Measuring Relative Humidity in a Stagnant Environment

Commercially available relative humidity sensors were evaluated when: 1) placed in chemically controlled relative humidity environments, 2) buried in stored corn with moisture contents in the range 10% to 26% db (40% to 95% equilibrium relative humidity), and 3) placed in changing relative humidities controlled with an environmental control chamber. Responsive elements in these sensors were made of a hygroscopic material sensitive to water vapor in stagnant environments. Observations were made over about a two-year period. The sensors were successfully used to determine moisture content of stored corn by measuring equilibrium relative humidity. Relative humidity indications were linearly related to corn moisture content. Sensors as calibrated at the factory gave very good indications of relative humidities over saturated solutions of LiC1 and K2SO4. However, sensors calibrated to operate in high relative humidity environments indicated a lower than theoretical relative humidity when exposed to the K2SO4 environment for only a short time. Many of the sensors, when moved from a low to a high relative humidity, approached equilibrium with the high relative humidity environment in a stair-step fashion. Equilibrium when sensors were moved from a high to a low relative humidity environment was approached more smoothly.