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The Evolution of Control Valve Diagnostics condition reporting
- Jul 13, 2018 -

In the 1990s there were many ideas regarding what a digital positioner could or should do and what was needed from it. But power was limited to 4 mAmps, so the systems had to be designed to analyze what was most important for the application: diagnostics or performance? It is not possible to have both when power is limited.

However, micro-processors developed very rapidly, going from 8 bit to 16 bit to 32 bit in a very short time, so much more could be done. Manufacturers could focus on better performance algorithms and add diagnostic and pneumatic pressure sensors. Valve position sensors started off with potentiometers, but they had a propensity to break, so manufacturers moved to magnetic non-contact sensors. As the valve moves, the orientation of the magnetic field moves, so these sensors could tell how and where it was moving. LED lights or LCD with buttons and menus also came into use, and these also offered increased access and reliability.

However, diagnostic features remained relatively unchanged and the challenges of control valve diagnostics remained. Positioner self monitoring and alarms made it possible to perform tests and have continuous diagnostics, which was helpful, but often yielded an incomplete picture of the root cause. It was non-deterministic.

Offline diagnostic signatures were also valuable, but are only possible when the process was down, and the schedule was often based on maintenance of other equipment. Thus, the value for predictive maintenance just wasn’t there. It was possible to tell if the valve spent a lot of time closed to the seat, but that may or may not be valuable information for a particular application.

Finally, online diagnostic monitoring became possible. It requires only a minimum valve movement to be relevant and relies heavily on control system integration via HART I/O or FF. The advantages include continuous diagnostics; it is the first line of defense in a tiered diagnostic strategy. It is also good for trending the valve operating environment.

Online diagnostics provide a much better, continuous analysis. The positioner can tell you what’s going on, so you can perform online diagnostics for real-time trending. You can monitor as often as you want and when. It can be initiated on a scheduled basis or be condition-based monitoring, in real time. Valve problems can be isolated from control loop performance or a predictive maintenance management program can be implemented.

Cloud-based storage of valve data makes it possible to have all the information on the bill of materials (BOM), and maintenance and repair history so it’s possible to determine if the valve really is healthy. It is possible to have more and more easily accessible data, including the complete valve life cycle.

It’s becoming so advanced now that a technician can wear a smart helmet that allows him to talk with somebody at the factory or another subject-matter expert. That expert can consult with him on that control valve, because that distant person can see what the technician sees through video cameras also on the helmet. This is going through testing now to make sure it is effective.

With all this remote monitoring, cyber security becomes an issue, so safeguards must be built in. One safeguard makes it impossible to move or change the valve from a remote monitoring location.