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

HVAC Control in the New MillenniumFigure 8-1. Network hierarchy.control devices including PCs and distributed control systems (DCSs)(Figure 8-2). It is used at the level directly below fieldbus and devicelevelnetwork systems. It transmits control and device data, configuresthe system architecture, powers the devices, and monitors thenetwork.AS-i can be used for upgrading HVAC systems. Parallel controlwiring can be replaced with a simple AS-i cable (Figure 8-3). Mostconventional wiring system can be replaced and users report wiringsavings of up to 40%.Conformance to the AS-i standard assures interoperability. Eachslave that fulfills the standard’s requirements can work together withany other slave in the network.The network uses a common cabling system with all peripheraldevices connected to the AS-i cable. The AS-i protocol is embedded inthe slave chip which connects the sensors and actuators to the cable.AS-i uses one master per network that calls up all the connectedslaves with a cyclic polling that uses their address. The AS-i datapackets are short with simple structures and have a fixed length.Four usable data bits are exchanged between a master and every in-©2001 by The Fairmont Press, Inc. All rights reserved.