History in the Making
infoteam Software supports configuration of a device with the DTM in an FDT framework as well as presentation of device parameters and current measurement results including alarm and trend messages in ongoing operation. This technology is already being used in the Tirajana gas and steam turbine power generation plant in the Canary Islands.
Engineering and operation – two sides of the same coin
Engineering and initial startup are the phases in a system life cycle when non-existent, inadequate or just plain incorrect specifications cause the greatest problems for a general contractor’s engineering department. Given this scenario, the FDT/DTM standard is a significant step forward, which is reflected in a more secure planning basis and a shorter startup phase.
The FDT/DTM approach has been focused so far on the planning and maintenance phase, zeroing in on management of all devices attached to the fieldbus. This “asset management” approach has, however, excluded the operational phase so far. Namur has made recommendations for a color scheme and symbolism relating to the display of status information, measurement results and the way in which parameters are presented, but these recommendations have only been following in individual cases.
infoteam Software has combined the two approaches for SWAN Analytical Instruments on the “Central Termica de Ciclo Combinado de Tirajana” project, a gas and steam turbine power generation plant in the Canary Islands. The goal is to provide standardized displays to enhance the decision making process in plant operations. Devices are handled in the same manner using a DTM during initial startup and in the visualization process during ongoing operation. Both conform to the DTM style guide and recommendations. The solution was implemented using ActiveX technology. This article looks at the technical implementation and the resulting reduction of development effort and improvement in quality.
Graphic design of device specific DTMs
The increasing complexity of modern devices has ultimately led to a replacement of purely table based device description data using Device Description Languages by user definable DTM software components. This new functionality is essential to handle acquisition of quality data in addition to the actual measurement results. Typical for this class of devices are the PH-Redox meters made by the Swiss manufacturer Swan. These devices are used primarily in the treatment of feed water in power generation plants that use powerheat coupling. The PF level of the water must be kept within tight tolerances to protect boilers and lines. To exclude misleading measurements caused by invalid conditions such as excessive water temperature or blocked lines, additional equipment has been attached to these meters, for example a pump to control and monitor the flow of water through the meter. This ensures that the water which is analyzed actually comes from the power generation circulation system and that the measurement is not performed repeatedly on the same sample yielding false results due to a line blockage and resulting in costly damage to the pipeline system.
During the engineering phase for the pH monitor, complex relationships had to be specified in addition to simple parameters, and a plausibility check had to be made allready during device configuration. In the example of the pH monitor, this included flow, temperature limits, pH level and above all the maximum latency period after which a dosage of ammonia must have produced an increase in the pH level. It is not possible to check the dependencies between the parameters using current table-driven DTMs, so device-specific implementations become necessary. The pH monitor DTM could not be generated automatically as was the case in the past using the simple design planning tools that were available. Instead, a graphic editor was used to design the DTM, similar to the editors used to create the HMI. This is an integral part of the infoteam OpenPCS Automation Suite, and it supports the creation of system diagrams as well as the use of controls, menus, alarm lists and trend displays.
ActiveX toolkit for generating DTM templates
Because the user displays created with the visualization editor during the design phase will also be used by the runtime environment as a DTM, they have to be converted into an ActiveX component. This Microsoft technology is based on COM/DCOM and provides an excellent mechanism of encapsulating complex software modules. The ActiveX toolkit used in this application converts the graphic design of the DTM into an ActiveX component which is packaged together with the appropriate DTM library to provide the interfaces required by the FDT frame. The pH Monitor DTM is then supplied in the Profibus DTM library and can be linked into any FDT container for the project planning phase. The project planning user interface is then available to personnel during the planning and installation phase without the need for elaborate, device-specific programming.
Visualization in Open-PCS
Setting parameters for the pH monitors is a one-off activity which is performed during the system design phase. However, system operators must continually monitor correct operation of the measurement equipment, making standardized operation and display of device data a crucial factor. The operating philosophy used during the design phase must be maintained during ongoing operation. The scenario used for the FDT/DTM specification does not envision use of the FDT frame for visualization because established software products that do this already exist. The essential goal of the AQAS project is to standardize design and operation of a field device and to achieve a drastic reduction in the effort required to develop software components. Visualization of the pH monitors is derived from the design which was created for the DTM. The fact that the components used for trend display and alarm generation in OpenPCS are also available in ActiveX technology is also exploited.
Visualization of the meter is provided at the HMI in three variations:
- minimized overviews, for example the system diagram using a de-vice symbol such as a valve or other devices
- detailed views as an instrument with dual-color scales to display the pH value and temperature of the probe
- maximized using the DTM style to display current measurement results, pre-set parameters, trends and any alarm messages.
The reduced display in the first two views provides a vehicle for compact display of the Pipe and Instrumentation Diagram (P&ID) in AQAS, and shows the operator a quick overview of the key measurement results. Activating the symbols, for example by touching them on a touch screen, brings up the maximized view. This view shows measurement results and parameter settings, and alarms lists and trend diagrams can also present data in graphic form. The example in the illustration above shows a comparison between correct measurement results and deviant curves for a defective sensor. AQAS technology provides the basis for future analysis which complies with the requirements of current safety standards, human tissue processing or food production (IEC 61508, IVD guideline, FDA 21 CFR 11). WLAN, Bluetooth and Internet integration In addition to replacement of detergents during on-site calibration and sensor replacement during maintenance activity, operators have to continually make entries at the meter itself. On the other hand, the meters are normally mounted in a fixed position in the system and only have a few simple control and display elements.
The graphical displays are usually centralized in the control room and cannot be viewed on the devices themselves. It would be preferable to have the ease of use features that are common in the control room available directly at the device. WLAN technology (wireless Ethernet similar to the systems used in the home environment) and the use of PDAs and Pocket Windows 2003 can be used to achieve this. The ActiveX components which were created for the DTM and visualization can be converted to PDA format and used as a portable control panel which offers all of the ease of use features. As the use of Bluetooth standard to link local devices becomes more widespread, the time may come when there is no longer a need for control and display devices. The maintenance engineer will then carry his “electronic screwdriver” (PDA) around with him.
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