During operation, a GC needs periodic calibration or validation. In the past this required special software and experience. To assist technicians in calibrating or validating the measurement, the GC manufacturers now use Electronic Device Description Language (EDDL). EDDL allows the GC to be operated from the same familiar device management software as the plant's other analysers and transmitters. EDDL also alerts GC technicians and plant operators to potential problems and provides solution guidance.

Plug-‘n’-Play Communication A GC and associated systems have many process variables and status signals, rendering hardwiring with associated junction boxes, cable trays, marshalling cabinets, I/O cards and cabinet space impractical.

Modbus/RTU over RS-485 and Modbus/TCP over Ethernet was used for GC integration for years. However, both required register mapping and custom display creations which were tedious and error prone, especially if scaled integers were used, which required ranges to be set. Special care had to be taken with documentation, configuration, verification at FAT, and change management - particularly when the GCs and DCS were not from the same vendor. Register changes late in the project often required major rework and caused delays. Proprietary protocols requiring special drivers were even more difficult. Due to the cost of engineering the Modbus communication, integrators tended to only bring across a bare minimum of overall GC status rather than detailed diagnostics. As a result, GC capability was not fully utilised, and plant personnel were left without the opportunity to better manage the GC and control the process because key information was not conveyed. Once in operation, any checks beyond the most rudimentary would require specialised or proprietary Amadas software only a GC expert is qualified to use.

Many plants have discovered the limitation of hardwiring as devices become more advanced. Similarly, most projects are putting in too much effort for the Modbus mapping, not just for GC but also for many other types of devices.

A digital architecture based the on the Foundation Fieldbus standard (IEC 61784-1 profile 1/1 of IEC 61158 type 1) is common in the major plants being constructed in recent years, including the largest refineries, petrochemical complexes, and LNG processing plants. New GCs use Foundation Fieldbus to connect to the DCS without any need for register mapping and associated documentation, simplifying verification at FAT, and making changes easy to manage. Input or output signals can be added late in the project without new I/O cards, running new wires, or shuffling registers. Older plants without Foundation Fieldbus can use linking device available from several suppliers as a gateway to the existing DCS

With Foundation Fieldbus, one single interoperable protocol is used across all instruments and analysers throughout the plant. Other devices can even share the same bus as the GC. For example, discrete process pressure, differential pressure, temperature, and flow transmitters on the sampling system with the GC connect to the same two wires and their readings can be used to validate the sample. The GCs become an integral part of the digital plant architecture that uses the power of field intelligence to improve plant performance.

Thanks to standard function blocks (IEC 61804-2) and alert mechanisms that are part of Foundation Fieldbus, analyser operations share the same process display, historian, audit trail, and alarm & event log etc. as the main DCS.

Foundation Fieldbus provides a new level of GC integration, beyond Modbus and far beyond hardwired, resulting in fewer engineering hours.

Common Software

The GC may need calibration or validation every few months, or every day in gas metering billing applications. This is a procedure which includes putting the GC output on "hold", switching the process stream to a reference gas stream, purging and running a few reference cycles, and lastly switching back to the process stream. Validation checks for deviation from the reference, while calibration also corrects the GC reading to match the reference.

Moreover, technicians must manage a mix of analysers and other devices around the plant from many manufacturers. In the past, even a simple GC check was done using specialised software only the GC expert was qualified to use. Modbus could convey simple status to the DCS, but without explanation or recommended action from the manufacturer. Technicians in many plants were suffering from too many specialised software applications for GCs, drives, radar level transmitters, flowmeters, etc. On top of that there was the issue of gaining IT department approval of each software application and keeping it up to date.

The EDDL standard (IEC 61804-3) provides a solution to these problems. EDDL (www.eddl.org) integrates the GC with the same universal device management software used for the other analysers and field instrumentation in the plant. This enables technicians to check the GC with the same device management software as the plant’s other field instrumentation. Technicians interface with all these devices in the same basic manner, which makes the mix of devices easier to use and manage. Technicians can apply what they already learned on transmitters to the GC and to any new devices coming to the plant later – thus reducing the need for additional training, and eliminating errors resulting from using multiple software systems. The device management software maintains a single audit trail for changes to all devices, as well as a single alarm log for all device events.

Using EDDL, the GC manufacturer's expert defines how they want the GC to be displayed in the system in order to make it easy to use. The device management software renders each device display with the 'content & structure' defined by the manufacturer, but with a common 'look & feel' for all devices regardless of manufacturer, type, or protocol. The mix of devices around the plant is displayed consistently and is therefore easy to use. Thus EDDL interoperability makes it easier for technicians to manage the wide assortment of devices in the plant and complete their work faster.

Task-based Human Interface Displays

The device overview page displays overall status and operational information such as which stream is currently being analysed, how long it has been running, and the cycle time. An additional view also identifies manufacturer, GC model number, version, and includes a product photo to help in locating the GC in the analyser shelter.

The analysis result page displays the Mole fraction of each component such as C6+, propane, i-butane, n-butane, neo-pentane, i-pentane, n-pentane, and nitrogen along with measurement status

Guided Validation & Calibration

EDDL wizards make GC calibration and validation quick and easy. The wizards guide the technician step-by-step, prompting only for the required information.. The wizard shows only valid options based on prior selections, and verifies entered values. The technicians are not misled or confused by irrelevant settings, and cannot miss required entries. The software is the same as used for validation of flowmeters or standardising pH analysers, etc.

For instance, thanks to Foundation Fieldbus and EDDL, it is easy to run the calibration sequence remotely before a load/unload operation is started. Similarly, if operators do not trust the results they are seeing on a sample stream analysis, they can run a validation to check against a known standard. If the results are erroneous, a calibration can be run, correcting the error in analysis. No need to wait for a service technician to respond to a call. This can save hours of lost product or up time.

Easy Interpretation of Diagnostics

Foundation Fieldbus alerts tell you when there is a problem. Using EDDL, the GC manufacturer explains what is causing the problem and how to fix it. Help text and illustrations are brought into the system through the EDDL file to guide technicians in interpretation of diagnostics for faster troubleshooting.

Using EDDL, the GC manufacturer's expert provides easy to follow recommended actions specific for each alert. There is no need to interpret complex chromatograms. The technicians can pack the appropriate tools, spares, and consumables to quickly solve the problem in the field the first time without returning to their inventory shop to pick up forgotten materials. This could save hours in down time.

Both operations and maintenance personnel are concerned with GC health. If the GC is not running or the reading is invalid, operators must take alternate steps to maintain production, while maintenance technicians must act quickly to get the GC back online.

Unlike other device integration technologies based on driver software components, EDDL is based on compressed text files and therefore does not conflict with system software. Thus, a unique characteristic of EDDL is that the diagnostics page can also be made available to operators at the DCS operator console, in less than three clicks - without special software, and without moving from computer to computer. This gives better visibility to the health of the analyser.

The operator can bring up diagnostics pages created by the GC manufacturer who knows the GC best. These pages show information the way the GC expert structured it, making the GC easy to operate and maintain. For instance, "no sample flow" means the sampling system or sample probe may have failed, the GC results are invalid, and the plant may be producing off-spec product. The maintenance technician has to fix the problem, but, depending on the operational philosophy of the plant, operator attention is also required to take care of the process. Only critical alerts for faults affecting the process go to the operator, so they are not flooded with non-critical alerts for minor issues not upsetting the operation.

When integrated in the operator console, intelligent device management software will become a natural part of daily work practices. Diagnostics becomes an early warning, reaching the operator before the process is affected. The diagnostics makes it easy to distinguish a process problem from a GC problem. If the process variable status is 'Good' this means the GC is healthy, any unusual analysis result is indeed a process problem. There is no need to call the technician to check the GC. The operator can straight away focus on solving the process problem. Conversely, if status is 'Failed' this means the result is invalid and technicians have to fix the GC, there may not be a problem with the process.

Interpreting chromatograms to troubleshoot or optimize operation is only for the GC specialist. For such software the GC also supports Ethernet.

Another advantage of EDDL is that the files are not made obsolete by new versions of Windows, and conversely that EDDL files do not force a Windows upgrade. This keeps the system administration burden at a minimum, saving time.

Improve Plant Performance

Plant performance can be improved by adopting plug-‘n’-play EDDL technology in combination with Foundation Fieldbus to gain advantages such as faster communication, easier documentation and testing, shorter commissioning, greater flexibility to accommodate late changes, and diagnostics from the control room. EDDL wizards, graphics, hierarchical menu structure, and help, save technicians time and avoid errors.