Excellent PLC
By Marcus Field – Plant Reliability Engineer
Day 23, Week 12 – Heavy Rain Forecast
Came in this morning, got the first report: “Fan 3 stopped.”
Walked down to the motor room. Fan spinning fine. Bearings quiet. RPM steady.
Checked the Bently 1900/55-01-02-01-01 fan monitor. Alarms flashing. Data showing fan down intermittently.
First thought: sensor failure.
Observation:
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Environment very humid, condensation on ducting.
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Monitor module sitting near the ceiling, close to a roof vent.
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Slight dripping on wiring junctions.
Strange thing: only Fan 3 misbehaving. Others in the same room fine.
Hypothesis:
Moisture ingress. Maybe a tiny short in the monitoring module caused false “stopped fan” signals.
Grabbed a multimeter.
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No complete short, but insulation resistance lower than spec.
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Every slight vibration made readings fluctuate.
That explained the intermittent alarms. Sensor itself fine. Fan itself fine. Module just misbehaving under humidity stress.
Actions Taken:
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Removed module cover. Checked for condensation. Cleaned contacts.
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Applied conformal coating on electronics for temporary moisture resistance.
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Rerouted cabling away from dripping points.
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Monitored readings through a full fan start/stop cycle — stable.
After a few hours, no false alarms. Humidity slowly decreasing, data remained clean.
Takeaways from Today:
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Even robust monitors like the 1900/55-01-02-01-01 can be sensitive to environmental moisture.
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Short circuits don’t always destroy the module — sometimes they just cause intermittent errors.
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Quick field fixes (clean, reroute, protect electronics) often prevent unnecessary downtime.
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Always verify actual fan operation before trusting alarms blindly.
End of Log:
Today was a reminder: sensors and monitors don’t just measure—they interact with the environment. Humidity, condensation, dust, vibration… all of it matters.
Sometimes, the machine isn’t broken. The module just thinks it is.
— Marcus