Instrumentation Concerns and Recommendations

Summary: In this episode I discuss instrumentation concerns and recommendations, with my guest Djair Zanini. We cover common issues that Djair sees in his role as a Senior Mechanical Engineer responsible for mechanical solutions and instrumentation retrofits at Nexus Controls.

Topics Covered:

• Top 4 most common instrumentation concerns
• Potential impacts of instrumentation problems
• Root causes such as thermal changes, vibrations, line pulses, and more
• Recommendations to prevent or minimize issues

Guest Bio: Djair is a Senior Mechanical Engineer responsible for mechanical solutions and instrumentation retrofits at Nexus Controls. Djair has over 30 years of experience working with complex mechanical systems controls and instrumentation applied in hydro plants, thermal plants and other rotary equipment. His past roles include Project Engineer, Bently Nevada Engineering Manager, Lead Mechanical Engineer and Senior Mechanical Engineer.

In a Distributed Controls System (DCS), why is it important to understand instrumentation concerns and recommendations?

Instruments are a vital part of any DCS.  Instrument performance can impact the entire manufacturing process. Consequently, understanding instrumentation challenge areas and how to avoid and troubleshoot them is a priority for achieving safe, proper manufacturing performance.

Standard instrumentation concerns include stability, installation, noise, and variation. Safeguards for these concerns encompass both foundational and ongoing measures. Since unexpected issues with instrumentation may be connected to production escalations, substantial capital losses, or catastrophic events, it is imperative to stay on top of these potential developments.

The Nexus Controls platform provides a complete DCS solution to help customers prevent issues before they occur or deal with them in real-time: including controlling and monitoring the plant equipment and the related instrumentation. In turn, this ensures safe, cost-effective operations.

Common instrumentation concerns

Most instruments used in DCS-managed manufacturing processes present four types of challenges:

1. Stability. Continuity is a challenge due to instability, which happens over time as instruments get out of tune, requiring periodic recalibration.
2. Installation. A key challenge of the installation process is ensuring a good connection of the instrumentation to the system.  During installation, the connection may loosen and, in some cases, even disconnect completely. This can isolate the instrument, making it useless to the system.
3. Noise. Noise is everywhere and can disrupt instrumentation signals. Thus, operators are challenged to reduce sources of noise that can interfere with the instruments.
4. Variation. The variation in the instrumentation types, brands, and methods of operations can be a concern. The plant maintenance manager has an essential role in minimizing instrumentation variation.

Potential impacts of instrumentation problems

Instruments are essential to DCS operation and, as such, can impact the entire manufacturing process. Unexpected issues with instrumentation may be connected to production escalations, substantial capital losses, or catastrophic events.

As an additional safeguard, dual or triple redundant instruments may be required for critical or safety control loops; for example, over-speed protection and control/lubrication failure trips. Making the instruments dual or triple redundant, along with periodic recalibration, increases the costs of the instruments and the installation process, however, it also ensures smooth and secure operations.

Frequent instrument failures can cause another problematic situation. Instrument malfunction can cause “false trips”. These non-emergency failures can change the operator’s reaction to actual emergencies by desensitizing them to more severe problems that may be occurring with the instrumentation.

How to prevent instrumentation issues

There are some general recommendations and best practices that can help to prevent instrumentation issues. Proactively avoiding an issue before it escalates into a broader scale problem is always a best practice, often at the lowest possible cost.

As the first foundational step, instruments must be correctly specified and installed per OEM (Original Equipment Manufacturer) recommendations. The second foundational step is to have proper physical mounting, wiring, and voltage-level separations. Together with protective conduits, these practices help prevent signal noise, process disconnection, degradation, and plugging.

New technologies are also helpful in preventing instrumentation issues.  Some new technologies use HART instruments or FOUNDATION fieldbus (FF) devices. These devices have similar capabilities but use different protocols. While HART and FF instruments do not eliminate the need for recalibration, they may help monitor instrument conditions and prevent unexpected failure. That’s because the HART and FF devices generate more information from instruments across the network and can help diagnose – and thus prevent and/or minimize -- future failures.

Routine maintenance practices help prevent instrumentation issues. For example, conducting grounding checks as a maintenance priority. Also a recalibration program is a preventive measure to ensure instrumentation performance and should be part of routine maintenance.

In addition, consolidating the instrument information in a historical database for analysis is also ideal for all loops, especially critical ones. A control loop refers to the parameter that is being managed, such as a speed loop, pressure loop or temperature loop. One recommended practice is to use triple redundant instrumentation for critical loops. For steam and gas turbine applications, Nexus Controls recommends triple redundant loops for over-speed protection and in critical assets for lubrication and control oil low pressure trips.

In summary, these actions help to prevent instrumentation issues:

Foundational:

• Instrumentation. Instruments must be correctly specified and installed per OEM recommendations.
• Installation. Instruments must be properly installed with appropriate physical mounting, wiring, grounding, and voltage-level separation.
• Redundancy. Use triple modular redundancy on critical loops to prevent having major issues when a device is down.

On-going:

• HART and FF devices. Use HART and/or FF devices to proactively monitor, capture, and analyze additional information on instrumentation health.
• Ground-fault checks. Do regular ground-fault checks as part of on-going maintenance.
• Calibration program. Put a calibration program in place to ensure devices are recalibrated on a regular basis and operating within their ideal window.

Additional instrumentation health recommendations

Additional instrument challenges can emerge based on the specifics of a manufacturing environment. Take, for example, a steam turbine. Most steam turbines have older control systems that share the same oil for lubrication and the control system, thus contamination is a big concern on this type of equipment. As a digital control system is adopted, the mechanically and hydraulically driven governors are replaced with servo valves that are more sensitive to contamination. The best practice adopted by Baker Hughes is segregating the control fluid from the lubrication system.  At Nexus Controls, high-pressure HPUs (hydraulic power units) specifically designed for the control valves are used to completely segregate the control fluid from the lubricating system. This provides higher reliability of the control loops and the control systems, as well as longer life for the attached instruments.

In addition, Baker Hughes has developed and implemented fully triple redundant shut down manifold blocks. These permit continuously monitoring each of the independent oil circuits and automatically exercising the critical overspeed valves with the equipment online, under normal operation. This can provide operators valuable data about the equipment protection system allowing countermeasures without unexpected/undesired trips. Exercising components in hydraulic circuits is extremally important, both to monitoring their condition and to expelling minor traces of contamination that may accumulate in the small tolerance passages, which are known causes of blocking.

Nexus Controls solutions

Nexus Controls offers complete solutions to ensure optimal control and performance. Components include control panels, valves, instruments, cybersecurity, and services. The Nexus OnCore Control System can either be a simple control system for individual equipment or a complete DCS solution used to control and monitor a large portion of plant equipment. Nexus OnCore solutions may include the re-specification and replacement of instrumentation to meet digital systems requirements.

The Nexus OnCore Control System also employs an intuitive HMI (human machine interface) and historian database. The historian database can be used as a proactive tool, to analyze past events and better anticipate potential problems before they occur.

Nexus Controls customers have access to the expertise of Nexus Controls’ technical support team and remote diagnostics team to help prevent instrument performance issues before they occur as well as help deal with them when they cannot be prevented. The goal is to provide a complete end-to-end solution for critical control and protection loops, ensuring foundational safeguards, ongoing protection, and cost savings.

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