Profibus expands

Werner Rüdiger, Dr. Ulrich Jecht

In the ZVEI, the German Electrical and Electronic Manufacturers Association, process analyser manufacturers first commenced their activities in field bus technology in 1990. They developed a document describing the functionalities of different types of analyser in a single, standardised form. Due to changes on the field bus market the group was only able to decide in favour of Profibus as the preferred field bus for process analysers in 1995. In 1997 10 manufacturers finally formed a group whose aim was to jointly develop hardware and software for connecting process analysers to Profibus-PA. The development work was performed by the Institute for Automation and Communication (ifak) in Magdeburg. It included the development of an „Analyser“ profile for Profibus-PA together with documentation such as a device data sheet, the bus interface design (hardware) and the implementation of the profile and the communication functionality (software).

The profile was developed according to the block model, which describes the device functionality in blocks. Different block types are used for certain groups of functions and parameters. The physical block describes the analyser through its measuring principle, device configuration, serial number, etc. The function blocks describe the execution of certain functions such as data evaluation, alarm handling, logbook control, etc. The transducer blocks describe the actual measuring procedure. This includes control functions such as measurement, calibration, measuring accuracy determination, special limit value control, etc.

An interface board based on the H8/3003 microcontroller was developed for connecting the analyser to the bus. It was given a flexible design with the different analyser

types and development concepts of the group members in mind. This interface board can be used as a tool for further developments or as the device interface itself.

The joint development has been successfully concluded. The results enable manufacturers to achieve a device-specific implementation into their own analysers. The majority will consider both the RS 485 and the IEC 1158-2 serial port, because process analysers are often installed also in non-explosive areas. Analysers with RS 485 will be called DP-devices and those with IEC 1158-2 PA-devices, both using the same protocol and profile however. Several manufacturers have almost finished the implementation and will present the first Profibus-DP/PA analysers at the Interkama fair in Duesseldorf.

So-called ‘engineering tools’ are available from different suppliers for engineering, installation and handling as well as for diagnosis and servicing of field devices. The relevant device profiles must be implemented into the tools using a description language, which is still tool-specific today. Standardisation is also planned for this task, however. Engineering tools for process analysers will be available by the end of 1999. The analyser profile will be implemented into process control systems in a similar way, to allow direct communication between the PCs and the analysers.

Profibus

Fax: ++49/721/9 65 85 89

Further information cpp-202