Mn081

Common issues

• Unshielded individual-wire runs picking up electrical noise, causing erratic or spiking readings
• Sensor tip degradation/drift over time leading to a persistent offset from actual temperature
• Wire insulation damage from heat or chafing near engine/exhaust runs, causing open or short-circuit alarms
• Terminal corrosion in junction boxes causing intermittent alarm or no-reading faults
• Sensor-to-system channel configuration mismatch after a card or module replacement

Inspection checklist

• Verify the sensor reading against a calibrated reference thermometer where accessible
• Inspect wire runs for chafing, heat damage and secure clipping away from hot surfaces
• Check junction box terminals for corrosion and tightness
• Confirm alarm/trip setpoints match the machinery manufacturer's requirements
• Test alarm and shutdown function during planned maintenance, simulated or live where permitted
• Review the alarm system trend/history log for sensors showing drift or repeated spurious alarms

Service intervals

Critical spares

• Temperature sensor, individual-wire type, correct IP rating
• Junction box terminal blocks
• Heat-resistant signal wire, correct gauge
• Sensor mounting/thermowell hardware
• Cable gland/connector kit

Safety

• A drifted or failed temperature sensor can mask a genuine overheat condition on a bearing or exhaust run - treat repeated spurious alarms as a finding, not a nuisance to silence
• Work on sensor wiring near running machinery requires isolation and hot-surface precautions
• Do not disable an alarm point without recording it and informing the responsible engineer

Class survey

Alarm and monitoring system sensors covering essential machinery (main engine, generators, bearings, exhaust) fall under class requirements for the alarm and monitoring system; periodic function testing of alarms and shutdowns is typically required, with sensor calibration/replacement and any disabled or overridden alarm points recorded and reportable to class.