How can a fieldbus system be implemented in an existing HART system?
HART and FF have one great feature in common – they both use Device Descriptions (DDs). This makes it possible to mix HART and FF in one system and get equivalent capabilities for device configuration, diagnostics and instrument management. Hardware for a mixed system needs some care. Either, a host must offer both types of I/O system, or the host can use only FF, with a HART-to-FF gateway to connect to the existing HART devices. But be careful of the speed difference! In some applications, HART communication is not fast enough to use for the control variables, especially if multidrop HART is used. A gateway may, therefore, have to include analogue I/O, with conversion to digital form for the fieldbus connection. In addition, it is not yet clear (at least, to me!) how a HART device should be “disguised” as an FF device by translating its data structures, preferably based on its HART DD. As far as I know, no HART-to-FF gateway yet exists.
