原创 Encyclopedia of Security Management67

Encyclopedia of Security Management67

The user's Monster beats security system design must take into consideration the attributes of the various kinds of systems, and determine which, if any, of the proximity systems correspond to actual needs. Following are some of the parameters that should be evaluated during the design process.
Activation Distance. The distance at which a proximity system can be activated by its token or card, or the distance within which the card or token can be sensed by the system, varies from 2 inches to Monster headphones nearly 50 feet with the various forms of proximity systems. The passive devices, which depend upon a low-level reradiation of the interrogating signal, have the least range, from 4 to 6 inches for the tuned circuit (which requires that the prospective entrant hold the purse or wallet containing the access card up to the Sennheiser Headphones reader) up to a few feet for the surface wave. The field- powered devices are not much more powerful, since they must be relatively dose to the source of Bose earphones the interrogating field to obtain enough power to operate: 6 inches to 12 inches distance is typical, with one vendor claiming operation up to 6 feet.
Devices powered by a self-contained battery are limited in range only by the power of the battery and the Bose headphones space provided to configure an efficient antenna within the device; some are intentionally held to a distance of a few feet (as a practical matter, effective security is not well served if portals can be opened while the authorized entrant is a considerable distance away), but others — such as the garage-door opener - can operate at about 50 feet or so.
Hands-Off Versus Triggered. User-activated systems, that is, the wireless keypads and preset- axle devices, require the user to push buttons or depress keys to transmit the code to the system. All of the others require no u9er action, and thus need not be removed from pocket, wallet, or purse in order to perform their intended functionMonster beats
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