Using hardware intelligence in original systems

HART® technology lends itself in particular to the expansion of existing systems. As evidenced in its ever broader distribution HART® has become a definite industry standard.

Somewhat less ideal for auto-mation, since its data transfer is relatively sluggish, HART® technology nonetheless displays its strengths in the areas of troubleshooting, diagnosis, start-up and maintenance.

Despite the relatively low data transmission rate it can for suitable applications (such as tank storage systems) be used to create multidrop-networks, a mere step away to fieldbus technology.

In HART® technology (Highway Addressable Remote Transducer) an analog output (4-20 mA) is used for digital, bidirectional communication. The line length can be up to 3 km. HART® is a de facto standard and is supported by most manufacturers of auto-mation components. HART ®

The Hart Commands

With HART® all information is transmitted via commands. There are 3 groups:
Universal Commands
These ?Commands? must be supported in all HART® devices. This guarantees that the most important information on a device can be read and understood by any HART® operating device, such as:
Up to 4 measured values or meter values l Value of the current output in mA and percent l TAG I.D:, description of the measurement point and specific device number l Measurement range limits and units of measurement. The following values can be written: l TAG, description of the measurement point and specific device number l Brief messages
Common Practice Commands
These Commands cover the functions that many but not all field devices must have. All commands of this class supported by the field device must be executed exactly according to their definitions.
Device Specific Commands
All functions that are not covered by the two command classes described above are described in Device Specific Commands.
Device Description Language
The Device Description Language (DDL) describes device functions and their presentation in a formal language. The Device Description (DD) is obtained from the DDL via a compiler. This DD can be loaded into the bottom of the operating which is then able to record the functionality of the field device. This has made manufacturer-independent control possible.