Practical Industrial Data Networks:Design, Installation and ...

Foundation Fieldbus overview 207open system that supports interoperability and a device description language (DDL),which will enable multiple vendors and devices to be described as ‘blocks’ or ‘symbols’.The user would select generic devices then refine this selection by selecting a DDL objectto specify a specific vendor’s product. Entering a control loop ‘block’ with theappropriate parameters would nearly complete the initial configuration for the loop.Advanced control functions and mathematics ‘blocks’ are also available for moreadvanced control applications.14.6 Error detection and diagnosticsFF has been developed as a purely digital communications bus for the process industryand incorporates error detection and diagnostic information. It uses multiple vendors’components and has extensive diagnostics across the stack from the physical link upthrough the network and system management layers by design.The signaling method used by the physical layer timing and synchronization ismonitored constantly as part of the communications. Repeated messages and the reasonfor the repetition can be logged and displayed for interpretation.In the upper layer, network and system management is an integral feature of thediagnostic routines. This allows the system manager to analyze the network ‘on-line’ andmaintain traffic loading information. As devices are added and removed, optimization ofthe link active scheduler (LAS) routine allows communications optimization dynamicallywithout requiring a complete network shutdown. This ensures optimal timing and devicereporting, giving more time to higher priority devices and removing, or minimizing,redundant or low priority messaging.With the device description (DD) library for each device stored in the host controller (arequirement for true interoperability between vendors), all the diagnostic capability ofeach vendors’ products can be accurately reported and logged and/or alarmed to providecontinuous monitoring of each device.14.7 High-speed Ethernet (HSE)High-speed Ethernet (HSE) is the Fieldbus Foundation’s backbone network running at100 Mbits/second. HSE field devices are connected to the backbone via HSE linkingdevices. A HSE linking device is a device used to interconnect H1 Fieldbus segments toHSE to create a larger network. A HSE switch is an Ethernet device used to interconnectmultiple HSE devices such as HSE linking devices and HSE field devices to form an evenlarger HSE network. HSE hosts are used to configure and monitor the linking devices andH1 devices. Each H1 segment has its own link active scheduler (LAS) located in a linkingdevice. This feature enables the H1 segments to continue operating even if the hosts aredisconnected from the HSE backbone. Multiple H1 (31.25 kbps) Fieldbus segments canbe connected to the HSE backbone via linking devices.