Actuators with fieldbus interface - AUMA - #19

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Bus features Development or notified certifica­tion body Fieldbus Foundation www.fieldbus.org Concept/communication principle Foundation Fieldbus basically distinguishes between three different communication mechanisms: Publisher-Subscriber for cyclic process data transfer, Client-Server for diagnosis, parameter setting and configuration as well as report distribution for signalling alarms. There is no master, the data is directly exchanged between the field devices. The bus communication between the field devices is directly coordinated by the LAS (Link Active Scheduler). The LAS function is per-formed by one of the field devices for each segment. LAS capable field devices are called Link Masters, basic devices cannot perform the LAS function. Applications Chemical industry, petrochemical industry, power plants, pharmaceutical industry and food industry as well as paper industry and mining Versions FF-H1 based on IEC 61158 with a baud rate of 31.25 kbit/s. This is the FF technology directly connected to the field devices. FF-HSE, based on Ethernet (100 Mbit/s). The data is transferred via HSE both within the DCS as well as bet-ween the DCS and the linking devices. Generally speaking, a linking device can be considered as converter between the quick HSE and the slow H1 version. AUMA actuators support the FF-H1 version Physical layer For H1: IEC 61158, with 31.25 kbit/s, bidirectional data transmission, half-duplex. Power supply and data transmission is performed on the same wires. Foundation Fieldbus devices with low-current consumption can be supplied via bus. Maximum number of devices 240 field devices including linking device. A maximum of 32 devices can be connected to a single Foundati­on Fieldbus segment. Typical number of devices Usually 6 - 10 (max. of 12 - 14) per segment; mostly 4 H1 ports are available at a linking device, i.e. approx. 25 - 40 devices per linking device. Since FF is frequently used in large plants, often several linking devices are used. Typical bus cycle time 500 ms - 2 s, depending on the number of devices Data transmission rates of the bus 31.25 kbit/s Max. cable lengths without repeater 1,900 m Max. cable lengths with repeater The maximum cable length which can be implemented depends on the number of the repeaters. For FF, a maximum of 4 repeaters may be cascaded. Redundancy concepts For Foundation Fieldbus, the redundancy is only specified within the HSE (i.e. up to the linking devices). For the further H1 wiring to the field devices, there is no redundancy provided. By means of link master devices, some kind of implicit redundancy can be established for FF: if the LAS (link active scheduler) fails, another link master device can automatically take over the LAS function and can continue to co-ordinate the bus communication to the other devices. Device integration/ remote programming of the slaves Client-server messages are used to program and configure Foundation Fieldbus devices via Foundation Fieldbus. All information required for these requests are stipulated in the device description of a Foundation Fieldbus field device which is imperatively required. All in all, the device description consists of three files (*.ffo, *.sym and *.cff). The device description has to be installed in the DCS so that the device data (e.g. parameters, operating data, or electronic name plate) can be read or modified from the control room using Foundation Fieldbus. The device description files of the AUMATIC AUMA controls can be obtained from www.auma.com or www.fieldbus.org. Fieldbus termination For Foundation Fieldbus, the termination consists of a resistor with an in series connected capacitor which is connected to the FF+ and FF- wire at the beginning and the end of a main segment. The longest cable length within a Foundation Fieldbus network is called main segment. AUMA products provide these fieldbus termination resistors and do not require external termination resistors. | 19