PLANTS use a mix of field devices from different suppliers and multiple brands exist on package units. Main Instrument Vendor (MIV) concepts reduce the mix but new types are introduced by mainte nance replacement, and they must inte grate with the system.
Since the original DD technology had no graphics, two kinds of systems existed: those without device graphics, and those using proprietary graphics solutions. Systems without graphics could not support sophisticated devices like radar level transmitters so a laptop with special software had to be used.
The systems using proprietary graphics supported advanced devices from the same manufacturer, but were not fully interoperable with third-party devices. These early conditions made Foundation fieldbus more difficult than it should have been.
Other protocols also needed standard graphics, so in 2004 the Fieldbus Foundation, HART Communication Foundation, Profibus Nutzerorganisation e.V. (PNO), and OPC Foundation formed the EDDL Cooperation Team (ECT) to enhance traditional DD technology with graphics and a flexible menu system.
Graphical elements
As a result, device manufacturers were empowered to format the display of their devices in the control system using standard IEC 61804-3 EDDL graphics.
The graphical elements include images, graphs, charts, gauges, bar- graphs, histograms, bar-charts, and tables. These tools enable device manu facturers to make devices that are intu itive to set up and diagnose.
Further tools carried over from original DDs including parameter labels, wizards, conditionals, and context sensitive help.
Interoperability is improved because all device features are accessed as intended by the device maker.
Multi-vendor EDDL (Electronic Device Description Language) interoperability was demonstrated at the ISA Expo 2008 and independ ently confirmed by the BIS Prozesstechnik (formerly Infraserv Hoechst) in Germany.
EDDL is the key to interoperability, whereby devices from multiple vendors integrate with their full features. Look for the EDDL logo to select devices that interoperate with your system.
Traditional DD displayed device diagnostics spread across multiple "pages" (displayed in different places in the menu) corresponding to resource, sensor transducer, diagnostics, and function blocks.
Because diagnostics were split up among the different blocks many clicks were required to troubleshoot the device, or for setup.
New EDDL "Device Level Access" merges parameters from multiple blocks displayed together onto the same page formatted by the device manufacturer. Therefore, configuration and trou bleshooting is simplified.
Device setup made easy
Devices in a plant range from simple pressure and temperature transmitters to sophisticated (complex) valve posi tioners, analysers, machinery health transmitters, radar level transmitters, variable speed drives, and bus diagnos tics modules. All should be managed from the same software.
Some devices cannot be set up using simple parameter values; they require graphics to convey information. For that reason, they could not be set up with traditional DDs.
Although host systems support DD files, many did not yet fully implement the technology.
For instance, display of a human readable label such as "Damping" instead of a cryptic parameter name "PV_FTIME" was missing. DD features like "Wizards" and "conditionals" were missing, as was access to the help text.
Foundation fieldbus was more diffi cult to use than it should have been. A new hierarchical menu system displays parameters and status indica tors arranged as a structured tree and logically grouped on pages, tabbed cards, and within frames for intuitive navigation.
New setup solution
Enhanced EDDL enables setup of advanced device features. Images illus trate relationship between parameters like tank dimensions, or options such as different valve flow characteristics.
Graphs display multiple signal wave forms, for instance radar level trans mitter echo curve and filter thresholds simultaneously. It’s the system software that allows the user to pan and zoom any graph provided by any device. Therefore any graph in any device is analysed the same way.
Only EDDL provides such consis tency. Tank strapping table and valve flow characterisation are edited in an Excel-like format. EDDL parameter labels identify configuration settings and diagnostics.
Previously, pH sensor standardisa tion and radar level transmitter echo curve threshold setup required the technician to navigate to the right blocks, set the right mode, and write the correct values to a series of parame ters- all in just the right order. It was not user friendly. With systems supporting EDDL wizards, these procedures are much easier.
The wizards are created by the device manufacturer’s experts, guiding the technicians step-by-step through complex procedures. For instance, for pressure transmitter zero trim, the tech nician is first reminded to inform opera tions to put the loop in manual, then to apply zero input (isolate, equalise, and vent the manifold).
Next the device trims its zero, after which the technician is reminded to inform operations that the control loop can be returned to automatic. The complex sequence of manipulating specific parameters is automated, and all technicians follow the same standard procedure.
EDDL wizards drive handheld field communicators used for in-situ valve stroking and sensor trim, for example to correct for mounting position. Device manufacturer expert know-how guides tasks with explanatory text.
Previously, device pages had endless lists of parameters with endless lists of options, most of which were irrelevant to the typical application.
It was not as easy as it could have been. However, full implementation of EDDL in the systems has solved this problem.
Internal dependencies
EDDL "conditionals" is logic in the EDDL file to handle complex internal dependencies between parameters, only displaying the required settings and rele vant options based on prior selections. For instance, in a radar level transmitter the dimensions of custom sized probes are only prompted if a custom probe is first selected.
EDDL supports help text for param eters and diagnostics. In the past, device manufacturers did not bother providing it. However, ease-of-use and extent of help information is becoming a compet itive differentiator. Leading device manufacturers share their expert know- how and experience in help text.
Graphics should not overwhelm the technician. New more powerful devices internally automate setup. For instance, a radar level transmitter analyses the echo curve and automatically adapts the threshold, eliminating manual curve fitting. That is, EDDL enhancements simplify Foundation fieldbus setup. Technicians must be able to solve many different problems that may affect the mix of devices in a plant. Incomplete support of DD labels, wizards, and conditionals in early fieldbus systems restricted effectiveness.
EDDL enhancements make diag nostics easy and attractive. Device manufacturers include images to make interpretation of diagnostics easier. EDDL "conditionals" show different images depending on status. For instance, display a product photo pinpointing the fault.
Device manufacturers know their device best and share know-how as explaining text, assisting in the deciding on the appropriate action.
Some diagnostics are easiest inter preted as graphics, for example machinery health transmitter vibration spectrum or valve signature.
Another example is a fieldbus signal shape from a bus diagnostics module. Multiple waveforms are displayed simultaneously for comparison and correlation. Pan and zoom is the same for all waveform graphs and trend charts. Trend charts make it possible to follow the trend of secondary measure ments, like ambient temperature that is not logged by the system histo rian, to spot causes of intermittent prob lems. Multiple pens are displayed in the same trend chart for comparison and correlation.
Dial gauges visually show how close a value is to the limits. Side-by-side bar graphs make comparison against setpoint easy.
Bar-charts show hourly, daily, and monthly maximums for a value such as valve "stiction". This makes spotting long-term shifts in operation easy.
Histograms are used to detect wrong sizing by showing at what position the valve spends most of its time.
The content of the device’s internal event log can be reviewed for clues during troubleshooting.
Leading device manufacturers compete, providing the most complete "actionable" help text for the diagnostics uncovered by the device. Graphics should not overwhelm the technician. New more powerful devices interpret diagnostics to simple actionable instruc tions instead of showing pages and pages of graphics and reports. Ironically, future devices will not need as many graphics since EDDL enhancements make troubleshooting easier.
Without compromise
The NAMUR NE 105 recommenda tion for device integration requires a system to remain operational for 15 years in spite of new Windows versions, and to be kept current with new devices without jeopardising system robustness.
While traditional DD’s could not support full device functionality for some devices, they met all other user requirements and have an enormous installed base.
Graphically enhanced EDDL provide full access to device capability without compromising the original DD advan tages, thus meeting all user require ments. EDDL files are not made obsolete by new Windows versions, service packs, or .NET framework because they are compressed text, not software. Similarly, the files are not conflicting with each other or system software components.
The EDDL file for a new device is copied, not installed, and no license keys are required.
Look and feel is consistent because common elements like graph and trend toolbox, parameter editing and colour coding are rendered by the system regardless of type, manufacturer, or protocol.
There is no need to grapple with a second technology since all the NAMUR requirements are met with EDDL. Windows-independent EDDL files protect the investment, and preserve system robustness.
By escaping tricky software driver installation, the system is easy to keep up to date with new devices.
The consistent look and feel makes devices more intuitive, and their features easier to benefit from. Absence of file license keys further simplifies system administration.
Alternative software driver based device integration sacrifices robustness, suffers faster obsolescence, requires more IT skills and license key administration, and has less consistent look and feel.
Integrated smart diagnostics
A drawback of 4-20 mA is that 20 mA may mean high PV (e.g. high level) or device failure: the operator cannot discern. In event of this reading, a technician had to be sent to check the device.
Device diagnostics in Foundation fieldbus devices distinguish a device problem from a process problem. However, device diagnostics are mean ingless unless they are incorporated into maintenance practices.
It is not practical to display diagnos tics on a separate maintenance station because technicians are in the field; they don’t see the device alerts as they appear on the station, and don’t take immediate action.
Further, operators will not move over to the maintenance console to search for suspected problems. As a result, non-integrated device diagnostics fall into disuse.
It typically takes minutes or hours before a device problem escalates into a process problem. Through device diag nostics in operator consoles, operations get fast indication of device failure as an early warning of impending problems.
Operators cannot fix the device, but have time to respond before process is affected. They first tend to the process, and then request maintenance to inspect the device.
Operators should not be flooded with all diagnostics. Only failures affecting the process are displayed on operator consoles. The devices and alerts are prioritised according to criticality in the process when the system is engi neered. Some devices are more critical than others.
Failed transmitter
Some device faults are more serious than others. For instance, the operator needs to know about a failed transmitter, but not about something that will only fail months later.
This ability to categorise device fail ures and assign priority is the intent of Foundation fieldbus’ new "Field Diagnostics" based on NAMUR NE 107 and PlantWeb Alerts.
The classification and priority is transmitted as part of the device alert to the system when the fault occurs, and is used by the system to filter the notification to the operator or techni cian. EDDL is instrumental in the digital plant architecture that uses the power of field intelligence to improve plant performance.
Only DD and EDDL enable inte grated diagnostics, because the files are compressed text, not software drivers. Foundation fieldbus is versatile but does not integrate all devices found in a plant. EDDL, can integrate other protocols to fill the gap.
Enhancements
EDDL is also used to integrate HART for safety devices, Profibus DP for motor control, and WirelessHART for incre mental monitoring, complementing use of Foundation fieldbus for control.
Foundation fieldbus made diagnos tics configuration easier because users could diagnose without going into the field. EDDL enhancements now make setup and interpretation of diagnostics more intuitive.
Enhanced EDDL provides all the benefits of graphics without the draw backs of software drivers.
Upgrade to enhanced EDDL makes device management easier without making system administration more difficult by adding a second technology.
[Jonas Berge is Director PlantWeb Consulting, Emerson Process Management.]