Yokogawa FLXA402 — pH Calibration

Correct calibration procedure for FLXA402 pH / ORP analyzers. Calibration aligns the transmitter to the sensor condition — it does not repair a damaged sensor.

Important: Frequent calibration indicates sensor aging or process issues.

Preparation

  • Ensure stable process or remove sensor from process.
  • Use fresh, unopened buffer solutions.
  • Confirm correct temperature compensation.
  • Rinse sensor with clean water (do not wipe glass).

2-Point Calibration (Recommended)

1) Immerse sensor in first buffer (pH 7).
2) Wait until reading stabilizes completely.
3) Accept first calibration point.
4) Rinse sensor and immerse in second buffer (pH 4 or 9).
5) Accept second point after stabilization.

Acceptance Criteria

  • Slope typically between 90–105%.
  • Zero offset within manufacturer limits.
  • Slow stabilization = fouled or aged sensor.

Post-Calibration Checks

  • Return sensor to process carefully.
  • Observe pH trend stability.
  • Confirm correct 4–20 mA scaling.
  • Document slope, offset, date, buffer batch.