REFERENCING DILUTION-BASED TRACE HUMIDITY GENERATORS TO PRIMARY HUMIDITY STANDARDS

摘要

We describe a technique for measuring the trace humidity level delivered by a permeation-tube type moisture generator (PTMG). Mole fractions of H_(2)O in N_(2) carrier gas in the range 10 nmol/mol to 100 nmol/mol were considered. The measurements are referenced to the NIST low frost-point generator (LFPG). A quartz crystal microbalance (QCM) hygrometer is used as a comparator to measure the concentration difference between the respective outputs of the PTMG and LFPG. Differences in the water vapor mole fraction of 1 nmol/mol were observable with this technique. Systematic differences with respect to the LFPG output of (3.8±0.9)% and (2.9±0.7) %, were measured for two PTMG devices.