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Reference Manual
00809-0100-4708, Rev AD
September 2012
C-1
Rosemount 708
Appendix C Recommended Practices
Effective Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page C-1
All recommended practices should be followed to ensure highest data
reliability. Deviation from those best practices may require device repeaters in
the network to maintain 99% data reliability. The following are guidelines to
achieve the best possible Smart Wireless Network.
1. Each wireless network field should be scoped to a single process
unit.
2. Minimize the number of hops to the Gateway in order to reduce
latency. Contain a minimum of five wireless instruments within
effective range of the Smart Wireless Gateway.
3. Have at minimum three devices with potential communication paths.
For stronger performance, increase the required number of wireless
neighbor devices to four or five. This increases the number of
potential paths and thus optimized network performance.
4. Have 25 percent of wireless instruments in the network within range
of Smart Wireless Gateway. Other enhancing modifications include
creating a higher percentage of devices within effective range of the
gateway to 35 percent or more. This clusters more devices around
the gateway and ensures fewer hops and more bandwidth available
to WirelessHART devices with fast scan rates.
5. Keep path distance from Gateway to a minimum. For better
performance, the path typically is within range of one to two hops.
This will utilize path redundancy and create very short transit times.
6. Effective range is determined by type of process unit and the density
of the infrastructure that surrounds the network.
EFFECTIVE RANGE Heavy Obstruction: 100 ft. (30 m). Typical heavy density plant environment.
Cannot drive a truck or equipment through.
Medium Obstruction: 250 ft. (76 m). Typical light process areas, lots of
space between equipment and infrastructure.
Light Obstruction: 500 ft. (152 m). Typical of tank farms. Despite tanks being
big obstructions themselves, lots of space between and above makes for
good RF propagation.
Line of Sight: 750 ft. (230 m). No obstructions between WirelessHART
devices and devices mounted a minimum of 6 ft. (2 m) above ground or
obstructions.
For examples and complete explanations, refer to the IEC62591
WirelessHART System Engineering Guide:
http://www2.emersonprocess.com/siteadmincenter/PM%20Central%20Web
%20Documents/EMR_WirelessHART_SysEngGuide.pdf