FF Technology Basics
FOUNDATION fieldbus H1
Foundation fieldbus H1 is gaining increasing importance in process technology. This is due, for example, to the vast possibilities its bus system offers for device parameterization and diagnostics. It thereby eliminates not only the need for a special parameterization interface at the sensor, but also the arduous - and possibly time-consuming - way to the sensor, depending on where the sensor is installed.
At a transfer rate of 31.25 kbits/s, H1 uses the same IEC 61158-2-compliant physical bus characteristics as PROFIBUS PA. Using this technology, intrinsically safe, bus-powered devices can be connected to form a network. In doing so, the voltage supplied to the devices is superimposed by an information signal from the transmitting device, which is generated by modulating the supplied current.
In practice, H1 provides two different device classes. Basic field devices offer the typical field device functionality. They comprise a function block application, act as a publisher and subscriber of process variables, can transmit alarms and trends, and offer server functionality for host access and management functions. Link master devices can act as Link Active Schedulers and Time Masters. They are used for bus interfaces in process control systems or in Linking Devices. Capable of simultaneously operating many connections to multiple devices, they support both client and server applications.
FOUNDATION fieldbus HSE
Since H1 only has a low transfer rate for technical reasons, communication on the supervisory control level calls for a fast solution. Considerations to supplement H1 by a faster H2 variant have been dropped in favor of Ethernet technology. With regard to the required infrastructure, this decision offers a wide choice of products. Four device classes have been specified for HSE. Host Devices are PCs or control systems with Ethernet ports, which do not contain any function blocks or management objects themselves but communicate with HSE devices via Ethernet instead. Linking Devices are gateways between H1 and HSE.
A Linking Device is connected to an Ethernet and operates multiple H1 segments. It acts both as a bridge between these segments and as a gateway between the H1 devices and the devices operated on the Ethernet. In addition, it may also comprise its own function block application. Foreign I/O Gateways are components for integrating third-party fieldbuses, such as PROFIBUS DP. This is done by incorporating the objects of the foreign fieldbus into the FF architecture as multiple I/O function blocks. The fourth class consists of the Ethernet Devices. They are integrated directly on the Ethernet.