Open field device management must support the plant life cycle with a homogeneous tool chain according to fig. 1. The essential functions are:

• open management of all components (field device asset management);
• open engineering (parameterisation);
• open commissioning (setting equivalent values); and
• open diagnosis and maintenance (conducting function tests).

In commissioning a plant, application-specific settings are made by changing parameters in the field devices. This parameterisation requires electronic tools which are often implemented as programs on Windows-based computers. In the past every field device was usually assigned to one corresponding parameterisation tool, which meant that every new version of the field device had a potential effect on the parameterisation tool. Merely adding a single parameter due to a function extension in the device forced users to revise the corresponding tool program.

To improve the situation, two electronic methods of field device parameterisation have been developed:

• the driver component-based (FDT) method; and
• the description data-based (EDD) method.

The first method was published as a regulation by the Profibus User Organisation under the term 'Field Device Tool (FDT)' and is characterised by implementing Active-X driver components in place of independent parameterisation programs.

The second method is also published as a regulation by the Profibus User Organisation. It makes use of the E-Business trend towards electronic description of product properties by simple data records ('Electronic Device Descriptions, EDD') and their interpretation by browser tools.

Let us take a closer look at these two methods.

In this method, the field device manufacturer provides a parameterisation tool in the form of an Active-X-based driver program, the 'Device Type Manager (DTM).' The appropriate driver program is installed for every field device type contained in the plan in a frame application (fig. 2). The number of driver programs to be installed increases with the number of field device types available in the plant. The concept is similar to that of the printer drivers in a Windows environment. A style guide should ensure, as much as possible, a uniform HMI of the driver programs. The control system supplier provides the FDT frame application in his engineering system. He is responsible for the integration of the different driver programs.

Revision of a field device is always connected with revision of the driver program and its re-installation or update in the control system. More than 10 years of experience with the approximately 750 HART field devices have shown that there has been one modification on average per field device per year. This example makes it obvious how great the maintenance effort for the driver programs will be.

In the opinion of Siemens, the FDT method is less suitable for parameterisation of field devices. It has interesting architecture features for implementing engineering tools, but lacks standardisation. It is offered for example by Pepperl+Fuchs in the form of the PACTware program package.

In the description data-based solution, the concept of descriptive product data records in the form of EDDs is used. The technique is comparable with an Internet browser which interprets Hypertext Markup Language (HTML) pages, displays them on the screen and enables inputs and process sequences with the difference that EDDs of the field devices are interpreted instead of HTML pages (fig. 3).

An EDD is created by the field device manufacturer with the internationally standardised language called 'Electronic Device Description Language (EDDL).' It contains, for example, the statistical product data necessary for parameterisation, and the relationships and manipulation instructions for these data. If the manufacturer revises his field device, he supplies the browser tool of the control system with a new EDD. It is not necessary to create a Windows program because the EDD is independent of the operating system.

EDDL is harmonised in the form of IEC standard 61804-2 and the description technique of the three user organisations HART, Fieldbus Foundation and Profibus User Organisation.

The standardised browser tool is provided by the control system manufacturer. Today for more than 1,000 different Profibus and HART field device types, such a browser tool is for example Simatic PDM, the Process Device Manager from Siemens.

Simatic PDM adapts quasi 'individually' to every field device by evaluating the EDDs. Since the appropriate device descriptions for all HART field devices were available from the beginning, the 14 million field devices installed over the last 12 years are accessible with Simatic PDM immediately.

The functions for handling all components in a plant—not just the field devices—is summarised under the term plant management. The Prolist project group initiated by Namur (NE 100) relies fully on descriptive techniques for electronic support of the plant planning, component ordering, commissioning and maintenance among other things (fig. 4). Tests have revealed that only description-oriented methods can be used for such purposes. Since open field device management is part of the future fully electronically supported plant management, its method is of prime importance.

In the future it will be crucial to provide data from thousands of different field device types (fig. 1) consistently and uniformly. Open field device management is part of data-oriented plant management according to Namur recommendation NE100. In Siemens' opinion, it can only be description-based.

Siemens advises its customers to use FDT/DTM technology only for parameterising complex devices where currently available technologies are not sufficient. DTMs will involve additional software costs, either direct or indirect, and the user will have to pay them. It is difficult to estimate what these additional costs will be.

The reason we are sure the user will pay additional costs is a consequence of the inevitable upgrades and new releases of DTMs, due to 'innovations.' These will cause effort and add-on costs for the whole lifetime of the field instrument.

For all other devices the established, standardised and proved EDDL technology should be used rather than changing hundreds if not thousands of devices by misled 'innovation.'

—Dipl. Ing. Hans-Georg Kumpfmüller, Head of Process Instrumentation and Analytics Division, Siemens Automation and Drives (A&D); Hansgeorg.Kumpfmueller@siemens.com