Quarantine physical layer defects: Isolate and root out dodgy network installations that yield intermittent errors

摘要

A valve positioner had been consistently showing up in diagnostics, and the site's ability to view its troubles over time helped convince maintenance to plan a replacement. So last fall they pulled and rebuilt the entire valve and replaced the positioner with a new one, including the latest Hall effect position feedback array. Everything checked out well on the bench and after the valve was reinstalled. But come spring, the communication "drops" began showing up in the event logs again. It was curiously intermittent - there would be no errors for days, and then another shift log would complain of fleeting alarms that typically cleared immediately.