As an automation technician, what's your most frustrating 'war story' about chasing intermittent faults that only appear on night shifts or during specific humidity conditions - and what diagnostic techniques finally cracked the case?

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Oh man, let me tell you about the most maddening intermittent fault I ever chased! It was a PLC-controlled packaging line that would mysteriously stop working only during night shifts, and only when the humidity was high. For weeks, we&#39;d get 2am calls about the line going down, but by the time we arrived, everything would be running fine again.The real breakthrough came when we started thinking like detectives. First, we installed data loggers to track temperature and humidity 24/7. Then we added remote monitoring so we could see the PLC status from home when those late-night calls came in. The key was realizing that the fault wasn&#39;t random - it correlated perfectly with condensation forming on certain I/O modules when the temperature dropped at night and humidity was high.The diagnostic technique that finally cracked it? We used thermal imaging cameras during a simulated night shift to spot temperature differentials, and then did a &#39;condensation test&#39; by artificially cooling specific components while monitoring for faults. Turned out to be moisture-sensitive optocouplers in the input modules that would fail when condensation formed. The fix was simple - adding desiccant packs and improving ventilation around the control cabinet. Sometimes the most frustrating faults have the simplest solutions, but you&#39;ve got to think outside the box to find them!

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As an automation technician, what's your most frustrating 'war story' about chasing intermittent faults that only appear on night shifts or during specific humidity conditions - and what diagnostic techniques finally cracked the case?

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