A Device Description is similar to a driver for the device. For fieldbus devices, the Device Description includes the calibration procedures, parameter procedures, and other information required by the control system to communicate with the fieldbus device. Standard Device Descriptions are provided by the FOUNDATION Fieldbus specification and optional, incremental Device Descriptions are provided by the device manufacturer. Device Descriptions are written in the Device Description Language (DDL) and the host system such as the DeltaV system uses library functions called Device Descriptions Services to read the Device Descriptions. Device Description technology enables interoperability among fieldbus devices. Interoperability, a key benefit of fieldbus technology, is the ability of a host system to operate multiple devices, independent of manufacturer, on the same fieldbus segment without loss of minimum functionality.
The DeltaV system supports a number of fieldbus devices from different manufacturers. The device description files necessary to support these devices are included in the DeltaV install image. If a fieldbus device is not included in the DeltaV install image, you must install the device description for that device. The device description is specific to the device type and revision. The device files are packaged in device install kits and can be found on the DeltaV website under Resources. The device description files must include a file with an .fhx extension to work with the DeltaV system. You can download the device description files to a disk, CD, or directory on your system and then use the DeltaV Explorer to add the device type to the DeltaV Explorer library. Install the device description files on the ProfessionalPLUS workstation and the DeltaV system synchronizes the device descriptions on the other workstations. Refer to DeltaV Explorer help for information on how to use the Add Device Type command.
Device Descriptions can also include a set of processing routines called Methods. Methods provide a way to access and manipulate parameters within a device. For example a DD for a Valve Controller might include methods for automatically calibrating valve travel, manually calibrating travel, restarting a device, and calibrating the internal pressure sensor information for display. Methods are available from the device's context menu in DeltaV Explorer.