Reference Manual
Rosemount 708
Appendix C Recommended Practices
Effective Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page
EFFECTIVE RANGE
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.
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