FDT/DTM or EDD? Choosing the best open device-management

Paul Boughton

For example, process and plant data and status information are available to the control system at all times, and the process instrumentation devices can also be managed, parameterised, commissioned, and serviced via fieldbus.
The prerequisite for this approach is an open field device management system that supports the appropriate management, service, and engineering functions. We share the opinion of the Profibus User Organisation (PNO) whose guidelines advise that DTM technology should be used in complex distributed devices, leaving the description data-based variant which is a more robust and lower-cost solution for regular process instrumentation devices.

Open engineering is key

In the past, each individual device usually had its own engineering tool with which the device parameters could be adapted and modified – in other words, there were as many tools as there were field device types.
To simplify this increasingly complex situation, the first solutions offering open, manufacturer-neutral device management tools were introduced a few years ago. This meant that the user had to choose between two methods: the established description data-based method and the new driver component-based method.
The driver component-based solution was published by the PNO as a directive under the name FDT. The parameterisation tool is based on an ActiveX program supplied by the manufacturer as a driver for the respective device. This DTM is installed in a master frame application. The concept is similar to that of printer drivers in a Microsoft Windows environment. The control system supplier responsible for the integration of the various driver programs provides the frame application with an FDT interface in the engineering system.
The number of driver programs to be installed increases with the number of field device types in the system. Manufacturers can use the DTM style guide for orientation to ensure that the HMI of the various driver programs is as uniform as possible for the various process instruments.

At the moment, there is no standard apart from the PNO directive that defines the content and form of the DTM interface. With the DTM approach, the revision of a process instrument usually involves the revision of the driver program and its reinstallation or update in the control system.
On average, one change is made per device per year, so the driver programs must be modified and installed that often as well. In addition, cross influences or compatibility problems between different driver programs or with the control system software in which the Device Type manager Drivers are integrated cannot always be completely ruled out.
In the description data-based solution, the concept of descriptive (product) data sets – EDD – is used. This EDD is read and interpreted by a browser; this is similar to way an internet browser interprets and displays HTML pages. The device manufacturer creates the EDD in the internationally standard Electronic Device Description Language (EDDL), which contains the static product data necessary for parameterisation of, among other things, the device’s context and the manipulation instructions for these data. If the manufacturer modifies its field device, it supplies the control system’s browser tool with a new EDD. The EDD is independent of the operating system, so no Windows-specific programs need to be created.
The control system manufacturer provides the similarly standardised browser tool. For EDD interpretation, Siemens has developed the Simatic PDM process device manager, with which more than a thousand different Profibus and Hart field device types can be managed.
Since the appropriate device descriptions for all Hart field devices are available, the IEC-compliant Simatic PDM can provide immediate access to all the 14million Hart and Profibus devices installed over the past 12years.
Simatic PDM is a universal cross-manufacturer tool for configuration, parameter assignment commissioning, diagnostics and maintenance of intelligent process devices and automation components.
With Simatic PDM, you can use one software program to configure a number of field devices by different manufacturers using a single user interface. Process device data can be easily set, changed, checked for plausibility, managed and simulated. In addition, you can monitor selected process values, alarms and status signals of devices online.
The core functions are: setting and changing device parameters; comparison of setpoint and actual parameter assignment; plausibility check on entries; simulation; diagnostics; management; commissioning; function, eg measuring circuit testing of process device data.

Advantages in industrial applications

The considerable maintenance effort required under some circumstances for FDT/DTM technology must be taken into account in the assessment of both solutions (Table1).
Therefore, FDT/DTM technology is only recommended for parameterisation in complex devices in which other available and tested technologies are insufficient. For less complex process instrumentation, the description data-based concept is a more robust and reliable solution that has proven itself in a widely installed device base. Electronic Device description is the technically optimum and best-proven solution for instruments in the chemical industry.

Mark McCormick is Product Manager for Profibus at Siemens Process Instrumentation & Analytics, a division of Siemens Automation and Drives. For all technical enquiries tel 00 44 (0) 1905 450500 or visit "