Yokogawa FLXA402 — Alarm Decision Trees
Model-specific alarm troubleshooting for FLXA402 pH / ORP analyzers. Follow the sequence strictly to avoid unnecessary recalibration or transmitter replacement.
Rule: Resolve sensor and process issues first.
FLXA402 electronics rarely cause pH instability.
Unstable / Fluctuating pH
- Check for air bubbles or intermittent immersion.
- Inspect sensor glass and reference junction.
- Verify proper grounding of piping and transmitter.
- Check sensor cable for moisture ingress.
Drifting pH Reading
- Reference poisoning (sulfides, proteins, heavy metals).
- Blocked junction or low electrolyte flow.
- Aging glass electrode (low slope).
- Temperature compensation mismatch.
Calibration / Slope Error
- Expired or contaminated buffer solutions.
- Insufficient stabilization time.
- Dry or cracked glass bulb.
- Slope outside limits → sensor replacement.
Temperature Alarm
- Broken Pt100 / Pt1000 element.
- Incorrect temperature sensor type configured.
- Poor thermal contact with process.
- Shared cable damage affecting temperature signal.
No Signal / Sensor Fault
- Broken glass bulb or disconnected sensor.
- Wet or damaged high-impedance cable.
- Incorrect wiring or terminal assignment.
- Confirm by connecting a known-good sensor.