Relative Humidity from Wet/Dry Bulb mechanism

Model scope

The named Sprung method is standard when the explicit equation, pressure units, ventilation convention, saturation phase, valid input range, and interpolation policy are fixed. Verdict is NEEDS_REVIEW because those implementation-defining choices are not fully specified, especially liquid-versus-ice saturation below 0 C and the exact psychrometric coefficient.

• The Sprung equation is not written explicitly in the specification. The standard water-surface form assumed here is e = e_s(Tw) - 0.00066(1 + 0.00115Tw)p(Td - Tw), with Tw and Td in degrees Celsius and p in hPa.
• Dew-point calculation is not defined beyond saying lookup table; the implementation must specify interpolation method and whether saturation vapor pressure is over liquid water or ice.
• The stated standard-ventilation assumption is incomplete: the psychrometric coefficient depends on ventilation/aspiration conditions, and naturally ventilated, aspirated, and ventilated psychrometers can require different coefficients.
• The specification does not state the valid constraint Tw <= Td. Readings violating this constraint can produce supersaturation or invalid results.
• The specification does not state whether relative humidity is clipped to the physical range 0% to 100% or whether supersaturation is reported.

Units and conventions

• Temperatures are in degrees Celsius.
• Station pressure is required in hPa for the Sprung coefficient; if supplied in kPa, convert using 1 kPa = 10 hPa.
• Saturation vapor pressures in the reference fragments are hPa and use widely tabulated WMO/standard meteorological values over liquid water.
• The psychrometric coefficient is A = 0.00066(1 + 0.00115Tw), appropriate to the stated standard-ventilation assumption.
• Dew point is obtained by linear interpolation in saturation-vapor-pressure-versus-temperature table entries.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "dry_bulb_C": 20,
    "wet_bulb_C": 20,
    "station_pressure_kPa": 101.325
  },
  "expected_outputs": {
    "relative_humidity_percent": 100,
    "dew_point_C": 20,
    "vapor_pressure_hPa": 23.38
  },
  "reference_data": {
    "saturation_vapor_pressure_hPa": {
      "20_C": 23.38
    },
    "source_convention": "Widely tabulated standard meteorological value; WMO/standard water-surface saturation table",
    "pressure_conversion": {
      "101.325_kPa": 1013.25,
      "source_convention": "SI exact unit conversion"
    }
  },
  "working": "Convert pressure: p = 101.325 kPa x 10 = 1013.25 hPa. Temperature depression: Td - Tw = 20 - 20 = 0 C. A = 0.00066(1 + 0.00115 x 20) = 0.00067518. e = 23.38 - 0.00067518 x 1013.25 x 0 = 23.38 hPa. RH = 100 x e/e_s(20) = 100 x 23.38/23.38 = 100.00%. Since e equals e_s(20), dew point = 20.00 C."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The Sprung calculation accepts physically impossible wet/dry readings that produce negative vapor pressure and a negative logarithm argument; dew point is undefined and the instrument should reject the input. The phase-table boundary and sign/unit conventions also materially affect results.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche7/tranche7-results.json
• BOUNDARY_HAZARD_CATALOG.json