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

Computer Networks and SecurityMODBUS protocol could be used for exchanging data.Ethernet interfaces smoothly with device networks such asSeriplex and AS-i (Actuator Sensor Interface), which is used in Europe.Both of these are deterministic, which allows them to maintain controlsequencing and accuracy.Seriplex networks can accommodate up to 7,680 discrete or 480analog I/O points, with up to 300 devices connected to one networkcable of up to 5,000 feet. AS-i can accommodate 31 nodes and up to 248I/O on a 330-foot network or 660 feet with a repeater.Filters can be used to monitor which I/O points report automatically,such as when an emergency stop is needed. The filter can also beused to capture and record data.Advancements in fieldbus technology are having a major impacton the growth of faster, smarter, and more efficient industrial networks.Higher-level protocols such as Profibus offer the high performance levelsrequired in automation applications. The lowest level of automationis the actuator and sensor level where the AS-Interface (AS-i) is used(Figure 8-1).AS-iThis standard was invented in 1990 as a cost-efficient alternative tothe conventional hard wiring of binary field devices. As-i has been usedin hundreds of thousands of installations. Originally, AS-i focused on theconnection of low-level binary devices with a single, easy-to-mount,two-conductor cable that carries power and data.AS-i is now an international standard under EN 50295. It is a vendor-independentbus network that is open to any manufacturer. AS Internationalis the sponsor organization of AS-i. It was formed in 1991 bya consortium of 11 manufacturers who developed the international standard.Today, the association has over 100 member companies that supplymore than 600 products and services. AS International is also responsiblefor the conformance testing and certification of devices.Connection to Higher LevelsAS-i provides a low-cost solution for connecting binary products,such as sensors, actuators, valves, and relays, with higher-level©2001 by The Fairmont Press, Inc. All rights reserved.