Product category:
Fieldbus systems, Fibre-optic systems
News Release from: Siemens Automation and Drives | Subject: EDDL and FDT/DTM concepts
Edited by the Processingtalk Editorial
Team on 26 July 2005
Comparisons of EDDL and FDT/DTM concepts
Mark McCormick, Product Manager for Profibus at Siemens Process Instrumentation and Analytics compares and reviews the open device-management concepts of FDT/DTM and EDDL
There are two basic solutions for manufacturer-independent integration of field devices in asset management and control systems: driver-based concepts such as the relatively new field device tool/device type manager (FDT/DTM) technology; and well established description data-based solutions such as Electronic Device Description (EDD) The networking of intelligent field devices from different manufacturers via an open communication interface offers users significant advantages
This article was originally published on Processingtalk on 10 Apr 2006 at 8.00am (UK)
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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.
Siemens shares the opinion of the Profibus User Organization (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.
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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.
Open engineering interfaces are a decisive factor in the life cycle of a device.
Driver component-based concept.
The driver component-based solution was published by the PNO as a directive under the name Field Device Tool (FDT).
The parameterisation tool is based on an ActiveX programme supplied by the manufacturer as a driver for the respective device.
This Device Type Manager (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 programmes 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 programmes 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 programme and its reinstallation or update in the control system.
On average, one change is made per device per year, so the driver programmes 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 DTM drivers are integrated cannot always be completely ruled out.
Description data-based concept.
In the description data-based solution, the concept of descriptive (product) data sets 'Electronic Device Description (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 parameterization 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 14 million HART and Profibus devices installed over the last 12 years.
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.
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.
EDD is the technically optimum and best-proven solution for instruments in the process industry.
Summary of the basic features of EDD.
Based on description files.
Established, tried and tested technology that has been on the market for many years, and standardised; further development by the IEC in progress.
Uniform user interface for all devices.
Tool-dependent use; robust tool (PDM) available.
Independent of the operating system.
Summary of the basic features of FDT/DTM.
Based on software programs (driver concept).
First applications running; further development will be pursued by the FDT Joint Interest Group.
Individual user interface; flexible and versatile for display and handling of data, including graphics.
Tool-independent use; drivers run in frame application.
Version compatibility must be considered; the base is MS COM/Net .
The author of this review, Mark McCormick, is Product Manager for Profibus at Siemens Process Instrumentation and Analytics (a division of Siemens Automation and Drives).
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