Civil Engineering Reference
In-Depth Information
faster and less disruptive installations and retrofits;
smoother and less costly migrations staged to accommodate budgets and
schedules.
Flexibility is the ultimate benefit in deploying a wireless system compared
to a wired network, while sensors can be located, or relocated, to optimize
system performance, increase customer comfort and adapt to changing floor
plans. Many wireless technologies and products are available in the current
BAS industry, and a great deal of effort is being expended to develop wireless
technologies for BAS applications. Wireless BAS will have great prospects in
BAS installations in the very near future, although many aspects still need
to be addressed.
There are many short-range wireless communications technologies avail-
able now in IT, automation and other mobile data-communication fields. The
wireless technologies related to BAS applications are mainly:
ZigBee technologies
;
802.11 compliant (Wi-Fi) technologies
;
Bluetooth technologies
;
other proprietary technologies.
4.6.1 ZigBee technologies
The ZigBee Alliance developed a network specification that is built upon
the IEEE 802.15.4 radio. The standard was approved in December 2004
and adds logical network, security and application software. The standard
was created to address the market need for a cost-effective, standards-based
wireless networking solution that supports low power consumption, low data
rates, security and reliability. Potential applications include home automa-
tion, BA and automated meter reading, as well as industrial monitoring and
control. The range of the ZigBee devices with direct communication is 100
to 300 feet (30-91 m) for typical buildings, which makes it well suited for
BA applications.
ZigBee uses multiple network topologies, or configurations - star, mesh
or cluster tree (which is a combination of the star and mesh topologies).
The most suitable topology varies by facility. Regardless of which topology
is used, full function devices (FFDs), such as field panels powered by 24 V
AC, can route traffic from other nodes. In contrast, reduced-function devices
(RFDs), such as battery-powered, room-temperature sensors, are limited to
transmitting and receiving only their own traffic. ZigBee operates at multiple
frequencies, 250 Kbps at 2.4 GHz, 40 Kbps at 915 MHz (for US markets)
and 20 Kbps at 868 MHz (for European markets). It therefore occupies the
same unlicensed band as Wi-Fi and Bluetooth.
Search WWH ::
Custom Search