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The Evolution of Control Valve Diagnostics
- Jul 11, 2018 -

Before the 1980s, all valve diagnostic methods were manual. Technicians used mechanical measuring tools, calipers, pressure gauges and the like. Documentation was manual and generally the methods relied tremendously on technician experience. There was no capability to remotely diagnose the health of a control valve.

Beginning in the 1980s, personal computers (PCs) came onto the scene, so they began to be used to do data acquisition by hooking up to the valve. That was the first venture into automatically gathering data from a control valve. Through this, it was possible to see what a valve was doing, its health and how well it was operating. This was adopted first in the nuclear power industry because of the high demand for accuracy.

Mostly it was control valve manufacturers providing this service. Their technicians would go into a plant during a turnaround, which was the only time the valves could be exercised. Time was of the essence, and everything was scheduled considering how much time it took to take the diagnostics, how much to set it all up and put it all back. While this was an improvement over the manual measurements, there still was no remote monitoring, and the use of the PCs and interpreting data from them was also very technician-experience dependent.

As microprocessors began to evolve beyond the PC, digital valve positioners were introduced in 1994. Hughes noted this technology got off to a rocky start because everything was proprietary, so it was difficult for communication to occur between systems to get diagnostics. Problems led to the need for a standardized protocol.

That led to HART (highly addressable remote transducer). According to Hughes, the idea behind this was that existing 420 mAmp command signals could be used and a digital signature could be superimposed over top of that. It was based on Bell Lab’s 202 standard (which came from caller ID). Limitations in HART led to the development of Foundation Fieldbus. It took a decade to agree on what the all-digital protocols would be, and they evolved throughout the 1990s.

From 2000 on, Foundation Fieldbus became the standard for new plants, and HART I/O was used for plants integrating valve information with the digital control systems. Plant asset management (PAM) software integration became more widespread and is now pretty much standard.

Online diagnostics software was introduced to validate performance and health while it was in service. This made diagnostics much more independent of technician experience in addition to being more consistent. The software can be programmed to determine what the best technician could ___from the indicators and give possible corrective action including even what spare parts might be needed.