The Constituents of a Security System

Transcription

1 KEN WCK' PERPECTIVE The Constituents of a ecurity In the article The Basics of a ecurity I introduced a new international model of a security system for home and building automation. This model is part of the Home Electronic, an international standard under development by the member nations of the IO and IEC (International Organization for tandardization and International Electrotechnical Commission). s explained in the prior article, this model extends applications of a security system beyond intrusion detection to include activity monitoring for the elderly and latch-key children, duress notification, and safety monitoring. afety is especially important for commercial customers needing quick notification about environmental pollutants, water leaks, unusual temperature variations, and machinery failures. The concepts of zones and partitions, discussed in the previous article, are traditional in security systems. However, these terms are generalized in the security model to accommodate modern busstructured networks. We now delve further into the security model by exploring the following topics: ensor varieties and technologies Control panels and user interfaces controllers larm devices The physical and logical arrangements of these constituents are illustrated. lso, the possible interaction of a security system with other home automation systems is described. ensors The security model accommodates a range of sensors being market and planned. mong these are: Contact sensor: a switch trips if a door or window is opened. contact sensor may be placed below a mat so it is tripped by someone walking across the mat. coustic sensor (also called a shock sensor): a sensor attached to a window is tripped by the sound of breaking glass. -1- Glass break sensor: a conductive foil used commercially near the edge of a glass pane. If the glass break cuts the foil, a current flow is interrupted indicating a problem to the controller. Motion detector: an infrared device detects temperature changes caused by a person passing across a cone-shaped field in front of the detector. Pick-up coil: an electrical coil buried in a driveway detects large metal objects passing, specifically a car. Photo-electric cell: a photocell detects the interruption of light (visible or infrared) from a source. The photocell is installed at a position where a passing person would interrupt the light. moke detector: the common varieties are photo-electric cell, to detect smoke particles, and ionization, to detect smoke. Heat detector: a sensor that trips upon a prewired or programmed rise in temperature. Water detector: usually placed on the floor to sense flooding. Gas detector: may monitor carbon monoxide, carbon dioxide, or oxides of nitrogen. ome of the sensors listed may be offered with various levels of complexity. For example, there are now dual-tech sensors. Conventional passive infrared sensors can only sense movement tangential to the detector. By contrast, devices using Doppler-shift techniques detect motion towards and away from the detector. Combining passive infrared and, Doppler techniques in a single device and processing the resulting signals provides a good way of improving the discrimination of sensors. ome sensors may be programmable to adjust sensitivity levels and timing characteristics according to the application. lthough some of this processing could be done by the controller, the low cost of electronics frequently permits a considerable degree of signal processing to be done within the sensor.

2 Control Panels (User Interface) ecurity system control panels are available in many formats: Wall-mounted keypad Typically, this is a numeric key-pad. dditional keys may be provided for special functions. mong these functions are enabling or disabling sensors in a particular zone and selecting the operating mode of the system. ome panels include separate keys for each function. Others require a special sequence of function and numeric keys. The keying procedure affects user convenience and product cost. This model makes no valuejudgment on these market issues. Keypad with voice response Confirmation of user selection at a keypad may be done by a tone, a sequence of tones, or a spoken voice drawn from a synthesized or pre-recorded vocabulary. Computer keyboard few security systems can now be programmed from a personal computer. The system configuration may be entered at the computer and down-loaded into the security controller. nother controller It is possible to program a home automation controller responsible for a different application system (for example, energy management) to set operating parameters in the security system. s security system controller is responsible for: Configuring the sensors into zones and partitions Communicating with the user via control panels Establishing an operating mode for each partition Monitoring the sensors Issuing the appropriate notification or alarms -2- Establishing a telephone or radio link to a monitoring station Monitoring sensor and system integrity Miscellaneous network management and testing Communicating with other home automation controllers Varieties of controllers include: pecialized computer with embedded microcode Personal computer The computer must be kept running all the time to monitor the security sensors and issue alerts according the security mode selected. Fully distributed controller It is possible, though not common, to distribute the functions of a controller among the other elements of security system (sensors, control panels, and alarms). In this case, the controller is a virtual function, not a physical component. The physical model presented here is based on the usual practice of designing a physical controller for a security system. larms ecurity system alarms may include: siren or bells telephone or radio call to a monitoring service or to a specified list of persons The type of alarm depends on the situation requiring notification. s noted in the previous article, this security model may apply to: Intrusion Notification about elderly or latch-key child Medical emergency Panic alarm Forced disarm Fire Gas detection Water leak Temperature extreme Earthquake

3 Machinery failure trouble The Physical Model of a ecurity The physical elements of the international Home Electronic (HE) security system model are shown in Figure 1. key decision for manufacturers is whether the HE network forms the basis for linking together the security components. Choices include: - Fully HE compatible Every sensor, every alarm, and the controller contain an HE interface. - Partial HE compatible group of sensors or alarms shares a network concentrator. The concentrator includes the HE interface. The concentrators and the controller comprise the HE network. - Isolated network Only the security controller contains an HE interface. The sensors link to the controller via a proprietary network. The communications network interconnecting most security system components sold now is proprietary. ecurity manufacturers are concerned that connections to other systems via a common network will degrade reliability. Most security systems are designed as isolated networks because of concerns for system integrity. Thus, Figure 2 is a physical model according to current practice. In fact, an HE security network could be isolated from all other networks via appropriate choices of private messages or physical devices that isolate subnetworks, each of which uses HE. The security controller may be on a separate bus joined to other home automation applications via a communications router. The router is interposed to provide electrical isolation for an auxiliary power source, such as a battery, supplying part or all of the security system if the mains fail. Power isolation might be limited to critical portions of the security systems. It may not be economical to maintain all sensors active during a power failure. For example, in a mains failure, only the peripheral sensors might be batterybacked to manage the cost of auxiliary power, while the motion detectors would lose power. -3- The Logical Model of a ecurity The logical relationship among these components is illustrated in Figure 3. If the physical model of Figure 2 is implemented, the controller may make the attached components logically visible to the HE network, so Figure 3 still applies. The telephone connection is included because some alarms are issued by calling a preprogrammed telephone number and annunciating the alarm, or using the telephone to report a latch-key child. radio link could substitute for or back up the telephone. Linking ecurity into Home utomation ecurity is one of many application systems possible in a home control network. s shown in Figure 3, the security controller may be linked to other home control systems or to a home coordinator. The coordinator might be responsible for providing common scheduling and interaction among applications. This coordination function may be distributed among the system controllers through sophisticated software, thereby eliminating a separate coordinating controller. The Complete ecurity Model The security system model was successfully balloted by the IO/IEC member countries last year and is being prepared for publication. The complete document includes a section describing messages that are exchanged among the system components: ensors Zone Control Zone Control Partition Control Partition Control larm Partition Control External (nother controller or control panel) National standards bodies and consortia working in home and building automation are urged to adopt this and related application models. ll the models that comprise the Home Electronic standard are generic. This means they apply broadly, can be adapted narrowly, and do not preclude innovative product features. Thus, adopting generic models conserves engineering resources while providing maximum marketing flexibility to position products as unique and worthy of substantial profit margins. Copyright 2007, Kenneth P. Wacks Dr. Kenneth Wacks provides management and engi-

4 neering 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 EI (Electronic Industries lliance) has appointed him chair of the committee establishing international home and building automation standards. For further information, please contact Ken at 9 Pinewood Road, toneham, Massachusetts 02180, U; Tel: (781) , Fax: (781) , [email protected]. -4-

5 =larm, Telephone, Radio C=Control Panel =ensor =HE Interface ecurity C C Home Control Medium Other Figure 1. Physical HE ecurity Model -5-

6 =larm, Telephone, Radio C=Control Panel =ensor =HE Interface C ecurity C Home Control Medium Other Figure 2. Physical HE ecurity Model with Isolated Components Control Panel ensor ensor ensor ecurity larm Telephone Radio Links to other systems or to a home coordinator -6-

7 Figure 3. Logical Model for HE ecurity -7-