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Yokogawa OX400 — In-situ Oxygen Analyzer

In-situ oxygen analyzer for combustion optimization (boilers/heaters). Technician focus: probe/filter condition, purge (if equipped), calibration line integrity, and stable installation.

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Technician rule: For unstable O₂, check probe/filter condition and calibration line leaks first. Don’t calibrate until the signal is stable.

Working Principle

OX400 is an in-situ oxygen analyzer typically based on zirconia sensing. It measures oxygen at the probe tip and converts it into a stable O₂ output for combustion control.

  • Measured value: oxygen concentration (O₂) in flue gas.
  • Key requirement: stable probe temperature and a clean sensing surface.
  • Accuracy depends on: probe condition, installation position, calibration integrity, and stable furnace conditions.

Main Components (Field Focus)

  • Probe/sensor assembly: sensing element, protective filter, mounting flange.
  • Electronics/transmitter: display, diagnostics, outputs, comms.
  • Calibration system: cal gas port(s), tubing, valves/solenoids (if equipped).
  • Purge/cleaning (if equipped): purge air path, purge valve, filters.
  • Wiring & outputs: 4–20 mA, relays, Modbus/Ethernet depending on configuration.

Calibration Procedure (Technician Sequence)

1) Confirm analyzer stabilized (warm-up complete / stable trend).
2) Check probe/filter: clean if heavily fouled; ensure no plugging.
3) Leak check calibration lines (most common reason for bad calibration).
4) Apply calibration gas (low/zero O₂ as per plant practice). Wait for stabilization.
5) Apply span gas. Wait for stabilization. Confirm reading matches standard.
6) Return to process. Verify stable output and correct DCS scaling.

Tip: If signal is unstable, extend stabilization time and confirm there are no leaks.

Major Troubleshooting (Top Issues + Fast Checks)

  • O₂ reading unstable: probe fouling, leaks, purge issues, unstable process conditions.
  • Slow response: plugged filter, heavy dust, installation location issues.
  • Wrong O₂ vs portable analyzer: compare after stable period; check calibration gas and leaks.
  • Calibration fails: incorrect gas, insufficient flow, leaks, not enough stabilization time.
  • DCS mismatch: scaling/range incorrect, comms mapping, output wiring.
Unstable Reading Tree → Probe Fouling Tree → Calibration Failure Tree → Communication Fault Tree →

Discussion

Share OX400 troubleshooting tips (fouling, calibration leaks, unstable O₂). (Requires GitHub login.)