Device diagnostics on the move

Field devices transferred a large amount of extremely diverse diagnostic information and literally flooded users with data. The Namur Recommendation NE 107 “Self-monitoring and diagnostics of field devices” corrects this situation by compressing diagnostics into four easily comprehensible status functions. Its clear and well-structured presentation has considerable benefits for plant operators and maintenance personnel. They now only receive the information they actually need and no longer thousands of superfluous measurement details. Uncertainties related to plant operation and fault elimination are thus avoided. The ideal technology, which gets the maximum possible leverage from the added value of the diagnostic functions in modern field devices is FDT; it permits seamless integration of devices, networks and applications spanning different manufacturers and protocols.

The FDT2 specification has been available to the public for almost a year now. The new standard is downwardly compatible and guarantees the continued openness of all fieldbus protocols, maintenance of the basic architecture and support for the existing DTM (device type manager) functions. FDT2 is based on Microsoft.NET technology. Among the advantages of this latest standard are the ready-made “common components”, which ensure that the standard components of DTMs or frame applications are consistently developed for FDT2. This accelerates the market launch of certified FDT products – and generates cost reductions for device manufacturers. DDs (device descriptions), EDDs (electronic device descriptions) and future FDI device packages (field device integration) are supported in addition to the DTMs. All these different processes can be combined with one another in any manner in a single FDT environment. The increased efficiency lets users build up device catalogues in the shortest possible time within the frame application. The new standard supports a divided architecture, e.g. several frame applications that access a common database.

“Standardised diagnostics in accordance with Namur Recommendation NE 107 permit a change from the previous maintenance strat-egy of rigid, cyclical and often unnecessary intervals to flexible maintenance as and when required. Device integration can thus save a great deal of money”, explains Juan Garcia, Product Manager at Vega. “Our sensors carry out continuous, internal monitoring and diagnostic tasks. The results of these activities, together with the four defined statuses – maintenance requirements, function check, failure and outside the specification – are made available to the process control system in the form of a compressed diagnostic message.” If maintenance is expedient, the responsible personnel can then request more detailed information from the sensor explicitly via the corresponding sensor DTM and, where neces-sary, introduce suitable measures.

If, for example, the signal-to-noise ratio of a Vega plics radar sensor becomes smaller and smaller, the reason for this could be product adhesion on the antenna. Cleaning the antenna can then be planned selectively. Modern technology such as radar provides many options for routines and checks to help users optimise the processes in their plants. The device status can be queried in a targeted way by means of the available DTMs using FDT frame applications such as Pactware – the free, non-proprietary operating software which is independent of fieldbuses – to configure and parameterise the field devices.

The use of a larger measured value memory allows data to be acquired and saved on site at the sensor. Furthermore, the plicsplus device generation is provided with an event and diagnostic memory for logging operations – all combined with a unique time code. Echo curves, for example, can be saved and analysed after reading out the memory.

To meet customer requirements for categorised diagnostic messages, Endress+Hauser also focuses on open standards. “Our DTMs for all Hart, Profibus and Foundation fieldbus devices have a standardised diagnostic module, which implements NE 107 consistently and independently of the communication protocol on the basis of the fieldbus specifications”, says Sandra Wesner, Head of Technology Marketing at Endress+Hauser Process Solutions. “Users thus receive exactly the information they require in order to react quickly and correctly.”

The measuring technology from E+H is state-of-the-art and extends the fieldbus specification for standardised diagnostic messages consistently in the devices, for instance with the Foundation fieldbus, the “FF-912”, and Profibus, the “Profile 3.02”.

The dynamic diagnostic information is displayed automatically in FDT-based plant asset management tools, such as Endress+Hauser’s FieldCare, after opening the device DTM. It consists of a coherent error message in text form, the possible cause of the fault and exact instructions for action. Faults can thus be corrected without having to resort to the operating instructions and with no detailed knowledge of the device while diagnostic information can be processed faster and more efficiently.

Yet what use is the finest device diagnosis on the bottom level in the field device if the information cannot reach the process control system at the top because there are problems with the network? Although two thirds of all users believe that continuous monitoring of fieldbus networks is vital, only a few have actually implemented it up to now. It could all be so easy – as demonstrated by Pepperl+Fuchs and Trebing+Himstedt.

Wherever continuous and reliable operation is paramount, the installation technology of a fieldbus system is increasingly the focal point of fitters and maintenance teams: the failure of the fieldbus topology can have serious consequences. The fieldbus segment must be characterised by high quality and equally high availability. What’s more, measures to ensure it remains that way are a must. “The fieldbus topology of the Foundation fieldbus H1 and Profibus PA becomes a controllable plant component with the help of diagnostic tools such as the Advanced Diagnostic Module (ADM). The fieldbus is now a lot easier to handle”, comments Thomas Westers, responsible for process automation training and committee work at Pepperl+Fuchs. “All information is available via the DTM in the safe environment of the control room. Entry to the plant is unnecessary, and that enhances personal and plant safety.”

Automated test tools are employed for installation inspection and monitoring. They perform a loop check using the optimised communication network as a basis. The Pepperl+Fuchs Advanced Diagnostic Module (ADM) offers high operating convenience, inspects the fieldbus topology, documents the connected field devices, logs deviations and compares them with the planning document. Using an expert system, the ADM indicates irregularities in the installation – precisely, simply and comprehensibly in plain text. Typical installation mistakes such as inadequate shielding, earthing errors, incorrect termination or short circuits are remedied quickly.

With its web-based TH Scope software and network access via TH Link, the Profibus-Ethernet gateway, Trebing+Himstedt offers a cross-network monitoring system for Profibus, Profinet, Ethernet/IP, Modbus TCP and Industrial Ethernet. Networks can thus be monitored on the fly in an uncomplicated manner and malfunctions detected early. The diagnostic software is capable of monitoring several fieldbus networks and communication protocols in one application simultaneously.

“Standardised, modern and user-friendly operating concepts for asset management systems are indispensable”, says Katja Große, responsible for Marketing Industrial Communication at Trebing+Himstedt. “The application not only provides central access to different field devices from the FDT frame application but also plant-wide, parallel monitoring of both the fieldbus and the field devices. All of this is available without any additional effort.” Users benefit from a standardised diagnostic system for heterogeneous fieldbus protocols as well as commissioning, operating, inventory and maintenance support. No special knowledge of the communication protocols of the monitored equipment is required to use the monitoring system. Thanks to the intuitive operating interfaces, automatic alarm signalling in the event of errors or problems and simple display based on the traffic light principle, network or device errors are indicated promptly, so that the plant is continuously available. Diagnostic messages in plain text and information on the cause allow errors to be eliminated quickly and efficiently.

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