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More efficient maintenance of field devices

Remote I/O system with proactive diagnostic features
More efficient maintenance of field devices

The Namur NE 107 recommendation advises plant operators to use standardised, easily understandable status indications, allowing them to receive information quickly about the status of their field devices. Despite gradual implementation on various automation network levels, such signals have not been widely available in the last few years. Until recently, the recommendation had still not been implemented for remote I/Os. The IS1+ system fills this gap.

The author: André Fritsch Produktmanager Fieldbus&Remote IO, R. Stahl

Diagnostic data from field devices mainly serves the purpose of avoiding production downtimes – one of the largest loss factors in modern process plants – as far as possible. The Namur user association for automation technology in process industries published its NE 107 recommendation back in 2007 with the aim of channelling the diverse self-monitoring data and other process information provided by state-of-the-art technology more efficiently. This recommendation not only emphasises that all such information must be reliable and available at all times; it also stipulates that in the context of specific applications, diagnoses must be reported in the format that makes appropriate reactions easiest for operators. It is based on the principle that indications should be limited to the significant factors for each application. In other words, they must be freely configurable, depending on the task and level, since information requirements differ for users in the field, process control and asset management. On the other hand, a certain standardisation needs to provide clarity across all scenarios.
The recommendation suggests colour and symbol conventions for status signals to enable operators to grasp five classified statuses quickly and easily. A green LED stands for a valid process signal in regular operation. Blue signifies a valid signal where maintenance is required. Yellow represents a signal that is out of specification. Signals that are temporarily invalid during functional checks are marked orange. Red indicates an invalid signal due to a malfunction.
Reconciling conventions with NE 107
In the meantime, NE 107 has been implemented in some process control systems and the majority of asset management systems. Many modern fieldbus devices for Profibus PA or Foundation Fieldbus H1 also already follow the Namur recommendation or will do so shortly. Its implementation is planned (Hart) or specified (Profinet, FF HSE/F-ROM) for several other fieldbus systems. However, no remote I/O solutions conforming to this recommendation have been available in the last few years. When it comes to field devices and remote I/Os, it is important that NE 107-compliantly designed indications remain compatible with worldwide standards that are already established. Yellow and orange LEDs especially (plus white ones) have been used in the past to indicate the switching status of devices, as suggested by the NE 044 recommendation. Yellow, signal-specific LEDs for showing the switching status should therefore be restricted to systems implementing NE 107. R. Stahl’s new IS1+ remote I/O system follows this maxim. It features separate LEDs for each channel: as well as a yellow LED for digital I/O signals, there is also a red LED for inputs and outputs that flashes according to NE 044 if an error occurs on the line. On top of this, IS1+ modules have a three-LED block for device-related indications comprised of a green status LED, a red error LED and a blue maintenance LED. The latter lights up continuously to draw attention to an essential replacement owing to damage or wear. It flashes if a device is operated out of specification. Maintenance personnel can thus react in good time and take measures to prevent fail-ures. In addition to activating the blue LED, the module sends a diagnostic telegram to indicate that maintenance is called for. This information can then be analysed on a higher level, such as a process control or asset management system, and integrated via DTM in compliance with NE 107.
Use for proactive maintenance
The IS1+ system features not only LED indications based on NE 107 but also integrated wear detection. During operation, the remote I/O continuously measures all relevant module parameters like ambient temperature, system load and on/off cycles. Depending on these conditions, the actual realistic lifespan is calculated by reducing the maximum for nominal operation (15 years for this system), if applicable. The NE 107-compliant IS1+ monitoring function notifies users in good time – twelve months in advance – when a module approaches the end of its life. In most cases, this module can then be exchanged without any undue stress at the next convenient opportunity, so that operating and maintenance staff time is no longer wasted on unscheduled service assignments. Moreover, the detailed diagnosis prevents modules from being replaced unnecessarily according to a fixed cycle if they are likely to remain functional for some time to come. A system such as IS1+ allows users to benefit from the Namur recommendations in almost any automation environment, i.e. far more extensively than before. Unfortunately, NE 107 will still not be universally supported in future, and in particular not by all standard fieldbus systems. Above all, no implementation is planned for the widespread Profibus DP. However, the IS1+ system also provides a partial solution for this fieldbus, to enable process values to be transferred cyclically in the same way as with Profibus PA or Foundation Fieldbus H1. Like fieldbus technology, it uses a separate status bit for each channel to indicate whether the signal is within the specification or faulty. This IS1+ feature for Profibus DP anticipates the status information envisaged in a similar form for Profinet – though with a width of one byte instead of one bit.
cpp-net.com/0113420
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