HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Building Automation, Wireless Technology and the Internetpower transmitters and receivers. RF signals make up a portion of theelectromagnetic spectrum and are used in local-area RF and wide-areaRF implementations.RF transceivers and infrared devices are used to create wirelessLANs, which can connect PCs on a peer-to-peer network or connect anode to a LAN. The range for local-area RF equipment starts from 30feet to about 100 yards and some equipment can reach 600 feet to 1/4mile (1,200 feet). Most local-area RF equipment operates in the Industrial,Scientific, and Medical (ISM) bands, which covers radio frequenciesthat do not require a broadcasting license. The equipment mustmeet certain power and bandwidth restrictions enforced by the FCC(Federal Communication Commission).Most wireless LAN equipment falls into two categories: low-speeddevices, which range from about 115 kilobits per second (Kbps) to 250Kbps and the high-speed devices that transfer data at 1.25 megabytesper second (10 megabits) or greater, which is about the same speed asEthernet.Some wireless connections involve RF transceivers that you attachto the serial port on the PCs. These devices transfer data at the rate ofthe serial port within about a 10-meter range. These small card-sizedtransceivers can transfer files between a desktop PC and notebook PC.They form a two-node network in which one machine, typically theportable device, can access resources available to the other unit, such asa printer.Infrared transceivers also clip on to a serial port and can transferdata between ports. This allows the infrared link on any portable systemto exchange files with other computers or to access its resources. Thereare also versions that attach to a printer, letting you send files to theprinter via infrared technology. Complete wireless-LANs are availablefrom companies such as NCR.The NCR WaveLAN PCMCIA network adapter card fits into themobile user’s notebook, then sends and receives RF signals from a networkbridge which is connected to the LAN server. PCMCIA stands forthe Personal Computer Memory Card International Association. Thisindustry group determines the standards for all credit card-size peripherals,including modems.A key issue in wireless LANs is security. Most wireless LANs radiatetheir information in a nonencrypted format, so sensitive informationis vulnerable. Encryption should be widely used in the future.©2001 by The Fairmont Press, Inc. All rights reserved.