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

HVAC Control in the New MillenniumBroadband cables are most often used for analog communications,but optical fiber broadband is used to transmit digital transmissions aswell.Broadband networks provide more bandwidth, higher speeds anda larger geographic service than baseband networks, but the cost ishigher. The physical medium and transmission differ from baseband butthe Ethernet protocols can transmit on baseband and interconnect usinga bridge.Broadband can simultaneously carry voice, data, video or anyother digital or analog traffic at different frequencies. When broadbandnetworks carry voice, video, and data communication signals concurrentlyon the same networks, a bridging mechanism is required to transmitdata between networks using different transmission media. Broadbanddisadvantages include its initial expense as well as the difficultyand expense in moving or adding nodes to expand the network.The main difference between a standard Ethernet, twisted-pair,and the Cheapernet and Thinnet variations is the maximum length ofcable each version supports and the minimum distance between nodes.Standard Ethernet supports a maximum 500-meter segment andnodes spaced no closer than 2.5 meters, while Cheapernet and Thinnetrun on thinner 75-ohm cabling and support a maximum 200 meter segment.The nodes can be spaced as close as 0.5 meter. The 50-ohm coaxialcable is physically thicker and stronger, better shielded, and more expensivethan the 75-ohm Thinnet cable. Broadband uses a televisiontuner-like modem that converts each channel to a separate frequency.There can be 2 to 80 channels per broadband cable. BroadbandEthernet can run for longer distances than baseband, up to 2 km. Opticalfiber technology is newer and provides greater bandwidth and highertransmission speeds than broadband coaxial cable, but it is more expensive.Fiber cable is more difficult to splice and repair. Expansion andcontraction from extremes of heat and cold can fracture the cable. Heatand cold can also affect the optical qualities and gradually decrease thebandwidth.Optical fiber transmission is available through PC adapter boardsfor Ethernet. Optical fiber networks have some of the same transmissioncharacteristics as broadband cable but they are more expensive andmore difficult to debug, maintain, and expand. They are not susceptibleto electronic noise or signal crosstalk and provide good security.©2001 by The Fairmont Press, Inc. All rights reserved.