Servomex 4900 — Alarm Decision Trees
Technician-grade alarm handling based on real refinery experience. Follow the sequence strictly to avoid false calibration and unnecessary sensor replacement.
Golden rule: Always stabilize sample flow, pressure, and moisture
before touching calibration or sensors.
Sample Flow Alarm
Flow below design limit or unstable (pressure hunting).
Typical root causes:
Wet / blocked filters — 45%
Regulator hunting — 30%
Process pressure loss — 15%
Internal restriction fault — 10%
Wet / blocked filters — 45%
Regulator hunting — 30%
Process pressure loss — 15%
Internal restriction fault — 10%
Oxygen Sensor Fault (Paramagnetic)
O₂ signal unstable or outside physical limits.
Typical root causes:
Moisture ingress — 40%
Pressure shock / hunting — 25%
Wrong zero gas / leaks — 20%
True sensor failure — 15%
Moisture ingress — 40%
Pressure shock / hunting — 25%
Wrong zero gas / leaks — 20%
True sensor failure — 15%
Communication Alarm
Analyzer values not updating in DCS.
Typical root causes:
DCS quality-bit issue — 45%
Network / switch fault — 30%
Power / UPS reset — 15%
Analyzer service stopped — 10%
DCS quality-bit issue — 45%
Network / switch fault — 30%
Power / UPS reset — 15%
Analyzer service stopped — 10%