analysis/knowledge/operational_context.yaml

# CSH2 Cryogenic Pump — Operational Context Knowledge
# Practical knowledge that operators have but specifications don't document.
# Derived from maintenance_log.xlsx, Technical PDF, and data analysis.

sensor_trustworthiness:
  TT110:
    notes: >
      TT110 reads pipe wall temperature, not fluid temperature. After cooldown,
      it needs 10-15 minutes to equilibrate with the flowing cryogen. During
      transients (pump start/stop, flow changes), TT110 lags the actual fluid
      temperature by 5-30 seconds depending on flow rate.
    workaround: >
      For precise inlet temperature, use virtual T_inlet back-calculated from
      discharge state via ThermoProps (physics/thermo.py). The virtual sensor
      uses PT110 + TT130 + isentropic relations to infer inlet conditions.
    known_faults:
      - "Jul 16, 2025: 0-32K readings are sensor fault, not real cryo temps"
      - "Filter out readings during known warm periods where TT110 < 50K"

  FT140:
    notes: >
      FT140 is a Coriolis mass flow meter calibrated for LN2. When running LH2,
      the density difference (LN2: 808 kg/m³ vs LH2: 70.8 kg/m³) causes the
      raw reading to be 100-200x too high. The FT140Calibrator applies a density
      correction factor of approximately 11.4x.
    workaround: >
      Always apply FT140Calibrator (physics/ft140_calibration.py) density correction
      before interpreting flow readings. Near-zero flow at low pump speeds is
      expected and not a fault — the meter has a low-flow cutoff.
    known_faults:
      - "Raw FT140 reads ~100-200x too high for LH2 — apply correction"
      - "Near-zero flow at idle is expected, not a sensor fault"

  PT100:
    notes: >
      PT100 is stuck at -14.86 bar in the current dataset. This is not a
      physical pressure — it's a sensor fault.
    workaround: >
      Use default_when_invalid=2.0 barg for any calculations requiring PT100
      (e.g., Psat estimation). This is the saturation pressure approximation.
    known_faults:
      - "Stuck at -14.86 bar — use 2.0 barg default"

  CalcMass:
    notes: >
      CalcMass is stuck at 0.18 kg in the current dataset. The PLC calculation
      is not updating.
    workaround: >
      Use FT140 integration (corrected) for actual dispensed mass calculation.
      Integrate corrected FT140 over the fill duration.
    known_faults:
      - "Stuck at 0.18 kg — use FT140 integration instead"

  M130_Speed_vs_MC130:
    notes: >
      Tag 68 (M130_Speed) replaces tag 13 (MC130_VFD_Speed) after May 28, 2025.
      Both map to motor speed percentage but are different register addresses.
      TAG_ALIASES in config.py handles this mapping.
    workaround: >
      Check TAG_ALIASES. Use tag 68 for post-May data, tag 13 for pre-May.
      Both are valid speed readings.

post_maintenance_expectations:
  hp_seal_replacement:
    description: "After HP seal replacement or energizer work"
    expected_behavior:
      - "Initial friction: 7-9 kgf (from Jul 18 maintenance entry)"
      - "Break-in period: ~1000 cycles to reach 4-5 kgf steady state"
      - "Motor current will be higher initially — this is normal"
      - "Volumetric efficiency may be slightly higher initially (tighter seal)"
    timeline: "1000 cycles (~2-3 days at normal testing rate)"
    ref: "2025-07-18 maintenance event"

  icv_replacement:
    description: "After ICV replacement or reseating"
    expected_behavior:
      - "Immediate improvement in pressure build if ICV was the issue"
      - "New valve may need seating-in (initial performance varies)"
      - "Jul 22: orientation fix restored 700 bar immediately"
      - "Jul 14: polished ICV helped but didn't fully fix — surface not flat"
    timeline: "Immediate improvement expected"
    ref: "2025-07-01, 2025-07-14, 2025-07-22 events"

  dcv_polishing:
    description: "After DCV sealing surface polishing"
    expected_behavior:
      - "Immediate improvement in leak test results"
      - "Run PT130 decay test before and after to quantify improvement"
      - "Jul 1: polishing improved seal but some residual leakage"
    timeline: "Immediate improvement"
    ref: "2025-07-01 maintenance event"

regime_caveats:
  ln2_vs_lh2:
    description: "LN2 and LH2 data are not directly comparable"
    details: >
      LN2 (77K, 808 kg/m³) and LH2 (20K, 70.8 kg/m³) have very different
      fluid properties that shift all performance curves. Compression ratios,
      volumetric efficiencies, heat transfer rates, and valve dynamics all
      change significantly between fluids. The SPEED_SCALE_FACTOR in config.py
      was calibrated for LN2 and needs adjustment for LH2.
    impact:
      - "Flow rate scales with density ratio"
      - "Pressure build rate changes with bulk modulus"
      - "Thermal effects are very different (77K vs 20K)"

  pressure_drift:
    description: "Discharge pressure drifts down during extended fills"
    details: >
      Documented in Technical PDF p.22. The pump operates at approximately
      fixed pressure ratio. As the small test cryotank depletes, inlet
      pressure (PT110) drops, and PT130 follows. This is NOT a fault —
      it's an expected consequence of the small tank size.
    impact:
      - "PT130 and flow rate decline over extended fills"
      - "Production tanks will be sized to maintain pressure"

  subcooling_sensitivity:
    description: "Pump performance is very sensitive to inlet subcooling"
    details: >
      From Technical PDF p.17: the pump is 169x more efficient with
      subcooled liquid than with gas. Even small amounts of flash gas
      at the inlet significantly reduce volumetric efficiency. Ensure
      adequate subcooling margin (>5K) before starting fills.
    impact:
      - "Inlet quality > 0 = reduced efficiency"
      - "Subcooling margin < 2K = risk zone"

system_personality:
  recurring_issues:
    - priority: 1
      description: "ICV sealing is the #1 recurring issue"
      details: "3 occurrences in July 2025. Check ICV first for any pressure build problem."
      refs: ["2025-07-01", "2025-07-14", "2025-07-22"]
    - priority: 2
      description: "DCV sealing is the #2 issue"
      details: "1 occurrence. DCV polishing was effective but residual leakage remained."
      refs: ["2025-07-01"]
    - priority: 3
      description: "Safety loop tuning needs attention at high pressures"
      details: "AOV141 hunting observed. PID tuning required."
      refs: ["2025-07-22"]

  strengths:
    - "HP seal life is excellent (8.2M cycle lower bound = 3+ months at 20 fills/day)"
    - "Phase 1B achieved 100% uptime across 6 fills"
    - "Specific energy of 0.26 kWh/kg matches target"
    - "Back-to-back fill capability demonstrated (4 consecutive fills)"

  known_limitations:
    - "Pump gas ratio 14.4% vs 2.7% target — efficiency gap exists"
    - "Peak pressure 370 bar vs 700 bar H70 target — further testing needed"
    - "Small test tank causes pressure drift during extended fills"
    - "FT140 requires density correction for LH2 — raw readings are wrong"