wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

12-6 Industrial Communication Systems
humidity in equatorial regions. In addition, many plants and facilities are defined as hazardous locations,
where strict requirements apply to any equipment installed in potentially explosive areas.
National regulations for equipment operating in hazardous areas vary from country to country.
In the European Union, the 94/9/EC ATEX (ATmosphère EXplosible) [94/9/EC] directive is the governing
document, and for the United States and Canada, the North American Hazardous Locations
Installation Codes (National Electric Code for the United States and the Canadian Electrical Code for
Canada) define rules and regulations on equipment and area classifications’ requirements for hazardous
locations. Most other countries in the world adhere to the hazardous locations certification documents
from the International Electrotechnical Commission (IEC).
Before deployment of a WSN in a plant or facility, it is imperative to verify that the equipment is constructed
to withstand local weather conditions, and in the case of deployment in a hazardous location,
that the equipment has the required certifications according to national rules and regulations.
12.5 technology Survey and Evaluation
In Section 12.4, a set of requirements for the operation of wireless instrumentation in industrial application
was identified. One of the requirements states that the wireless technology should be based on
international standards. A growing number of standards for WSNs are emerging. This chapter contains
a survey and evaluation of the standards which are suitable for industrial wireless instrumentation.
12.5.1 IEEE Std 802.15.4
The IEEE Std 802.15.4 defines the PHY and the MAC sublayer for low-rate wireless personal area networks
[802.15.4]. The standard specifies four different PHYs, shown in Table 12.1. The two optional
high-data-rate PHYs in the 868/915.MHz band were introduced in the 2006 revision of the standard.
The IEEE Std 802.15.4 defines a total of 27 channels, numbered 0–26. Channel 0 is in the 868.MHz
band with a center frequency of 868.3.MHz. Channels 1–10 are in the 915.MHz band, with a channel
spacing of 2.MHz, and channel 1 having a center frequency of 906.MHz. Channels 11–26 are in the
2.4.GHz band; the channel spacing is 5.MHz; and the center frequency of channel 11 is 2.405.GHz.
12.5.2 ZigBee
The ZigBee specification [ZigBee], initially released in 2004 and updated in 2006, is a low-rate, lowpower
WSN standard developed by the ZigBee Alliance. The specification defines network and application
layers on top of the PHY and MAC layers of the IEEE Std 802.15.4, and it is primarily targeting
home automation and consumer electronics applications. Since the ZigBee specification uses the PHY
and MAC layers of the IEEE Std 802.15.4, they have the same modulation techniques, bandwidth, and
channel configurations. A ZigBee network operates on the same, user-defined channel throughout its
TABLE 12.1 IEEE Std 802.15.4 Frequency
Bands and Data Rates
PHY (MHz)
Frequency
Band (MHz)
868/915 868–868.6
902–928
868/915 (optional) 868–868.6
902–928
868/915 (optional) 868–868.6
902–928
Bit Rate
(kb/s)
20
40
250
250
100
250
2450 2400–2483.5 250
© 2011 by Taylor and Francis Group, LLC