Calibration Protocols for Silicon Pressure Transducers under Humidity Excursions
Silicon pressure transducer calibration under humidity excursions requires multi-plateau RH dwells to decouple water absorption strain from pressure signals.
Relative Humidity Plateau
Equilibrium State
Stabilized level of water vapor concentration in a closed chamber is established when the rate of evaporation from a salt solution balances the rate of condensation. This stable condition, or relative humidity plateau, is used for calibration and verification of hygrometer sensors. The stability of this reference level relies on maintaining strict isothermal conditions within the calibration volume to prevent thermal gradients from distorting the local vapor pressure.
Generation Method
Saturated salt solutions generate precise and reproducible reference environments through the thermodynamic properties of dissolved salts. When a salt solution is sealed in a chamber, a relative humidity plateau is reached through spontaneous water exchange with the headspace air. Selecting different salts, such as sodium chloride or lithium chloride, allows calibration technicians to establish distinct humidity levels across the operational spectrum.
Drift Source
Thermal fluctuations within the test enclosure represent the largest source of uncertainty when establishing a stable reference state. A temperature change of only one degree Celsius can cause a substantial shift in the relative humidity plateau by altering the saturation vapor pressure of the water. High-accuracy calibration systems therefore employ active thermal shielding to maintain chamber stability.
Verification Protocol
Calibration procedures require that the sensor under test remain at the target level until its output signal stabilizes completely. This holding time is necessary to ensure that the moisture content of the sensor has equilibrated with the relative humidity plateau generated by the reference source. Automated logging software monitors the rate of change of the sensor output to confirm that thermal and moisture equilibrium has been achieved.