01
Best input pair and purpose
Use dry bulb plus measured wet bulb when working from a properly ventilated psychrometer; use dry bulb plus RH when you want the model wet bulb corresponding to an electronic probe. Wet bulb supports evaporative-process interpretation and is pressure sensitive.
The displayed value is thermodynamic wet bulb from the published psychrometric energy relation. It is not an automatic correction for a particular sling, aspirated or sensor-based instrument.
02
Verified worked example
At 25 °C, 50% RH and 101.325 kPa, thermodynamic wet bulb is 17.889 °C. At the same dry bulb and RH but 84.6 kPa, it is 17.460 °C. Pressure changes the mass relationship and the ideal evaporation balance even though dew point remains 13.864 °C.
The 7.111 °C sea-level dry-bulb/wet-bulb depression indicates capacity for ideal evaporative cooling, but it is not the temperature a real cooler is guaranteed to deliver.
03
Interpret the measurement carefully
A valid field wet-bulb reading depends on sufficient airflow, a clean fully wetted wick, suitable water, radiation shielding and enough stabilization time. Compare the instrument method with its manufacturer procedure before blaming the equation.
For process analysis, pair wet bulb with dry bulb and pressure, then inspect humidity ratio and enthalpy. The full state is more useful than a depression alone.
04
Frequent errors
Do not enter wet bulb above dry bulb for an unsaturated ordinary state. Do not reuse a sea-level psychrometric chart at elevation. Do not treat a non-aspirated surface sensor covered with water as a thermodynamic wet-bulb measurement.
Near freezing, water and ice conventions matter. Fog, droplets, solar loading and transient evaporation are outside the homogeneous equilibrium state.
05
Model limits and next action
The engine applies separate above- and below-freezing wet-bulb relations and reports solve failures rather than forcing a boundary. Review retained fixtures and tolerances on the methods page.
For an altitude job, compare the same dry bulb/RH at measured site pressure and standard pressure, then use the altitude reference to decide which downstream properties require correction.