Stay up to date with Motive Dynamics news. http://motivedynamics.com Wireless HART - How it worksWirelessHART is a wireless mesh network communications protocol for process automation applications. It adds wireless capabilities to the HART Protocol while maintaining compatibility with existing HART devices, commands, and tools.Each WirelessHART network includes three main elements: Wireless field devices connected to process or plant equipment. This device could be a device with WirelessHART built in or an existing installed HART-enabled device with a WirelessHART adapter attached to it. Gateways enable communication between these devices and host applications connected to a high-speed backbone or other existing plant communications network. A Network Manager is responsible for configuring the network, scheduling communications between devices, managing message routes, and monitoring network health. The Network Manager can be integrated into the gateway, host application, or process automation controller.The network uses IEEE 802.15.4 compatible radios operating in the 2.4GHz Industrial, Scientific, and Medical radio band.The radios employ direct-sequence spread spectrum technology and channel hopping for communication security and reliability, as well as TDMA synchronized, latency-controlled communications between devices onthe network. This technology has been proven in field trials and real plant installations across a broad range of process control industries.Each device in the mesh network can serve as a router for messages from other devices. In other words, a device doesn't have to communicate directly to a gateway, but just forward its message to the next closest device. This extends the range of the network and providesredundant communication routes to increase reliability. The Network Manager determines the redundant routes based on latency, efficiency and reliability. To ensure the redundant routes remain open and unobstructed, messages continuously alternate between the redundant paths. Consequently, like the Internet,if a message is unable to reach its destination by one path, it is automatically re-routed to follow a known-good, redundant path with no loss of data. The mesh design also makes adding or moving devices easy. As long as a device is within range of others in the network, it can communicate.For flexibility to meet different application requirements, the WirelessHARTstandard supports multiple messaging modes including one-way publishing of process and control values, spontaneous notification by exception, ad-hoc request/response, and auto-segmented block transfers of large data sets. These capabilities allow communications to be tailored to application requirements thereby reducing power usage and overhead.- This excerpt was taken from the Hart Communication Foundation website ::. http://motivedynamics.com/news/index.asp?w=news&q=detail&nid=11 Many times, rotating equipment are combined with components that do not share the same inspection or replacement frequencies. For example, tilt pad bearings constraining a high speed shaft may have a service interval of 50khrs at speed. In contrast, the ball bearing in an oil pump assembly may only be rated for an equivalent 5 years of service at speed. Ball Bearing Useable Life"Ball bearings were formerly rated on thebasis of the compressive stress in the most heavily loaded ball. Except forstatic loads, experience has shown that the actual cause of failure is fatigue.Fatigue characteristics are used for load rating and are dependent onexperimental results. Analytical methods are available to determine aparticular bearings useable life. Consult with manufacturer to determinetypical bearing performance characteristics.The life of a ball bearing is thelife in hours at some known speed, or the number of revolutions, that thebearing will attain before the first evidence of fatigue appears on any of themoving elements. Experience has shown that the life of an individual ballbearing cannot be precisely predicted. Fatigue characteristics are used for loadratings.Even if bearings are properlyinstalled, adequately lubricated, protected from foreign matter, and are notsubjected to extreme operating conditions, they can ultimately fatigue. Underideal conditions, the repeated stresses developed in the contact areas betweenthe balls and the raceways eventually can result in fatigue of the materialwhich results in spalling of the bearing load carrying surfaces. In mostapplications, the fatigue life is the maximum useful life of a bearing." Source: www.EngineersEdge.com http://motivedynamics.com/news/index.asp?w=news&q=detail&nid=10