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

HVAC Control in the New Millenniumstatistical signal and ranges of signal acceptance. Violation of thosespecifications means that the network could function poorly. Exceededsegment lengths, drop cable lengths, twisted-pair connections, substitutingThinnet for standard cable segments or inserting twisted-pairs allstress the network.Some Ethernet versions have data encoding differences. The OSImodel has become generally accepted due to the globalization of telecommunicationsand data communications. It is a de facto standard.True standardization implies comprehensive testing for conformity toOSI and this is a major undertaking in the future.Wireless EthernetBaseband wireless networks use infrared or radio frequency signaltransmission to transmit signals through the air and through the walls.Spread-spectrum technology (SST) uses multiple frequencies and carriesa single baseband channel. The only difference between the more traditionalcable networks and a wireless network is the lack of media. Noconnecting wires are used.This technology is useful for buildings where adding wiring wouldbe costly. This includes old buildings without conduits, hollow walls, orfalse ceilings, or buildings with an asbestos problem.Infrared technology is not advisable for dusty, dirty, or smokyenvironments because these particles degrade the signals. Infrared technologyis also limited by line-of-sight installations.The hardware required for the most minimal configuration isnode-based wireless transmitters which eliminates the need for anynetwork cabling. The more usual configuration uses a backbone cable orwire that interconnects the nodes. The cable or wire is either coaxialcable, twisted-pair wire bundles and telephone modular jumpers, oroptical fiber.Coaxial cable is most often designated as RG-50, RG-59, or RG-225coaxial cable. The 50-ohm cable (RG-50) performs better than 75-ohmCATV cable (RG-59 or RG-225) because it has better resistance to lowfrequencyelectromagnetic noise which means that it shields the signaland is rarely affected by external interference. Thinnet and Cheapernetare 75-ohm cable and can suffer this interference.Unshielded twisted-pair (UTP) Ethernet wire is designated as ei-©2001 by The Fairmont Press, Inc. All rights reserved.