighting system is actuation of lamps remotely. Lamp actuation may be accomplished by a simple switch or dimmer, or by a complex scene programmed into a controller. The controller may provide synchronization and sequencing among numerous fixtures. Depending on the intelligence in the fixtures, the controller may actuate each change of lighting state or may set high level parameters into an intelligent fixture. To accommodate this range of sophistication in a lighting system, logical models were proposed for a very simple HES lighting system, a complex HES lighting system, and a hierarchically arranged HES lighting system.
A new logical element, the lighting activator is introduced to simplify the logical model. The lighting activator represents a source of signals that control at least one fixture remotely. An activator may be embodied physically in a simple device that generates on and off signals, such as a switch or a sensor. A lighting activator could be a hand-held unit with an infrared link that generates HES messages. For complex lighting systems, the lighting activator may actually be implemented in a microprocessor-based controller. For logical consistency, another element is introduced. The illuminator represents a source of light and is typically a physical fixture that includes one or more lamps that may be controlled individually.
A simple HES lighting system contains one illuminator and a simple lighting activator, as in Figure 2. The simple lighting activator would be physically a switch or remote control unit. The fixture may or may not be intelligent.
Figure 2. Logical Model of a Simple HES Lighting System
For complex lighting systems, the lighting activator may contain a microprocessor-based controller programmed with a lighting control algorithm. As shown in Figure 3, the user interfaces, switches, dimmers, and sensors may be remotely located and linked by the home control system to the activator. The user interface in the logical model might represent a video terminal for configuring the system while multiple room switches operate various lighting zones.
Links to other subsystems
The logical linkage from the activator to other HES controllers, as shown in Figure 3, provides communications among home control subsystems. For example, a security subsystem controller might send a message to the lighting activator upon detection of an intrusion in a particular room. The lights could be illuminated there to scare an intruder. Responsibility for lighting control remains with the activator. The security controller does not turn on the lights directly, but requests appropriate action by the lighting activator. This prevents contention for system resources. Note that in some implementations, a direct connection to the lights may be required by safety codes.
Figure 3. Logical Model of a Complex HES Lighting System
An HES lighting system with multiple lighting activators may be arranged in a hierarchy. Separate activators might be responsible for different sections of the house or different lighting applications, with a coordinating controller in charge of the entire system. This arrangement is shown in Figure 4. The lighting coordinator may contain external user interfaces. Note that the coordinator does not control any illuminators directly, but issues commands to the lighting activators, which send messages to the illuminators.
Figure 4. Logical Model of a Hierarchical HES Lighting System
In Figure 3, the activator contains a possible connection to other home control subsystems. In a hierarchical arrangement, the lighting coordinator would include this connection. Thus, the coordinator is the point of contact with other subsystems.
This hierarchical model may include more than the two levels shown. (Some commercial lighting systems may be modeled by a hierarchy of four levels.) Note that a logical hierarchical arrangement does not imply a similar physical arrangement. A flat physical configuration may be organized into a logical lighting control system.
Achieving Product Interoperability
The growth of the home automation market requires a variety of products that can work together. Designing to a common model is necessary for interoperability without limiting product differentiation. For example, manufacturers could offer a line of lighting controllers ranging from wall-switches, to hand-held remote controllers, to voice activated units, to software for control from a personal computer.
Interoperability assures the consumer a choice of control methods with fixtures already installed. This promotes market growth for add-on features. The consumer might initially wire the house for a lighting control system using simple fixtures and control devices. Later, as needs and budgets allow, the system could be upgraded for extra features. Thus, both consumers and manufacturers win by supporting interoperability derived from a common application model.
©Copyright 1998, Kenneth P. Wacks
